A/C not engaging

[juggernaut2874]

My 94 XLT A/C is not engaging all of a sudden. The A/C light by the console switch lights up and the blower fan is working. The A/C-WOT relay in the power distribution box keeps clicking or cycling. I replaced it with another relay but it did not fix it. Could it be the clutch, or switch? Any ideas?

 

[Alan_V]

For starters, backtrack from the condensor and find the connector. With the A/C switch and fan ON, check for B+ on one wire and ground on the other. If you have B+ on one wire and a ground with < 50mv on the wire, the circuit's good. You can prove it to yourself with a test light in place of the condensor. If all's well, then the clutch could be a good possibility as they will wear over time.
If you don't have good power and ground, then check at the relay. You need a decent circuit diagram to know where power should be.

 

[BrooklynBay]

Did you see if it needs to be recharged with freon?

 

[juggernaut2874]

Would being need to be recharged keep the A/C from enaging and cause the relay to continuously click? I will connect some test gauges to the ports to see the freon level and go from there.

 

[gsmaclean]

Yes. If you have no or low refrigerant left in the system, the pressure switch will disconnect the compressor clutch so that it won't engage and rotate the compressor, because the lack of lubrication (which is carried along in the refrigerant) will cause the compressor to self-destruct.

This is also why it is a bad idea to just bypass the pressure switch to force the compressor to engage just "to see if it will fix the problem."

 

[juggernaut2874]

Thanks for the pointers guys. I'll check the refrigerant level first and go from there. I'll let ya'll know what I find.

 

[juggernaut2874]

Refrigerant level good to go...roughly 45 psi at max A/C. Disconnected the connector going to the A/C low pressure switch and shorted it out temporarily to see if the A/C clutch would engage. It did engage so I removed the short and re-connected it. The A/C continued to work like normal for the rest of the day even after turning it off and on several times. Thought I must've shocked the switch into working. This morning it was back to not working at all. I assume the A/C low pressure switch is bad. Am I on the right track?

 

[BrooklynBay]

You could check the switch with a continuity tester.

 

[juggernaut2874]

Problem fixed! It happened to be the low pressure switch being bad. Quick replacement for 12 bucks and it works fine.

 

[BrooklynBay]

Thanks for the update!