You can jump the switch to test if it's working. Probably not a good
idea to leave it jumped if's bad. It's there for a reason, most
likely to protect the compressor. On a '91 DX it's on the drivers
side someplace near the canister with the viewing glass.
I tried jumping my sensor years ago to see if there was too little gas
for the compressor to work. When jumped the compressor worked. I
then filled the system (converted to r134a) and worked fine for a few
more years when I had to refill again. It's not worth it for me to
fix such a small leak on such an old car.
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