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3 Posts
Hi,
Did you fix your problem? I've found several postings about this all over the internet. I have the same problem. Apparently the engine coolant circulates through the heater system constantly by design and how much heat is put out of the vents has to do with the "blend air doors" which are vacuum operated. I actually just signed up for this forum to try to find troubleshooting advice for this very problem. Some people have suggested a faulty "blend air potentiometer". I'm not sure of the location of this, however I beleive the interior temperature sensor is located in the ceiling near the courtesy lights. Good luck and let me know what you find.

John Gregory
[email protected]
 

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2000 S500
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26 Posts
There's some sort of potentiometer under the dash that's supposed to be a real PIA to get to...my climate control has a poltergeist in it too...it just quits for about 5 minutes, then it works again...it's sporadic. When I accelerate hard (economy gauge all the way red) the air switches from floor to defrost vents and as engine speed decreases it goes back to the floor...I'm sure that part is vacuum related.
 

· W201, W202, W203, W204, W205 Moderator
Amethyst 2001 C320 with 363,000 miles
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1,755 Posts
lol my climate control system had a poltergeist too until I replaced the cold water temperature sensor (located near the firewall on top of the engine. It's a green two posted sensor that has a tendency to have one of the posts break pretty easily. In fact, when I had a new engine put in, the mechanic broke it because it is right next to the engine lift bracket, and his hook snapped it off. Unfortunately I didn't know until after the job was done, and I ended up replacing it myself.

However, that part is only about $15 used from a junk yard, and now my climate control works well.
 

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1985 2.3 16v euro
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35 Posts
a loss of vacuum supply causes the system to switch to the failsafe which is the maximum heat to windshield. you have roughly 18 inches of vacuum at idle but not so much at throttle, especially full throttle. have you checked your vacuum storage?? the lines get old and crack sometimes. you might hook up a vacuum pump and check them. as far as the poltergiest you might be tripping a circuit breaker?
 
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