I have no heat because there is a constant current going to my mono valve keeping it closed. All the posting I’ve read said that as a fail safe, the CCU should fail in a mode that supplies heat if the defrost button is pushed before engine start up. This is not the case for me. No matter what buttons are pushed on the CCU, I continue to get a current to the mono valve keeping it closed. I have been driving around the last few weeks with the electrical connector disconnected on the mono valve so I can get heat. All the other functions of my CCU work. The temp dial operates to turn on the A/C as its supposed to. The blowers and vents are all working properly. I pulled the CCU and re-soldered the potentiometer connections, and a few other connections that looked suspect. There were no burn marks on the PCBs as other posts said was indicative of my aux water pump burning out. The aux water pump is working. Is there a temp sensor I should check that monitors the coolant temp and then tells the CCU that the coolant is hot enough and its time to open up the mono valve?

Years ago I found a broken solder connection that was associated with the temperature control wheel.

Thought I'd reply... just to give you hope and to let you know that someone cares.

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Earl



1993 190E 2.3
2000 Toyota 4x4 Tundra

jr -

Heat has been "intermittent" lately (mostly NOT). My monovalve is in OK shape I but haven't pulled the connector on it. If that gives me heat, I guess its time to pull the console apart to see if ej's fix takes care of it. Intermittent kinda sounds like a bad connection (cross fingers, knock on burl wood).

Its not a critical issue at the moment because its been on the warm side here but I don't think the spousal unit will put up with it for long (good thing the seats are heated! )

I have too much going on to look at it very soon (if it gets really cold, she can drive something else) - I'll watch the thread to see what you find.

Kevin

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"Dangerous with a wrench...and not smart enough to know it"

Stable (in order of acqusition):
'84 500SL, 280SEL (Euros)
'77 280SE. '90 560SEL
'79 450SEL 6.9,
'95 C280 (totalled by daughter 8/07)
'81 280SL (rescued) '88 300CE
'86 560SEC '95 C36
'01 CL55

DD's: '04 S500 4Matic (SWMBO)
'04 F150 Crew