Wierd problem here. When I turn the AC on my cooling fan does not come on. The fan operates normally to cool the engine however. From the wire schematics it looks like the pressure switch goes open when under pressure. I tested it with my meter and it is closed when at rest and it goes open when under pressure. The deal is that when I ground the blue wire the fan comes on. So if I plug the pressure switch in, the fan comes on. Not sure why this is. From what I've seen the fact that I have an '89 chip should not matter, the input into the ECM is the same for each year and the pressure switch operates the same as well. Anyone know something I am missing here?

 

The switch is normally open and closes (thus creating a path for ground in the circuit) when the A/C is pressurized. Perhaps you have an incorrect switch?

 

Thats incorrect. I wiring schematic says otherwise and I tested it myself as well. The pressure switch in the line on the passenger side front frame rail is normally closed, and it opens above 233psi. That is what the schematic shows and thats what it did when I checked it with my ohm meter. the switch is the original one to the car as well. What is interesting is if I ground the blue wire the fan comes on.

 

Yes, I believe you are right, however, my haynes doesn't have a blue wire in the fan circuit. My 89, the a/c switch is the same as yours, however, the coolant fan switch works opposite while they are parallel into the relay. Doesn't make any sense to me. I'm thinking it is a misprint. According to Haynes, 1988 and on TBIs had a normally open a/c switch. If I still had my A/C I would double check for you.

It appears the ECM is in series to your A/C switch, mine is not. The chip still may have an effect on its operation.

 

Well if I could find an AC pressure switch that worked opposite of mine I'd be set to go. You say the TBI stuff has a pressure switch that is normally open and closes under pressure? I'll have to start checking that stuff out.

 

Check the wiring, dude.



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Jerry
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