Confused air conditioning

[jonnyc]

Occasionally when using the air-conditioning, the left hand vents dispense very hot air even when the rotary switch is set to the coldest position.

I have to stop the engine or set the rotary switch to the hottest position then return it back to the coldest position.

Is there an easy fix?

Thanks

Jonny

 

[jimmy]

Sounds like the duo-valve is sticking. It is located on drivers side, just in front of bulkhead, looks like 2 solenoids with heater pipes coming from them. Never experienced a problem myself but have heard that they are a common failure.

 

[Benzowner]

Had that probloem on my old W124 260E, was told by the dealer it was an expensive repair. Couldn't verify, never had it done, not much help

Edit, read the original post , mine was only a rotary heater control not air con

 

[janner]

Duo valves are about £160 but easy enough to change.
It could also be a faulty rotary switch but duo valve is more likely.
Edit: idea....
If you swap the two outside wires on the duovalve plug and the fault stays on the same side then it's the duovalve, if it changes to the other side then it's the rotary switch (or ECU).

 

[jimmy]

I have started intermittently having the same problem on mine just the last few days, the drivers side starts blasting out maximum heat, not much fun in this weather!! The only way to temporarily fix it is to stop the engine then restart.

Has anybody ever repaired the duo-valve or is it a replacement only job? Can anything be cleaned or lubricated?

 

[Shude]

moving to engine section

 

[Thmsshaun]

I had it with mine just a case of turning it up to hot and then quickly back down to cool.

 

[jimmy]

I had it with mine just a case of turning it up to hot and then quickly back down to cool.

Tried that, no good. Have to switch the fan off until I can pull over and stop the engine.

 

[DrNick]

Exactly the same as mine. Did the trick with swapping the wires and the fault stayed with the passenger side, so the duovalve was duff.
Got one from eurocar parts for about £110 +VAT. Fitting was relatively easy once you know how the underneath clips fit, which is apparent when you get the new one out of the box. Be careful as it is possible to 'ping' the clips off especially when putting them back, and they can go into very awkward places. I actaully tied mine on while fitting as I nearly lost one down the back of the brake servo. Once you have figured the clips out, it is literally a push on fit. The hoses to the top of it have to be removed obviously, but you can do it without draining the system as long as you don't mind a bit of water in the engine bay. Take care to protect the air filter/box from water as you don't want water in there. With care it will probably take about 30 mins to do. When complete, run the car with the heating on full and squeeze the top hose for a few minutes to remove any air that might have got in.

This is how I did it. Others may have a more professional approach to the job!

 

[chilled]

hi jonnyc

had the same problem on my 124 300e
i removed the duo valve and carefully removed the six screws holding it together, the valves in side were full of gunk
i cleaned all the parts and put it back together
its been working ever since
check the solenoids with a meter if the coils are OK give it a go
be careful not to damage the o rings and the rubber seal there are also two springs inside so be careful not to lose them

best of luck
chilled

 

[Dieselman]

hi jonnyc

had the same problem on my 124 300e
i removed the duo valve and carefully removed the six screws holding it together, the valves in side were full of gunk
i cleaned all the parts and put it back together
its been working ever since
check the solenoids with a meter if the coils are OK give it a go
be careful not to damage the o rings and the rubber seal there are also two springs inside so be careful not to lose them

best of luck
chilled

This is exactly the route I would take. I'm giving you a Rep point for this tip. :bannana:

I can't stand replacing parts without good reason. I'm sure the even the seals will be available, if not from an MB dealer then from a seal supplier.

It's worth noting that if the antifreeze hasn't been changed regularly then these valves will be more prone to gumming up.

 

[chilled]

hi diesel-man

not sure what a rep point is but thanks anyway

i only hope i can help someone again in the near future
its good to share

chilled

 

[Dieselman]

hi diesel-man

not sure what a rep point is but thanks anyway

i only hope i can help someone again in the near future
its good to share

chilled

The rep point is the little green square in the box below your avatar.

You deserve the point as you have probably saved a number of owners shelling out for unneccessary duo valves at £110 a pop.

 

[janner]

I would have thought the only way 'gunk' gets into the solenoid is coolant passing the gasket and rusting it.
Cleaning it out is probably not a very long term fix (but worth a try I guess).
Most duovalves fail because the rubber inside perishes allowing water into the solenoids or flowing constantly into the cabin heater.
MB do not make a repair kit for the duovalve but they do for the monovalve (as fitted to US models and those with auto aircon).

 

[chilled]

hi janner

the gunk in my valve was due to a head gasket going and the coolant being full of oil
the person driving it at the time didn't notice the car over heating and cooked it

chilled