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AC - bad start?

1990 T-bird won’t start if AC is on, but will run OK once started with it on. You have to turn off the AC every time you start the car.

Some older domestic vehicles do this. The AC is not bypassed by the ignition switch as it is on today’s vehicles. I had a 93’ Bonneville that did the same thing.

It is bypassed on this car. In fact, the compressor is controlled by the PCM and it won’t turn it on until stable idle is reached.
The OP has some sort of electrical problem related to the AC demand input to the PCM. I have heard of this before, but I don’t know what the solution was. I would start with a trace of the wiring from the AC switch to the PCM. I would also check the AC inhibit relay from the PCM (maybe it is stuck closed).

The AC inhibit relay makes sense. I have not seen this problem on imports like Toyota, Honda, Nissan or Mazda. I have seen it on Ford, GM and Chrysler products a few times. I may go looking for a relay the next time it happens.