Heater Blowing Cold

Hi

First post so if I'm in the wrong please please tell me and I'll move out and on kinda thing.

Now I have a 308D (1990) motorhome

The heater blows cold regardless of the settings or length of time on the road.

There appears to be some kind of valve under the dash near the accel pedal and the pipes there are warm

Been told it might be a blocked heater matrix but these are hard to change in terms of cost and time.

Questions

What else can I test?

What else could it be?

Can the heater matrix be back flushed? and can it be done insitu

Many thanks for any help to keep this old bird on the road.

Ian

Hi

I see no one has any comments or help for me

Is there another place in this site or another forum/site where I might find someone who knows anything to help?

Thanks

How's your coolant level? Low coolant = no heat.

Yes, it's going to take some disassembly and time.
You could try tracing the hoses back into the engine compartment and disconnect them there.
Then simply try running a garden hose into one end of the system, and see if it comes out the other end.

I have no idea if your vehicle has an electronic or simply mechanical valve regulating flow through the core.
If you've found where the "feels warm" *stops*, that valve could be removed (or the end closer to the "matrix" disconnected) and see if the garden hose flows through the matrix.
If it does flow, then it's the valve (or the signal that is trying to open it).
Measure signal to valve with voltmeter.
Remove valve, replace with short length of pipe, see if heat works (pointing finger of blame at valve or driving circuitry).

It's going to be tedious, and painful to reach, but that's how it goes. If you could get a replacement valve from a junk yard, you could simply swap it (but i'd still test with a voltmeter first).

If the valve is electronic, it may not be a simple "+12v" system... it could use a lower voltage, so simply hitting with the battery (without finding out the proper operating voltage) could damage it. Proceed with care.

good luck
--dick

First off, is it a Sprinter 308D or a pre-sprinter 308D? 1990 would make it pre-sprinter (1996 on) and my experience with my 312D sprinter may be of little or no use!

If it is a sprinter, the heater hose layout should be similar to mine. To try flushing in situ look for the 2 vertical rubber hoses on the drivers side of the engine bay leading down behind the cabin filter and windscreen washer bracket, one probably connects to a pipe or outlet on the drivers side of the engine, the other probably crosses the engine and then connects to the passenger side. find somewhere handy to disconnect these and flush with a hose (there may be a non-return valve in the hose on the pass side). Re-reading what you say about a valve and hoses near he accelerator pedal is making me think this is not a sprinter.

To change the matrix in a sprinter you will need to take the dash off and get to it from the top - actually apart from finding all the screws and manoeuvering the larger bits of plastic out of the vehicle, I didn't find it too difficult, but quite time consuming.

Hiya

Thanks for all your replies

I removed and replaced all the wires from the valve and reconnected and played with (pumped a few times) all the hot tubes and we now have heat

Outstanding issues:

1. The blower only works on high. The rocker switch seems to have way to many wires for me to work out what is what and therefore do any diagnostics to eliminate a fault switch. Anyone any ideas what all the connections on the switch are and how I can test it?

2. Boater... I think you're right this is not a sprinter... It is a 1990. I didnt know that. Is there a more suitable forum for pre sprinter vans. What were they called .... I guess not "pre sprinter". Its a 308D for sure.

Thanks for all your help so far and looking forward to any further help you guys can give

Just to confuse things with the T1N sprinters and the better known VW line of vans, the predecessor was known as the TN or T1, which stood for Transporter New (neu) or Transporter 1.
The wiki entry is here

You might find some specific help on the Benzworld forum, but the commercial vehicle sections are much slower for replies than this forum.

On the other hand some issues are fairly generic. Pretty much every heater blower has a resistor pack which does the speed selection - the switch routes power to various points along the resistor pack thus altering the resistance in the circuit and the voltage delivered - the fan speed depends on the voltage. The resistor pack will be mounted in the ductwork, probably near the main blower fan in the engine compartment (look for something with 4 or more wires (mine has 6 or 7) plugged into it that is itself screwed into the duct. The resistor pack is in the duct in the cold air flow to keep it cool - resistors generate heat. It has a thermal fuse on the end of it to protect it from overheating, however on max speed the switch effectively bypasses the resistors and thus the thermal fuse. Any time you lose all but top speed on the fan, the thermal fuse in the resistor pack has blown.

Mercedes (and every other manufacturer) want you to pay upwards of £30 (maybe upwards of £50 for a older vehicle) for an entire new resistor pack. Anyone with a basic understanding of electrics will work out the fuse rating (if you can see the writing or coloured band on it) and check a few website - maplin, farnell, RS - and realise that the fuse costs about £1.
It's not all plain sailing, to solder a new fuse on takes good skills with low power soldering, but if you are cunning about how you snip the legs of the blown fuse you can always crimp the new one to the legs of the old one with butt connectors, or use some small screw terminals.

Google "heater blower resistor repair" or similar and you should find some good descriptions and photos of what needs to be done.

Sorry I can't be more specific without knowing about the layout of the T1, but it looks like you have an OM601 engine like the early 308D Sprinters - if it wasn't for the shape of the bonnet being quite different it would be a fair guess that the layout would be similar to the sprinter, so just in case, on the sprinter the intake for the blower (the thing with the crossed out hose sticker on suggesting not to get water in it) is on the passenger side and the duct runs over the engine and up through slots in the top of the bulkhead to the heater matrix, the resistor is in the top of the duct between the intake/motor and the bit that opens up to get to the cabin air filter, so in the big scheme of things about 1/4 in from the passenger side of the van tucked up underneath the panel above the bonnet.

Of course you want to try and identify why the fuse blew, top contenders are water in duct shorting the resistor, and worn blower motor bearings and/or brushes making the motor draw excessive load. I changed the brushes on mine and lubed he bearings but it still isn't perfect - I might yet need to replace the motor if it ends up blowing the fuse again.

Jim