83 300SD

I can't get the AC to blow cold air only hot. I've replaced the monovlave and every once in a while everything will work great and the AC works fine. But these occasions are getting further and further apart. I can punch buttons and get it kick on the AC, but after a while its back to hot air. The climate control unit will constantly click, click, click click by itself at about 3 times a second. I recently bought a used climate control unit off of Ebay and took it apart and inspected all of the solder joints (whick looked good) and it does the exact same thing. Did I buy another broken climate control or is there something else causing the thing not to work properly?

Anyone?

Check the aspirator hose from the in-car temperature sensor. If its fallen apart or is disconnected, the climate control will not read cabin temp and could do this. Remove the glove box liner to locate this hose. I think the hose goes to the sensor mounted by the right dash speaker , but please understand I own a 123 and my hose is routed to just above my center dash vents but performs the same function. Hope this helps

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

I ran into some issues on the SD with the auxiliary water pump. If the pump doesn't operate or draws too much current, the CCU will have problems with this and, in some cases, will fry a component on the board.

Disconnet the aux. water pump and see what you get. There is a connector plug that is just to the inside of the battery. Unplug it and see if the symptoms go away.