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Old 07-10-2004, 02:57 PM
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Join Date: Oct 2001
Location: Dallas, Texas
Posts: 19
1986 420 SEL Climate Control

saw this posted on another site - with no answer and have the EXACT same situation - any ideas?


... Help Please!!
I have a 1986 420 SEL with 116,000 and the climate control is erratic. Hopefully someone has experienced or heard of this complaint for some possible direction:
(1) When I turn the vehicle climate control on A/C, it takes about 15-20 minutes before it starts to blow cold then at will, it will blow warm or ambient air, then will go back to cold and vice versa.
(2) If I have the button pushed in for dash vents only, the air will blow out of both the defrost and dash vents at will. I did notice that when I am accelerating or at freeway speeds, 90% of the air blows out of the defrost. When I am at idle or stop and go traffic, it blows out of the vents. Is this system on some type of vacuum??
(3) If I start the vehicle when cold (the climate control is off,ie the button "O" is pushed in, the blower still comes on for a few seconds or so at will. I did notice if I push the "O" button again, even though it is pushed in, it will shut off. ...

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Old 07-10-2004, 03:05 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Item 3 is probably the only sure bet. Because it could also effect 1 and 2 I'll give my opinion on it first.

The pushbutton control is most likely thye cause of item #3 and could easily be the problem in #1 also. Too large of an airgap on the compressor clutch is another answer to #1.

On #2, yes this is vacuum controlled and the relationship between freeway and idle says that either the supply is weak or the leaks in the system are small enough that a huge source overcomes them.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 07-11-2004, 01:53 PM
Registered User
Join Date: Oct 2001
Location: Dallas, Texas
Posts: 19
Thanks, Steve - I will begin the the process - many thansk for the direction and your time to respond!!!

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Old 11-08-2004, 10:45 PM
Registered User
Join Date: Oct 2001
Location: Dallas, Texas
Posts: 19

Removed the Climate Control Unit (CCU), resoldered the the three pins holding on the wheel potentiometer to the circuit board...WORKS like new!!! Spent in excess of $1000 at dealerships and they could not fix!!! Thanks to this website, about 90 minutes of time - DONE!!

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