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1980 300D
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309 Posts
Discussion Starter #1
Help! My 1980 300D has no coolant in the AC system - I'll be performing leak tests this weekend - but when I dial the temperature down low and turn on the climate control, AC off, heat blasts from the vents. Is my heater servo fouling up? Should my heater core be so ready to heat all the time? When I get the AC to work, won't this hot air defeat the AC? Is this a monovalve issue? Does my car even have a monovalve? Anyone else have similar situation? I'm in SoCal and it is AC time...
 

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Premium Member
W-1-2-3 Go!
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16,161 Posts
I just had my AC recharged. I would assume you mean refrigerant when you say "coolant"? If so then it's not cooling anything so naturally, warm air blows out the vents. If you didn't do anything lately (nothing was replaced at all w/ AC system) you might want to check for leaks. Same thing happened to me--no refrigerant, so warm air blows out the vents. BUT in cold days or at night, cold air blows out the vents if switched to EC (outside air)...

By the way, where in SoCal are you? I felt the same heat you're feeling...I think I lost weight lol
 

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1980 300D
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309 Posts
Discussion Starter #3
The air coming out of the vents is super hot - like the heater on full blast. WTF? In addition to the dreaded heater servo, which I replaced last year, is there another valve that would keep the heater core molten?

I'm by the ocean so I don't need the AC except when east of the 405...
but would like to clear up heasting situation before fixing and charging system and ending up with lukewarm air.
 

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96 E300D
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817 Posts
There is two other components of the heater, the sensor located behind the right speaker and the "computer" located next to the sensor. Either of these will affect the heat.
 
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