AC Compressor Low pressure switch-1987

[Skeebaru]

I'm troubleshooting AC system. Press AC switch, compressor turns on for 1-2 sec, then shuts down. Electric engine cooling fan DOES NOT turn on. I thought this fan should come on when AC comes on. I'd like to jump the two wires for the AC low pressure switch and check the compressor. Two questions:

1. Where is connector to low pressrue switch

2. Is there a relay which may have gone bad (causing the fan not to come on and therefore the compressor to remain running)?

1987 4 x 4, Turbo, GL 1.8 MPFI

[john in KY]

You should have 2 relays mounted on the passenger-side strut tower. The switch is mounted down low on the passenger-side of the radiator.

[Skeebaru]

I went to the parts store and on-line to look for a ac compressor relay. Once I had that part I visually matched them to 4 relays above the fuse block in the car under the steering column. I'm not sure which of the 4 are the ac compressor relay, but at least I got it down to 1 of 4.

 

I think I've located the low pressure switch on the drier. The darn thing has 4 wires on it,... which 2 do I jump to check the compressor for operation?

[Skeebaru]

OK, more details in case someone can help. The four wires are: 1. blue/wht stripe, 2. blue/black stripe, 3. red/wht stripe, 4. blue/red stripe. I don't want to jup the wrong wires here.

[presslab]

What is the static pressure in the system? It's much more likely that you don't have refrigerant in the system rather than the switch being bad. The compressor coming on for a second points to this as well.

[Skeebaru]

I'll have to get some gauges on it again,..last I checked I think it was 80 psi. What would answer why the electric fan does not come on when the AC button is pressed? I tried replacing the AC compressor relay already, no luck.

[presslab]

I'll have to get some gauges on it again,..last I checked I think it was 80 psi. What would answer why the electric fan does not come on when the AC button is pressed? I tried replacing the AC compressor relay already, no luck.

 

Yeah check the pressure when the compressor kicks on. If the low side goes too low (normal should be around 30 PSI) it will turn the system off.

 

I'm not sure if my wiring is the same as yours, but it looks like blue/red and blue/white are for the "econo pressure switch" that engages the fan relay. I don't know what pressures this "econo" switch works at, but if this switch is not tripped it will not trigger the fan relay.

[Skeebaru]

From a previous post I read about with a guy with AC problems on an 88 DL, there was a reply that suggested the black sensor on top of the compressor (belt protection system) could be causing the problem. The suggestion was to jump two red wires behind the glove box. So I did this, compressor came on and stayed on. Nice cold air,...however after some time I heard clicking noises coming from elec fan area and screeching from compressor (loose belt?) AND the compressor would not turn off! as if I was jumping the low pressure switch. So, I figured that avenue was wrong. I still would like to test the low pressure switch next to the drier., but I can't figure out which 2 of the 4 wires to jump. When I google the low pressure switch, I get this 2 pole switch,...mine has 4 wires. Are there 2 poles behind those 4 wires? Needless to say I'm confused. I might go to a wrecker and pull a low pressure switch if for nothing else than disection. Anyway, back to your thought there appears to be enogh pressure.