1987 GXL, Factory Air.

Blower used to work, AC light used to come on, compressor clutch would not engage. This was a 1:00 pm today.

I traced back to the pressure switch. It was open. I check pressure, it was low, 10 psi, that is another problem for later. One line had 12 V on it, the other did not. I bridged the pressure switch wires to do a quick system check and the relay did not switch. I put 12 V on each of the legs of the sensor and grounded each leg (for a second). I thought I was dealing with relay logic. I heard an odd buzzing sound and decided this was a bad idea. It turns out the wire from the computer, to the pressure switch, is the one with 12V on it. I did not expect this. This is the blue wire with an orange stripe.

Now it gets weird. Before all of this, when I pushed the AC button on the dash, the light came on and the fan worked. Now the light does not come one and the fan is dead. All of the mode control switches seem to work, and I can hear things move in the dash when I press them.

If I pull the relay, and put 12 V across the control lines, it work. You hear a nice snap. All fuses are good, all circuit breakers are good.

I have convinced myself I do not understand the control logic. I will spend the evening digging through schematics and isolating systems. But, if any of you happen to know the answer, I would really appreciate a reply.