How the water system works - pumps and microswitches.

I have seen a lot of questions recently about the water system in Classic Hymers.

Here is a rough description of how it all works - remember we are usually talking pre 95 vans, and different vans have different layouts. Also remember that in any old van, previous owners may have made modifications.

There are 4 main components to the basic water system - the fresh tank, the pump, the pipes and the taps. 

The original system is what is called a switched pump system. This differs from a house system in that it is not pressurised. In a house, the mains water is under pressure, so all you have to do is open a valve (a tap) and out comes the water.

In a switched system in a Hymer, there is a 12v pump submerged in the water tank. The pump is attached to a pipe that leads to all the taps. Each of the taps has a switch in it, and these switches are connected to the 12v battery system in the van. Every time you open a tap, not only does a valve open, allowing the water through, but the switch closes and supplies 12v to the pump so that the water flows. When you close the tap, the pump stops.

The reason they do this in motorhomes is that it is less risky to the van if there is ever a leak. If a pipe bursts, or leaks, or there is a loose connection in any of the pipes, the leak is limited to the amount of water in the pipes, and the whole tank will not empty into the van. This helps to prevent catastrophic leaks that can lead to expensive rotten damp damage. Of course it is not totally foolproof - if there is a slight leak that only drips a few drops every time a tap is operated, this can also lead to damp and rot damage. So in an old van, ot pays to regularly inspect your water system.

The switches inside the taps are usually called microswitches. If you look at the underside of a tap, you will see the water pipes going to it, and also 2 wires. In  some taps, these microswitches can be replaced - see picture below for a typical example.

If you do not hear the pump operate when you open a tap, and no water flows, then that is usually a sign that the microswitch isn't functioning. This can either be the switch itself which needs replacing, or the wires to the switch have come loose or damaged.

Another reason is that the pump is broken, or the wiring to it is broken or corroded. See troubleshooting common faults below ...

An idiosyncrasy of the system is that any tap will operate the pump, so if you have a broken switch in one tap, you can still get water out of it by opening any other tap. For example, if your shower tap isn't working, just opening another tap slightly, just enough to make the pump run, will enable the water to flow from the shower.

The next component after the pump is the manifold. A single pipe runs from the pump in the tank to a distribution manifold. This looks like a tube that has several pipes coming from it - see picture. It enables a single pipe to be split into several more pipes. In a normal setup, there are 2 manifolds, cold and hot. The cold feed from the tank goes to the cold manifold, and from there there is a cold pipe to each tap - usually kitchen, bathroom and shower. In some vans the bathroom tap and shower is a combined unit. From the cold manifold there is also a feed to the Truma hot water boiler, and then the hot water from the boiler goes to the hot distribution manifold, and from there hot pipes go to the taps.

On some older vans there are no manifolds - there are just a succession of T joints, which achieves the same thing - distribution. So if you don't find a manifold in a pre 1990 (roughly) van, look for T connections.
 
There are usually also 2 drain valves, one in the cold side and one in the hot side - both usually adjacent, and connected to, their respective manifolds. The cold drain valve usually has a metal body and a red or yellow plastic handle. This is to drain down the entire system for winter storage. The hot drain valve is grey plastic and looks quite different - to open it you unscrew the top. This will drain down the hot side of the system and is useful when you just want to work on the boiler, for example.

To drain down a van for winter, drain the main tank, isolate the pump - usually by switching off all 12v to the van with the big red isolation switch - open all the taps, and open the main drain valve. All the water in the tank and system should then drain onto the floor and the pipes should all be empty, and not prone to frost damage. Some main water tanks have drain plugs, which makes draining quicker and easier.

Then leave all the taps open and the drain valve open for the winter. Don't forget to close it before you fill up in spring, and it is always a good idea to check every joint for leaks and drops at the beginning of a new season.


Post 95 vans often have 12v electrically operated valves with thermostatic control - they will automatically open in a frost. After 25 years these get unreliable and are often replaced with manual valves, or held closed with wire or cable ties. But pre 95 classics have manual valves.

Taps - Usually in Hymers and most motorhomes, the taps are mixer taps, rather than individual hot and cold. A mixer tap has both hot and cold pipes leading to it. There are many types of taps - too many to list individually. Some taps have red and blue plastic push fittings, others have normal spigots and jubilee clips.

Common faults

As already mentioned, the commonest fault is a faulty microswitch. You may be able to replace the switch. Sometimes owners take the opportunity to replace an old tap with a new modern one. The modern silver Reich single level mixer taps are a common choice.

There are too many different taps for specific instructions, but here are a few guide notes. Look for "tails" many taps have factory fitted pipe tails, and it is the tails that connect to your pipes. Other taps have push fittings - so if you see no jubilee clips or other fixings, and wonder how on earth the pipes are connected, then get a grip and pull. Google for "caravan taps" and you will see lots of pictures. Most taps are secured to the sink by a large plastic nut. You may think - how on earth do I get a spanner on that - usually, you don't have to - it will be only finger tight. It may be stiff with age, but do your best to exert maximum force with your fingers before giving up!

If your switches are OK, and the pump is not running, then the pump, or the wiring to it, is suspect. The thing to remember about the original submersible pump, is that they are not intended to last for the life of the van - in effect they are a consumable. They rarely last more than 10 years in regular use, and they often can, and do, fail, especially after a long period of storage. But they are cheap - every caravan shop sells them, and any 12v submersible pump will do, from a cheap single barrel Whale, up to a Reich double barrel costing over £60 ... Most owners carry a spare, but they are easily available in all countries.

But before you buy a new pump, here are some tips to revive an old pump. They work very simply - a small 12v motor turns an impeller. Similar to a fish tank pump. The impeller can get stuck. if you have easy access to your tank, and can get your hand inside, reach into the water, grab the pump (with power applied by an open tap) and give it a good shake and knock - this will often free the impeller. If this doesn't work you can take the pump out and try again in the dry =- you may find the input chamber is gunked up.

The next commonest fault is a leaking manifold. The original plastic Hymer manifolds are subject to a lot of vibration over 25 years of travelling, and eventually they are known to develop cracks. Many a rotten floor has been caused by a leaking manifold, so it pays to inspect your manifolds regularly. If you do find a leak, you have several options. You can buy a new manifold from Hymer or any spares supplier. The new manifolds are stronger, but they are not cheap. Many owners make their own manifolds. There are several ways to do this - all you need is a method to join 4 or 5 pipes together. Popular choices are compression "T" fittings, or copper fittings. See pictures. As long as it is strong and watertight, you can use whatever method suits you.

Manifolds can also suffer from calcium deposits that build up over many years which can result in reduced flow. This is dependent on the hardness of the water regularly used to fill the tank. if you live in a hard water area and regularly have to descale your kettle, and you regularly fill up the van with the same water, this can happen. manifolds can also get clogged up with other debris.

The way to check if a manifold is in good condition is to identify the main feed to it. Then clamp of the pipe and undo it from the manifold. Then, with the pump running, release the clamp and let the water flow into a bowl or old towel. if the flow is strong, but the flow coming from the taps was weak, then the manifold is suspect. But if the flow is weak, then the pump is suspect.

Also, usually close by the manifolds, or close to the Truma boiler, you will find a drain tap. This usually leads from one of the manifolds and is a tap valve mounted on the floor. It has a lever on it to open or close it. This is the drain valve, and is used to drain down the system for winter storage. Draining for winter storage minimises the potential for frost damage to the pipes.

The waste water system - also called grey water.

Water that goes down the plug holes flows through grey waste pipes. These are slightly bigger than the water feed pipes, and they are different in that they are rigid pipes, joined together with push fit elbow joints. They usually are arranged in 90 degree angles. Under each plug hole is usually a trap - same concept as a domestic U bend, but these are usually round traps with concentric circular chambers that fulfil the function as a U bend, only in a more compact format. these are usually made by Reich. These traps are susceptible to clogging with old age - they get full of grease and gunk and old hair. 

These traps are serviceable. They can be removed by pulling off the grey waste pipe and then undoing the central screw in the  plug hole. They have a circular cover on the underside that can unscrewed revealing the insides. WARNING! Removing and servicing a trap can be fraught with difficulties and gotchas. They can get very stiff with old age - removing them can break or crack the hole in the sink. Very often when you screw back the cover of the trap, and the trap itself, you don't get a good seal and you will get a leak. It can be an extremely frustrating job, so my advice to you is not to take it on unless there is no alternative.

If you have a blocked or slow trap, try everything first before removal. If you do remove, be ready to order a new trap - it might be the only solution, so remember this if you are on holiday. Try boiling water, chemicals or gentle plunging. Trap removal should be a last resort, and only then if you have the skills, time and spares to deal with the job going wrong.

From the trap, the plastic waste pipes lead to the waste tank. As already mentioned, these are straight lengths of plastic waste  pipes joined with 28mm compression elbows. These elbows are prone to splitting and leaking, and again, benefit from regular inspection. There are no junctions in the waste pipes - they lead individually from the sinks/showers directly to the waste tank, where they enter into the top of the tank through elbows and big rubber grommets. The place where they do this is usually accessible, usually underneath a wooden panel. Another common fault is that many years of vibration can work the joints loose, resulting in leaks. They can also split with vibration and old age. Split elbows can be repaired using modern sealers and plastic glues. If using sealer to repair, the mating surfaces must be super clean. 

But please don't panic thinking that the system is unreliable - leaks are quite rare. All you have to do is to use common sense. 

Maintenance

Just as you maintain the rest of your van, it pays to maintain and check your water system, because leaks can cause expensive rot repair bills. All you have to do is keep an eye on things. 

Taps - every few months, put your hand up under the tap where the pipes attach, and feel for water. Same for the traps and waste pipes - obviously you can't get at all of them, especially the shower trap, but know your van, and take a regular look.

Everybody cleans out their boot or storage area occasionally - when you do, check for wet patches. Also - know where your manifolds are, and check regularly for leaks.

Another tip is to wait until somebody is having a long shower and look under the van for any tell tale drips, especially in the area of the shower tray and the grey tank. Do this once or twice a year.

Pump. Carry a spare!

Winter storage - draining the system.

Pressure Systems

Some owners decide they want more pressure than a submersible pump can provide. So they convert their water system to a pressure system. This is similar to the system used in yachts and boats. In a pressure system the submersible pump is discarded, and replaced by a simple pick up in the tank. The pump is then mounted externally to the tank. Popular pressure pumps are made by Shurflo and Whale. A pressure pump switches on when the pressure drops - ie a tap is opened, and switches off when the pressure increases - ie a tap is closed. This means that the entire system is permanently pressurised, just like in a house.

Advantages. Higher pressure - much higher than a submersible pump. Better showers.

Disadvantages. More prone to leaks, and when leaks do occur, they can be serious. Because the original van pipe system was designed for a low pressure system, and in the case of an old van - is old ... then suddenly increasing the pressure can result in new leaks occurring. So in the days and weeks after upgrading to a pressure system, all joints, taps and manifolds must be inspected and tightened if necessary and checked for leaks. This is not to say that the pipe and tap system is not suitable for higher pressure - it is, but it needs to be checked in an old van.

The other problem is that if a leak does occur in a pressure system, the pressure will drop, and the pump will operate - usually in small pulses. If the van is unattended, then the entire tank can be emptied through the leak, which isn't good. For this reason, pressure systems should have an isolation switch which cuts power to the pump, and the pump should be switched off when the van in unattended.

However, the upside of this, is that of you do develop a small undetected leak, the pump will pulse occasionally as the pressure drops, giving you warning. The pump will occasionally pulse randomly, but if it pulses regularly, say every 15, 30 or 60 minutes or so, then that is a sure sign of a dripping tap, or a leak.

Another thing to consider with a pressure system is that you will use more water. This can be an issue with showering, as too big a flow rate may empty your 10L hot water tank before you have finished your shower ... so there is a balance to be made.

Finally a few random notes. If you get black stuff in your mixer taps - this is a harmless bacteria. You can treat it with Elsil. 

Owners often ask if they should drink the tap/tank water. Other than making sure that the water is fresh - ie not from last summer! Then my answer is yes. There is no reason for your water system to be any worse than the mains pipes that deliver to your house. You may detect a plastic tinge from the tank. But basically it's up to you. I use it for tea and coffee, but for drinking water we refill containers with tap water. However, if necessary, I have no problem drinking it, and have done so for 20 years in many countries. You can buy filter systems, but I have no experience of these.

Manifolds - top one (hot) is a Hymer original. Bottom one (cold) is a home made copper one. You can also see the hot system valve at the top of this manifold.

Another example of alternative, stronger manifolds - these made by Snailvans in Leicester I believe.

Drain valve - also available in red!

A new Reimo manifold - not cheap!

Typical Microswitch

Typical modern mixer tap - many other designs available

A typical external 12v pressure pump

A typical standard submersible pump

Typical tank layout
The pump is submerged under the orange hatch. Black hatch is for inspection/cleaning - it can be other colours.

A= Main feed pipe to water system (taps etc) with non return valve to stop system siphoning back

B= Tank venting to allow filling without blow back at filling point 

C= Non return valve allowing air back into the pump allowing it to drain and be frost protected when the tank has been drained. 

Typical concentric odour and waste trap - one end is usually blocked off, and in Hymers they are usually white. 

Waste pipe elbow - occasionally prone to splitting with old age.

Turning fridges upside down - The truth about the myth.

The following information is not my personal opinion, it comes from a well respected industry professional.

I have lost count of the number of times I have seen online people advising to remove a 3-way fridge that isn't working properly, and invert it or rotate it. 

The reason this myth perpetuates is that very occasionally it does work, but only occasionally, and to actually work, it must be done in a certain way, and only under certain conditions. If it is done the wrong way, it can actually finish off a fridge that otherwise might have been saved.

The first thing you have to check is this - if the fridge works OK on 220v or 12v (while driving), but not on gas, then rotating it or inverting it will not solve anything, and may finish it off completely. If the fridge works on any one of the 3 power sources then that means there is nothing wrong with the actual fridge cooling mechanism, and therefore it should not be inverted or rotated.

There are 2 reasons why a fridge may not be working on any power source. The first is that the chemicals inside the tubes may have separated, usually through old age and not being used very often. The fix for this is vibration, not inverting or rotating. The best way to vibrate a fridge is to find a cobbled road or rough track and take the fridge for a rough ride. This has been proven to work on many occasions. 

The second reason is that in an old fridge, the pipes and tubes that contain the chemicals may have corroded internally and bits of corrosion have blocked the evaporation venturi. This is a small hole in the piping system through which the chemicals are forced as part of the cooling process.

And this is what gives rise to the myth - if this hole is blocked by internal debris, and the fridge is rotated the right way, then there is a chance that the debris will be dislodged. But if rotated the wrong way then even more debris may be forced into the hole, making the blockage even worse and possibly damaging the fridge beyond repair.

The only time it is advisable to rotate the fridge is when you are sure that there is a working heat source, yet the tubes at the top of the fridge do not get warm, and you have tried upright vibration. Then it is essential that the fridge is rotated in the correct direction, so that the rotation pushes any debris AWAY from the hole, rather than into it. And even then, this method has only an approximate 1 in 4 chance of success. If rotated correctly, no further damage will be done. But if rotated the wrong way, then the problem could be made worse. After rotation, before re-installation, put the fridge on 220v on max, and see if you have been lucky. If not ... it's usually time for a new fridge.

So which way is the right way? As you look at the back of the fridge, with the chimney on the right, it is anti-clockwise. Rotate the fridge (2 person job) smoothly as you can 3 or 4 turns anti-clockwise.

It must be stressed that this is a last resort, and only has a low chance of success. But occasionally it does work, and this is what has given rise to the online meme that is increasingly being advised for just about any fridge problem.

I have also been told about another method to try and revive an old fridge. Run it on 220v AND gas at the same time, with the thermostat on full. This extra heating is often enough to remix the chemicals and get things working again. Whether you can do this easily depends on the model - some fridges have controls where you can run on both at the same time, others don't. If not, you have to manually hot wire the 220v element around the back so it runs while on gas.

The commonest problem with old 3-way fridges is "not working on gas". The usual reason for this is lack of maintenance and cleaning. The gas part of the fridge is far more prone to failure than the electric part. The electric part is just an element, similar to a kettle or immersion heater, and it either works or it doesn't. The same goes for the 12v element.

So the first thing to do with a fridge not working on gas, is to connect it to 220v and turn it up to max. The chimney and the pipes should get should get hot. If not - the 220v element is suspect, and should be checked.

Only if there is heat from the 220v element, but no cooling, should you then consider removing the fridge and vibrating or rotating it.

If the fridge works fine on 220v but not on gas, then there is no point in removing, vibrating or rotating, and the good news is that gas problems are usually easy to fix, either by the owner or a professional, and at reasonable cost. 

The commonest problem is dirt or dust obstructing the gas jet - there are plenty of articles and Youtubes online on how to clean the burner and jet.

Fridges don't last forever - but many last for 25 years or more, which is fantastic compared with normal household appliances. Just don't finish off an otherwise fixable fridge by believing everything you read online. Removal, inversion and rotation is a last resort, after everything else has been tried, in a logical manner.

The classic Hymer fuse panel - explained and maintained

There have been quite a few issues and questions with habitation electrics recently, so let's dive into that mysterious brown panel down by the drivers left knee .... (in a LHD van).

Unlike post 95 vans, which have more complicated electrics, usually based around an Electroblok, pre 95 classics have quite straightforward habitation electrics and distribution, and at the heart of this is the fuse panel, found at the front of the van, under the dash on the left, usually close to the drivers left knee. There is also usually a big red cut-off switch mounted next to it.

(NOTE ... this article is about the fuse panel found in pre 95 coachbuilt Hymers - B544 and S555, B694, S660, and others ... but the Hymer Camp 65, 55 and 52, with metal cab and bed over, are different - there is a section on this at the end, but the whole article is still relevant, only the locations are different.)

The panel has a hinged front which pulls down, to expose a bank of 8 fuses. The type of fuses used in classic Hymers are known as barrel fuses. They were originally designed and made by Bosch, the famous German electrical company, so they are also called "Bosch fuses". Many UK sellers - Ebay etc also call them "European" fuses. Barrel fuses are not so common nowadays, having been replaced in more modern vehicles by blade fuses, but that is not to say that they are old fashioned or ineffective in any way, but it is true to say that they can be a bit more prone to failure from old age than their more modern blade counterparts. They are also slightly more awkward to insert and remove than blades.

The best fuses to buy have ceramic bodies, so search for these. Cheap Chinese ones have plastic bodies - they do work OK, but there have been occasional reports of them melting, but this is most probably down to a massive fault elsewhere, not the fuse itself. Halfords sell the thermoplastic body ones, which are fine.

Edit 2023 There has been much discussion on fuses since I wrote this, so here is more info on fuses.

Just because one or two people in 20 years had plastic barrel fuses melt does not mean to say that all plastic fuses are dangerous. The reality is that the stories came about because the fuse was overloaded anyway. A fuse is designed to blow immediately in the case of a short circuit - that is its only purpose. If that fuse is getting hot and eventually melting, which takes time, then the fuse is the wrong rating because the circuit has been overloaded. A fuse, even a Chinese one, should pass the designed current and stay cool. The rue of thumb is double. So a 16amp fuse should handle an 8 amp circuit and stay cool. If you consistently pass 16a through a 16a fuse, it will fail eventually - a ceramic fuse body will withstand the heat, but the metal fuse wire will eventually fail. A plastic body fuse may melt before the wire fails, but it is still doing its job, and I have never heard of a fire being caused by a melting plastic fuse - even the Chinese know not to use superflammable plastic types. But all failures are not the fault of the fuse, they are the fault of the designer/installer.

But it is also fair to say that some stuff from China is pretty poor, but this is common knowledge, so just why buy fuses from there in the first place?

The reality is that you need a fuse asap, and the quickest place to get a fuse in the UK is Halfords. In fact Halfords is just about the only place you can get a barrel fuse over the counter. And Halfords are a big company and they don't sell crap - or rather they do, but at least it is tested to a minimum standard - they don't want returns or lawsuits. So if it has to be now - Halfords.

But if you can wait a few days, and are a perfectionist, then the ones with ceramic bodies are the best. But as mentioned above - they are only "best" at taking abuse. Before blade fuses were introduced, every fuse in every car was a barrel fuse, also called Bosch type, or Euro type. And I have seen Ebay sellers advertise ceramics. Just search.

I can't honestly tell you what fuses are in my panel - honestly! I am sure the bottom 3 must be original - they are very low current. The rest can carry between 8 and 16 amps, but rarely do so, especially these days as most owners have converted to LED lights. I remember making a mistake a few years back and accidentally shorting a wire during a job - the fuse blew immediately - it did its job. And I just went to my box and got a new one - I have no idea if they are ceramic or plastic, all I know is that they were not sourced from China. But if I did source from China, I would just make sure that the circuit was in good order. Any fuse that melts is not the fault of the fuse, it's the fault of the circuit. Original article continues ....

In the Hymer manual the 2 most common fuse sizes are 8a and 16a - red and yellow. For some reason modern red and yellow fuses are rated at 10a and 20a - this is absolutely fine - use 10a for 8a and 20a for 16a - no problem at all, you will still get the same protection and function.

The fuses are held in place by a spring clip at one end, and a recessed hole at the other. To remove a fuse, you just have to grab it tightly and pull it out. To insert a fuse, you locate one end into the recess hole on the right and then push the other end into the spring clip on the left, where it should locate nicely in the depression in the click. The pressure of the spring clip on the left then holds the fuse securely in place and forms a good electrical connection at each end. A useful tool for inserting and removing barrel fuses is a small pair of long nose pliers, although it is perfectly possible to do it by your fingers alone.

At each end of each fuse you can see that there is a screw terminal which attaches the wires to each end of the fuse holder. These wires are just visible down each side, and they disappear behind the panel. 

The fuse panel isn't actually just a panel - it's a box, and the box extends for about 30cm behind the panel. There are 4 screws that hold the panel/box in place, and if you remove these, you can then pull the panel forward, exposing the box behind.

This box contains several components that are critical to the correct operation of the habitation electrics. These are the relays, and the shunt, which will be explained later.

At this point it is important to understand the distinction between "habitation electrics" and "vehicle electrics". Habitation electrics are everything in the living area of the van - the lights, the Truma stuff and the water pump etc. Vehicle electrics are everything to do with the base chassis ie the Mercedes, Fiat or other chassis onto which Hymer built the rest of the van. The vehicle electrics are completely separate from the habitation electrics. The vehicle has its own separate wiring and it's own separate fuse box. There is no common wiring between the two, they are completely different systems. There is only one single electrical connection between the vehicle electrics and the habitation electrics, and that is a single wire that brings 12v power from the vehicle charging system, to the habitation system. 

Many owners get confused about this, so it is important to grasp. If you have an electrical fault with the vehicle, like a tail-light, or headlight, or wiper, or any one of a hundred vehicle related faults, then you have to be looking at the vehicle system, not the Hymer system. Similarly, if you have a problem with the Hymer habitation electrics, there is no point in looking at the vehicle fuse box or wiring for a fault. So know the difference between the two, and know where your base chassis fuse box is. In Mercedes chassis it is always in the passenger footwell. In Fiats and others it varies, but is also usually in the general area of the passenger seat also.

So back to the Hymer fuse box.

The biggest and most common problem is old age and corrosion. When your classic Hymer came out of the factory 30 years ago, all those bits of metal in the fuse panel were all shiny and brand new. But over all those years, as with any metal, the surfaces of metals gets corroded. The same goes for the fuses - the strip of metal in the fuse can also get corroded. Eventually the corrosion builds up at the ends, and starts to interfere with the electrical connection. Electricity can not pass through corrosion - it needs to pass through a connection that is bare metal to bare metal. Unfortunately this is a very gradual process - it just doesn't happen overnight (although it does sometimes!). As the corrosion builds up, the electricity finds it harder to flow. This is called resistance. As resistance builds up, more electricity is needed to overcome the resistance, and ultimately one of two things will happen. Either the connection will break down completely, and the electricity will cease to flow, or the fuse will blow.

The same thing can happen elsewhere in the van. If any of the connections in the van get corroded and start to draw too much power because of corrosive resistance, then eventually a fuse will blow. This is what fuses are for - they are doing their job.

So that is the theory - how does it work in practice? Well it is really quite easy. All you have to do is clean the fuse panel. This is a job that should be done in every classic Hymer every 5 years or so. All you have to do is to remove each fuse and inspect the ends. Corrosion can either be quite invisible, or obvious. All you need to do is to rub the end of each fuse with something abrasive. This can be a bit of sandpaper, or a nail file, or the file bit of a swiss army knife - it's just common sense. You may even decide to just replace the fuses with new ones - after all they have been there for many years, and they are very cheap.

Next, you need to clean the ends of the fuse holder. At the spring clip end, you can use a cotton bud dipped in solvent. Or you can carefully use any pointed instrument. You don't have to bring it back to a new polish, all you have to do is break the surface of corrosion. Just a few scrapes is all you need so that you can see a bit of shiny metal. At the other end, the bit with the hole, this is a bit more awkward, but usually there is less corrosion here, so quite often a wipe is all that is required. Just use common sense. The main requirement is to get metal on metal.

Don't worry about the electricity - unlike 220v in your house, which can kill you, 12v is harmless, so you can touch it with your bare hands. 

Once this is done, for all the 8 fuses, you are good to go for another few years.

If you are trying to fix a fault in an emergency, it is worth remembering that if you do have a corroded fuse connection that is causing part of the van to go dark, simply removing the fuse and replacing it is usually enough to cut through any corrosion and remake the circuit. If in doubt, and several lights or appliances are not working, remove and put back all the top 3 fuses. It could be a simple fix. It is a very common problem in old vans.

Another very common issue is that a fuse can look OK, but the ends are corroded so that no power is flowing - so don't be fooled by this. Remove each fuse and replace it, even if it looks OK.

Finally, if you are doing a full service, take a good look at where the wires are attached to the screw connections. If the wires are still looking shiny then all well and good, but if you see any green gunge, then that is corrosion. It isn't a serious problem, a bit of corrosion doesn't do any harm, but best to give it a spray of WD40 and clean it off with a stiff brush or whatever you have to hand. Then, with a screwdriver, give each of the screws a quarter turn anticlockwise, as if unscrewing it, then tighten it back up again. This will break through any corrosion deep inside the connection, and make the connection 100% again. Problems with these connections are rare, but while you are at it, it is such a simple thing to do, so daft not to.

So now you know how to refurbish your fuse panel, let's talk about what the fuses actually do. If your Hymer still has its documentation, then somewhere there will be a fuse diagram, but many classics are either missing their manuals, or the manuals are in German. However, in most classics with the standard fuse panel, the layout is always the same.

The top 3 fuses are the most important ones. All power to the habitation electrics go through the top 3 fuses (with a couple of exceptions depending on what model van). If you look closely, you can see that they are all connected together by a strip of copper on the right hand side. Which fuse is connected to what in the van, depends on your layout and van model, but if something has stopped working somewhere in the van - ie the lights, or a Truma, or the pump, then it will most likely be powered through one of the top 3 fuses. There are other single fuses and junction boxes in the back of the van, depending on your model, so the fault may be with one of those, but generally, all power goes to the van through these three.

It is worth remembering that if one of the top 3 fuses has a problem, then more than one thing in the van will not be working because each fuse feeds power to a group of things, not just one. If just one single thing is not working, but everything else is OK, then it is unlikely to be one of the top 3 fuses, and more likely to be a problem closer to the thing that is not working - a loose connection, or something - every van is different.

The next fuse down is number 4. This fuse is for the battery charger. When the van is hooked up, the charger operates and supplies 12v to the leisure battery. This power comes through fuse 4. It is the only function of fuse 4. 

Fuse 5 is the fridge 12v fuse. When the engine is running, 12v is fed to the fridge via fuse 5. This is the only function of fuse 5.

Fuses 6 7 and 8 are the fuses for the panel meters - the two meters that show battery voltage, and power - the famous Strom meter. These fuses only affect the operation of the panel meters, and do not supply any power to anything else in the van.

However there are many different van models, and there are some differences, but in general the top 3 fuses are the main fuses. Many vans have additional fuses - for example there is often a fuse in the bathroom. On some models, power for certain appliances is taken directly from the leisure battery, via a separate fuse. An example of this is the S700, where power for the front Truma heater is taken directly from the battery box. You need to be familiar with your van to know if you have any extra fuses hidden away anywhere.

Finally, let's explore the box behind the panel. This can get a bit technical, but it's worth knowing what goes on in there. The first thing to know is how to get the box out - it can be a struggle. After undoing the 4 front screws, the box should pull forward, but very often it only comes about half way, and then seems to get stuck. This is because there are a couple of bits of metal sticking out of the frame that hit the side of the panel hole. What you have to do is wiggle the box up and down as you pull forward, so that the bits of metal get over the edges of the hole. It's difficult to explain in words! But the whole box will come out, as shown in the picture. 

There are 3 components in the box - 2 relays and a shunt. the relays are small black (or occasionally silver) boxes - one bigger than the other. The shunt is a horseshoe shaped piece of copper located at the back of the box - see photo.

The bigger relay is relay 1. Relays are basically just remote controlled switches. This relay is connected to the vehicle electrics - ie the starter battery, on one side, and the leisure battery on the other. The relay only operates when the engine is running, so that power can flow from the vehicle alternator to the leisure battery. When the engine is off, then the relay is off, and the leisure battery is isolated from the vehicle battery. this means that you can run down your leisure battery, and the van will still start. Relay 1 is critical to the operation of the habitation electrics, but thankfully it is a very reliable component and rarely fails. But if you are getting no charge to the leisure battery while driving, and you have checked everything else, then relay 1 has to be checked.

Relay 1 is not Hymer specific - it is a very common automotive relay and available almost everywhere. The original relay is 70 amp - these might not be easily available over the counter at your local car parts shop - they are usually anything between 20 and 50 amp - but you can use a lower rating to get you going again - Hymer as usual used a high rating quality relay that would last for years, but in reality more than 20 amps flowing through the relay is quite rare. A 50 amp one will do permanently, and any lower figure can be used temporarily - especially in a standard van with just the usual single leisure battery.

To troubleshoot the main relay - the easiest check is to put your finger on it and feel for the click when you either switch on the ignition (Fiat) or start the engine (Merc). The relay can only be broken 2 ways - either permanently open or closed. If stuck open, then you will not get any charge through to the LB from the VB while driving - you can check this with a meter - the VB should be up over 13v but the LB will be unchanged at around 12v. With a working relay, both batt voltages should be the same with engine on. If the relay is broken closed (rare but can happen), then the LB and VB batts will be the same voltage with engine off, and both will run down together because they are now in parallel due to a permanently closed relay. 

The smaller relay is relay 2. This also only operates when the engine is running, and supplies 12v to the fridge while driving, via fuse 5. Troubleshoot this by feeling for the click. Be aware that it is very rare for the fridge relay to break - usual causes for no 12v to the fridge while driving are either the fuse, dirty fuse connections, corroded 12v connections at the back of the switch or a faulty red 12v switch on the fridge itself. All these have to be checked before you go to the hassle of pulling out the fuse box to get at the relay. If you have 12v at fuse 5 (in most vans) then the relay is working.

The shunt - this gets a bit technical, but the shunt is a device through which all 12v power in the habitation electrics flows. The shunt senses how much power is flowing, and in what direction, and then sends this information to the power Strom meter in the main panel, via fuse 6, so you can see how much power you are using, or receiving, on the meter. In the red you are using leisure battery power, in the green you are receiving it - either from the engine, or from the charger, (or from solar. However because solar systems are not factory fitted, not all solar panel installations register on the Strom meter, because whoever installed them didn't connect them through the shunt.)

There is very little that can wrong with the shunt - it is a thick copper wire. However, there have been instances where the shunt has completely corroded away and disintegrated, If this happens, all power to the van is lost, and it can be a real head scratcher, so it is worth mentioning. A corroded shunt is caused by road spray from the engine compartment getting into the back of the box. Normally there is some protection to prevent this, but if this protection has come loose, perhaps from accident damage or some other engine work, then a lot of water and damp can get into the back of the box and corrode away a shunt over 20 odd years. It is very rare, but has been known to happen.

Another reason the shunt can be damaged, even completely destroyed, is if somebody previously has connected the leisure battery the wrong way round. This can result in enormous current through the shunt which will melt it. This is rare, but I have seen it twice in 20 years.

The plastic cover to the fuse box - that hinges down, is actually the same component as the cover on the hookup cover on the side of the van. These are easily available on Ebay and from caravan/motorhome shops. See photo below.

The big red cut off switch. This does what it says on the tin. It is there mainly for safety - if you have a fire or a funny electrical smell then this is the first thing to do. It is also used for winter storage. There are two things to remember about this switch - it is a bit awkward to use, and can occasionally be operated inadvertently. Many a red face has been caused by this red switch. Secondly - it can very very rarely, fail completely. I have only heard about it once in 20 years. So if there is zero power to the van, and the shunt is OK, and all else has been checked, then the switch has to be checked as well. This can be done with a multimeter.

So that is just about everything I know about the classic Hymer fuse panel and box - if I have missed anything, please comment below.

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The shunt

A home made shunt repair using the original eyes and 2mm copper wire. To do this you will need a good soldering iron. And please note that the dimensions are critical - it is unlikely the new one will be exactly the same as the old one, so the meter may not indicate accurately (if the meter still works). You would have to calibrate with a multimeter.

Typical fuse layout

Typical circuit diagram

The relays - can also be black

Replacement cover - same as the EHU cover.

EXTRA NOTES FOR HYMER CAMP OWNERS 

This is a Hymer Camp - with metal cab.

The Hymer Camp does not have the fuse panel as described above - Camp electrics are under the front passenger or drivers seat. Under the seat you will find the leisure battery, the EHU charger, the fuses and the relays. Operation of these is exactly the same as described above. There are only 4 fuses in a Camp. 

There is no shunt in a Camp, and so no Strom (amps) meter.

Some Camps have a main on off switch on the panel - usually marked in German 12v ein aus - 12v on off. This has the same function as the big red switch in the other Hymers - it isolates the leisure battery - ie switches habitation power on and off. The actual relay is the big black box next to the charger. It s a latching relay made by Schaudt, and is remotely controlled by the panel switch. They are not known to be unreliable, but on the other hand some have been known to fail. If you have no hab power and you know the battery is good, then it is easy to test the relay - it has 2 thick wires in and out that carry the battery power between the LB+ and the distribution connector block, and 2 small wires that go to the switch. Short out the 2 thin wires and the relay should operate, if it does, then the panel switch is faulty. if it doesn't, then short out the 2 thick wires. if power comes back on then the relay is broken. In which case temporarily fix the problem by disconnecting the 2 thick wires and connecting them securely together and taping up. This will get the power back on, but you lose the ability to switch on and off from the panel.

Engine battery connection is a red cable that comes from the engine battery positive, via a fuse in the engine compartment, to the bigger relay, via the connection block.

Camp under seat electric box - battery removed in this photo

The charger is often coloured blue or silver.

Camp circuit diag - all pre 95 Camp models are the same

Camp fuses

Mercedes automatic gearbox only working in first and reverse gears

I am not very knowledgeable about auto gearboxes, but I came across this problem that turned out to have a nice easy answer.

This applies to all Mercedes auto gearboxes from the 80s and 90s, so all classic Hymers.

A guy posted on the "Classic Hymers Technical" Facebook group that his 1988 S550 auto would only work in first gear or reverse.

It turned out that it wasn't the gearbox at all! It was the kickdown switch located under the accelerator pedal. Some stuff had got in there and it was stuck on.

A nice easy fix, for what might have been a horrible situation.

There is a Youtube about it.

https://www.youtube.com/watch?v=zyMELI4yh-M

Solar Charge Controllers explained my way!

The Basics - what it does.

A solar charge controller - SCC for short - converts the power from a solar panel into power suitable to charge a battery - usually, but not always - 12v.

A solar panel converts light into power. As the light increases and decreases, the power also increases and decreases, as you would expect. As the light increases and decreases, the voltage from the panel does the same. But in order to charge a 12v battery efficiently, you need a constant voltage, and this is what the SCC does - it converts a varying voltage to a constant one.

So in a basic setup you connect a panel to the SCC and the SCC to the battery. 

What the numbers mean

Solar panels are specified in watts, but SCCs are usually specified in amps, which can be confusing if you don't understand the relationship between volts, amps and watts. There are technical reasons why this is so, but I want to try and keep this simple. In order to match an SCC to a panel, you take the amps of the SCC and multiply it by 12 - volts X amps = watts - So if you see a 12v  SCC advertised as 10 amps, then 10 x 12 = 120. So the max panel that SCC will cope with is 120 watts.

Or you can work it back the other way. If you already have a panel and you want to choose a 12v SCC, then you divide the watts of the panel by 12 and the resulting number is the amps the SCC has to deal with. So for example a 200w panel needs a (200 / 12) 16.6 amp SCC. As with most things electrical you add a bit on for safety, so in this case you would probably choose a 20 amp SCC.

If you have multiple panels, then you just add up the watts and perform the same calculation.

Most vans will usually have just 1 or 2 panels, but sometimes more on a big van. If you are looking at a multi panel setup, then you also have to decide whether to connect them in series - ie daisy chained, or in parallel, this decision has an effect on which SCC you choose. However, for now, I want to keep it simple, so we will just talk about a 1 panel setup.

The final part of the calculation is to do with your battery setup, and what you can expect from your solar system.

A 12v battery likes to be charged at roughly 10 to 20% of it's total capacity. I prefer to use the higher figure. So a common 100ah battery - that's 100amps for 1 hour, or 10 amps for 10 hours ... etc, will benefit from a charge of around 20amps, maximum. If that battery is flat in the morning, then in theory, on a sunny day, a 200w panel should charge it back up in about 4 or 5 hours.

A reasonable rule of thumb is that you should have roughly 1 or 2 watts of solar for every 1ah of battery.

PWM or MPPT - what it means

The next choice you have to make is what type of SCC you want. You will probably have seen that there are 2 types - MPPT and PWM. These refer to the design of the circuits inside the SCC.

PWM stands for pulse width modulation. How this works in very simple terms is that if you have a higher voltage and need to convert it to a lower voltage, you can do this by "pulsing" the higher voltage - if there are gaps between the pulses, then for all intents and purposes the pulsed higher voltage appears to be lower because it averages out. That is an extremely over simplified analogy, so tech folk please don't criticise! The pulsing is done by chips - integrated circuits - and these chips are really simple because they only have to count and time the pulses and gaps. So PWM controllers are the cheapest. And they work fine.

MPPT stands for maximum power point tracking. How this works is that electronics in the SCC "tracks" the variable voltage from the panel, and calculates the most efficient way to convert it to the required lower voltage to charge the battery. It does this in real time, so it basically needs more complicated chips - tiny computers, and the voltage conversion is done by powerful transistors. This means that they are more expensive than PWM, but they are also more efficient - about 25% better.

MPPT controllers used to be so much more expensive than PWM that they were out of range for most users, but as with most things, prices have come right down in the last 10 years.

PWM controllers still have their uses, but nowadays most van owners will go for MPPT.

However there is a problem with crime and counterfeiting. Many cheap Chinese SCCs on Ebay and Amazon are labelled as MPPT, but are really PWM inside. Unfortunately there is no way to check in advance, and the only way to check the difference between the two is with test equipment. So it's a bit of a lottery, and most folk just never know, and of course the police and the government don't care. However I am not saying that all "noname" SCCs on Ebay are fake - just that the likelihood of ending up with one is higher. The "nonames" are also usually over specified - like broadband speeds - so a cheap SCC advertised as 20amp, will likely be a lot less. 

Recommendations 

So the best advice is to buy a recognised brand and spend a bit more. It's not like the difference is hundreds - it's tens. In my experience the best budget range of genuine MPPT controllers are made by Epever and are called the Tracer range. They are very popular, and readily available. I have never seen or heard of a counterfeit Tracer. 

The next step up is Victron. Victron are the BMW or AUDI of the industry. Their controllers are about twice the price of anything else, but they are the best you can get, but are still affordable for reasonably small van installations. Additionally, Victron are at the cutting edge of design, and nowadays their stuff comes with Bluetooth functionality so you can always see what is going on on an app in your phone.

But for most folk, a Tracer will do the job nicely. It's what I have been using for years.

Another way to protect yourself from dodgy gear is to use a reputable UK company. There are several in the UK, but I can recommend 2 off the top of my head - Bimble Solar and Photonic Universe - both easily found online. Anything these guys sell will have been checked for quality and specification, and you can buy with confidence.

"Load Terminals" - what are they?

Finally - I just want to say a word about a situation that I have found many times causing confusion online. Most controllers - SCCs - come with 6 terminals. 2 for the solar panel in, 2 for the battery out, and 2 usually marked "load". It is these extra 2 load terminals that cause confusion. In a van installation, these terminals are not used, or if they are, their use needs to be understood.

The load terminals are for other applications. In a very simple installation - for example a solar powered outdoor light or whatever, then the light, which is the load, could be connected directly to the load terminals of the SCC, rather than all the way to the battery, which could save wiring. But in a van, where you are adding solar, the battery is already connected to all the stuff in the van, so there is simply no need to use the load terminals on the controller and they are left unused. The confusion arises because of the way it is labelled - people think that just because there are 2 terminals, they should be connected to something. But in the majority of van installations - they are not needed, and not used.

But you can use them if you want to in certain situations - if you do happen to have something new that needs 12v in the van, and it is closer to the SCC than the battery, so will save wiring, then you can connect it to the load terminals for convenience - it is just another connection to the battery. If you do this, and your SCC has a display, bear in mind that the display's "load" section will only display the values for whatever you have connected - not the whole van.

Above is a basic Epever Tracer 20 amp MPPT - less than £50 (2019)

An example of a Victron MPPT - generally recognised as the best available.

This is advertised on Ebay as MPPT - for less than £10 - I wouldn't, and neither should you!