My 91 was converted to R134 before I got it and worked well, then worked erratically. My then mech who has now moved away did a solder job on the circuit board in the dash controller and that was effective for a while, but he said I should get another controller. I did and have now put it in and immediate success that day and the next, actually had to turn it down when in high 90's heat the other day, it was too cold. But the next day it worked at first, drove around a little bit, then restarted the car and nothing, no cold air. The fan works.
Today I tried it while parked, not driving. There was cold air at first in fan position 1 and 2 and I could hear the compressor engaging and disengaging. Then it stopped. This may have been coincidental with trying fan position 3 but I'm not sure. But before it stopped I noticed that the speedo, which has been behaving erratically lately, and of course should not be moving while parked, would jump to about 40 mph when the comp engaged, then drop back down to 0 when it disengaged. But then there was no more air and no more comp engaging, and no more speedo jumping. Any ideas?