1980 300D. Working aux pump, newer aluminum body servo.
Assumed working (not fried) control module behind glovebox.

New A/C compressor and several replaced vacuum pods.

So worked great all winter. Cabin stayed warm when it should.
A/C does cool off car, worked good at end of summer last year.

Noticed that when A/C compressor is switched off that cabin vent
air is hotter than outside air.

Unplugged auxiliary water pump (was going to put a ball valve on the
water line next) and noticed cabin cooled off and vent air is now same
temp as fresh air outside.

My assumption is that aux pump should stay off when heat is not needed.

So, anyone have a similar problem and solution ?

Anyone have the short and easy method for testing the ambient temp sensor,
cabin sensor, and sensor in the air box ?

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250

I think the aux pump should stay off unless you have the heat on, and your temp wheel is set low, and the next to right button, EC is pushed in, that way the AC won't come on either. The temp sensor is either that small square grill on dash, or if you don't have that, it is located under passenger speaker. There is a hose going to the one on the dash, anyway, one section is made of foam that has a tendency to deteriorate. Think you have to pull glove box, but feel around behind if you can first.

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83 SD

84 CD