Constant hot air from side vents, not Duo-valves (W124)

[MercStraight6]

When I bought my W124, it would select between hot and cold air for the side vents perfectly, but after a few months it would only blow hot air.

I thought that the Duo-valve may be at fault, because I had the same problem on my last W124; the brass plunger had snapped off its arm, and I fixed it by rebuilding the the duo-valve.

So the other day I took the Duo-valve apart, but everything appeared to be in good order, so I put it back together and tried it again, but I'm still getting hot air.

Is there anything else in the system that could be faulty?

 

[joe1972]

Hi there.
I had the same problem with my W124 E300d. The duovalve ended up being ok. however, with mine it was a pinched/broken wire from the control box.
The solution was I read on another thread that Television posted that 0v is read with the dial controls set to hot, but you should look for around 8v coming through from the control box (to the duovalve) when the dials are set to the coldest/blue setting.
I was getting frustrated as the valve appaered to be ok, but thats how I found the problem with mine from that previuos post.
Hope this helps?

 

[television]

Check as in Joes post above,, the pulsed voltage will show about 8v when the dials are set to minimum

 

[MercStraight6]

Thanks. I checked the terminals on the Duo-valve today and neither side was open circuit, so I think they're ruled out now.

I'll check the voltage on the plug tomorrow.

 

[Alex Crow]

do a resistance test of the two coils, they should be 12 or 16 ohms. the control unit has an over current cut out and will stop switching the duo if it sucks too much juice.

 

[MercStraight6]

do a resistance test of the two coils, they should be 12 or 16 ohms. the control unit has an over current cut out and will stop switching the duo if it sucks too much juice.

I've finally got round to investigating this, and found that:

1) There is no voltage going to either side of the duo-valves, with the engine running and the dials set to hot or cold.

2)Both coils showed 17 ohms resistance.

I think it's probably a faulty control unit, part number A1248302585.

 

[television]

Quite a few being broken so not too bad,,I could take a look at it for you,,but no guarantee of a fix