A/c Not Working Toyota 1994 - Pre-1997 Toyota Corolla and Geo Prizm

Looks like I have an electric problem that prevents my A/C from working. When I press the A/C button, the light comes on but the compressor is not engaging. I use to have this problem on and off last summer but now A/C never works. Bizarrely, when I press off the A/C button and leave the fan on, my engine start running faster (like it should do when you put the A/C on !). My A/C was repaired last year(new compressor, new condenser). My mechanic sees no problem with the A/C itself and refers me to an electric shop for an electric check of the A/C and fan circuits. Did someone had this problem and can clue me on this?

Thanks

Could be the magnetic clutch on the compressor is not engaging. Could be as simple as a loose wire - unit is not getting power, so it doesn't turn when you press the A/C button. Sometimes if the system is low on refrigerant - it will act intermittently. Could be any number of wiring issues as well - though, not as common. If it is an electrical gremlin - could be tough to trace down without a factory service manual and full wiring diagram.

Thanks for your comment

I really think there is an electrical problem here. Refrigerant is full. What is strange is the fan inside the car. When I engage the fan, without the A/C button on, RPM of the engine picks up about 400 or 500 turns. If I then press the A/C button on, the RPM goes back to what it was before I did put the fan on ! So looks like the link between the A/C button on the fan is working unproperly. Just putting the fan on should have no impact on the RPM of the engine.

There is an idle-up circuit that pops on when you engage anything that could put a heavy load on the engine (doesn't mean that the load is there - just that you closed a circuit that is wired to a heavy load). So that means part of the circuit is functioning correctly - trick is to find the bad part of the circuit. You can do it brute force method - tracing all the wires back from the switch to the device - use some taps to check for continuity in the lines, etc. Depends on how much time you want to spend on it.

The High/Low refrigerant switch could be defective....sensing a low refrigerant condition even though the system is full. You can jumper this switch and see if the clutch engages to spin the compressor. Also check to see if you have 12 volts DC at the compressor clutch connection.

Looks like I have an electric problem that prevents my A/C from working. When I press the A/C button, the light comes on but the compressor is not engaging. I use to have this problem on and off last summer but now A/C never works. Bizarrely, when I press off the A/C button and leave the fan on, my engine start running faster (like it should do when you put the A/C on !). My A/C was repaired last year(new compressor, new condenser). My mechanic sees no problem with the A/C itself and refers me to an electric shop for an electric check of the A/C and fan circuits. Did someone had this problem and can clue me on this?

Thanks