Hi
this is only my 2nd post and have tried to find help using search but either not looking in right place or its not there.

My problem is that I can't stop warm air coming out of the heater. The system isnt out of control and does respond to changes of dial setting but on the coldest setting there is distinctly warm air still coming out of the vents.

Already tested:
- air con regassed and checked for leaks twice
- I have checked voltages to the duo valve which when dials are set to cold are 13.5v on all 3 terminals, when dials on hot are 13.5 on middle one and 0 on outer ones ( I think this is correct )
- cabin temp sensor and aspirator fan (both replaced)
- duo valve replaced then swopped back to old one as no improvement ( painfull ££)
- dust filter changed
- vacuum elements checked for leaks

any ideas appreciated also are there any more practical diagnostic tests I can do to track down the problem?

I still suspect the duo valve - are there any definitive tests I can do to make sure its closing fully?

thanks Keith

Hi Keith,

I've got a similar problem on a 230TE without aircon.

A 12v feed goes from the fusebox to the terminal 2 of the duovalve, and the feed continues from there, if I remember rightly, to the auxiliary circulation pump. When the control unit is calling for heat, terminals 1 and 3 on the duovalve will be at 0v.

If you unplug the duovalve, do you get full heat out of the vents? You may be able to feel the temperature of the outlet hoses to determine if the duovalve is closing fully. Have you tried tapping the solenoids?

Also does your auxiliary pump work (not that that necessarily has any bearing on the problem)? Under most conditions, you should have system voltage across the pump. If not, you might have a control unit fault, assuming that 12v is arriving on the electrical supply side of the pump, and that the wiring to the control unit is intact.

Sorry not to be more scientific. I may well be looking for a duovalve and an aux pump....

Krolroger (UK)

I do have system voltage on the pump, I have tried disconnecting it and it seems to have no bearing on the problem.

On the duo valve 1 and 3 are at zero when calling for heat and all three at 13.5v when calling for cold which I think is correct. I cant tell for sure the temp of the individual hoses as they are too far down for my large hands to reach but there is definitely warmed air coming through into the cabin., moreso I would say on the drivers side.

I did have a new duo valve fitted but had the problem with that one also so have taken it out again.

Would it hurt if I clamped off the feed to the duo valve to manually block the flow? or could this damage something?

Keith

I just came across your thread and realized that while we have different cars, we might have similar climate control systems. We for sure have the same problem.. Maybe the Euro thing makes for similar systems. What year is your machine ? I am enclosing the thread I wrote. See if it is in any way familiar. Only thing, My duo valve is a four prong connector - two to each valve. You seem to have a three prong ?

126 Duo Valve - what's with the heat...