The aux fans should come on with high pressures on the A/C. If over 240, the fans should be on. To check, just bridge the two wires at the drier that come to the red switch. (I hope you have a red switch, it could be green, if so, it should be updated).
If the fans work, the other switch should be checked. It has two functions. It will open if the pressure drops too low, but it will also open if the pressure in the drier is too high. I have seen these malfunction.
To check, you have to find the input and the output. You probe the output and watch. If the compressor turns off and the signal is there for on, you have another problem..(like the compressor control unit.)
It goes like this. pushbutton-drier switch-compressor controller-compressor. This is the logic chain.
1992 500E (very soon I hope
1981 280GE SWB
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