Unit blows heat whenever I am moving uphill or revving to speed. Otherwise, the AC seems to work just fine, however, the heater does not seem to be controlled by the thermostat at all. Any ideas to share and point me in the right direction? Regards, MW

The thermostat controls the folow of anti freeze into the engine, when the when a certain temp is reached the thermostat opens to cool the engine. The heat is usually controlled by a Servo, or some other device. which allows hot anti freeze into the heater core and the core is where you get the heat from. As far as you problem, sounds like your servo or whateven the 190 used to control the heat and AC is not pumping and going up hill the laws of gravity take over. have you had your anti freez changed lately? there could be air in the system. The AC is a separate system from the heat even thou the same medhanics control both/

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Al Lueb
1999 C280 54K miles
1979 450 SLC 144K miles

Mine did that, it took me a while to figure it out, mostly because my 190E is the first gasser I've had in a very long time. Diesels have no vacuum so they have a separate vacuum pump, which means the throttle position has no affect on the vacuum, for what that's worth.

First, your problem is a vacuum leak. When you've got the throttle open (like when you're going uphill) the engine vacuum drops. There's a check valve that keeps the car's vacuum up, but you've got no vacuum supply if you need more. If the check valve doesn't work or you have a leak you'll loose vacuum.

Second is why. The loss of vacuum default for the climate control is heater on and defrost on and all the others off. I had two leaky actuators that took a little bit to identify and change. A test of all the actuators, except the heater valve actuator, is to select defrost (single up arrow). That will command all actuators to their relaxed position, except the heater valve. If that keeps the heater from coming on when you're going uphill its one of the other actuators. If not, start hunting, it could be anything.

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5 speed '91 190E 2.6 320,000 mi. (new car, fast, smooth as silk six, couldn't find any more Peugeots)
5 speed '85 Peugeot 505 2.5l Turbo Diesel 266,000 mi. (old car, fast for a diesel, had 2 others)
5 speed '01 Jetta V6 (new wifes car, pretty quick)
5 speed '85 Peugeot 505 2.2l Turbo Gas 197,000 mi. (wifes car, faster, sadly gone just short of 200k )
5 speed '83 Yamaha 750 Maxim 14,000 mi. (fastest)
0 speed 4' x 8' 1800 lb Harbor Freight utility trailer (only as fast as what's pulling it)