Yet more air con problems

[Wafter]

My 1995 E280 climate control throws out cold air. That is good. But it also constantly pours out hot air from the vents at each end of the dash. Sometimes it does this, sometimes, on good days, it works OK and cold air comes out.

Under the bonnet at the rear on the drivers side there is something that looks like an electronic valve. One water pipe from engine in, two that go behind dashboard out. When I squeeze one of the outlet pipes, the hot air from the dash vent gradually cools, so it looks like this is the problem.

Is my diagnosis correct? Has anyone got any experience of this? It's a Bosch unit so I suppose it is very expensive to replace. Can it be stripped and cleaned?

Any help would be appreciated

Alan

 

[guydewdney]

sounds like the duo valve...

probably 001 830 77 84 - 164 dollars US...

 

[Keith]

be careful you could blow ££s

Hi
I had an 18 month battle with my a/c on a 95 E300D. Its now fully resolved. I experienced similar symptoms and was badly advised to change several expensive componenets eg the duo valve and controller spending in total £750 on parts and labour before eventually discovering myself what the prob was and it took 30 mins to fix with a part costing £40.

A few q's
When it blows hot what happens if you slam the temp dials fully onto max cold , does it stay hot?

Is there a pattern as to when the prob occurs, eg first thing in morning but not evening or is it random?

If it misbehaves does it do it for the whole trip or can it settle down again?

there are a number of components that could be the cause my approach is to try the cheap options first then work to the expensive, unfortunately all the so called experts who helped me took the opposite route.

- air temp sensors (there are 3 that I found they cost about £10 each)
- air temp sensor fan (it costs around £40 and was my problem)
- duo valve (the bit you have identified - costs around £250 to replace)
- a/c control unit (in the dash console - costs around £400 to replace)

dont know where you live but I have a perfectly good duo valve if it happens to be the exact part no u need. I would be happy with £50 for it.

As a first step I would try removing the cabin temp sensor (located in the housing above the mirror). Let it dangle on its wire into the cabin and drive around like that for a while see if it cures the prob. If it does (as it did for me) it means the fan that sucks the air across the sensor has packed up and you are in luck for a cheap repair.

good luck :wink:
Keith

 

[Wafter]

Well thanks for the information. Up to tonight I would have believed that changing the duo valve would have fixed the problem though hammered my bank balance. Now I'm not so sure. I went out tonight and drove about 15 miles to Manchester. The first thing I noticed was that there was no air at all coming out of the central vent even though the blower was blowing away. I tried all combinations of switches but nothing changed. Hot air was still pouring out of the vents at the end of the dash.

With about 2 miles to go the situation suddenly changed and icy air started to come out of the centarl vent once more. I parked up and three hours later I started on my homeward journey and it was just as before, no air at all from the central vent, though a very small amount of hot air was bleeding through, and hot air pouring from the end vents.

I'm now begining to think it could be an electrical fault though I'm totally confused. Something is stopping the air coming from the central vent. I'm going to try Keith's suggestions and look at the temperature sensors first of all.

Thanks to eveyone.

 

[Keith]

a few more thoughts

I stick with the advice I gave in the previous mail in fact if you are getting inappropriate hot and inappropriate cold at different times it would suggest either (hopefully) a sensor problem or (if unlucky) a heating controller problem. Either way I wouldnt go for the duo valve just yet since it simply switches hot on and off and has no role to play in chilling the air. If the chilling is up the spout also it points to a more general control problem IMHO.

One way to emlinate the duo from your enquiries.....when its behaving properly if you slam the dials to max heat does it respond? Try doing it one side first then the other. If it does respond then its not the duo.

Try the trick of dangling the cabin sensor from the cabin roof for a couple of trips and let us know if this helps.

Keith

 

[Wafter]

Thanks Keith. I think you are right and that it is some kind of control problem. The air is definately being chilled, it's just not getting into the car. I'll try the sensor dangle today. By the way, the car has climate control rather than air con so I can't try both sides
Regards
Alan

 

[Wafter]

UPDATE
When I tried the car this morning the cental vent was behaving perfectly, lots of chilled air. The end vents were still pouring out hot air.
I couldn't do the dangle test as I couldn't get the roof light unit out. It was beginning to distort and I was afraid of it cracking.
I went to B&Q and bought a G clamp and clamped up the inlet pipe to the duo valve to stop any hot water reaching the heater matrix. The air con then worked perfectly. There was lots of chilled air everywhere and when I raised the temperature with the wheel the fan slowed down and eventually stabilised. When I demanded a lower temperature the fan speeded up.
Am I now correct in thinking that it must be the duo valve or is there still some other explanation? How can I check that there is or simulate, a signal to the duo valve to see if the solenoid works? What do you think Keith?
Regards
Alan[/quote]