A/C sometimes works, sometimes doesn't.

[Greek55]

I am trying to figure out why my air-condition sometimes will cut on fine and other times I cut the fan switch on and nothing happens. I have run 12 volts to the compressor and evaporator fan and both work. All fusses and relays check out fine. Right now, nothing happens when I cut the fan on.
What tests do I need to run to figure this out?

[al lkosmal]

Often there is a low pressure switch and high pressure switch in the AC system. If either of them trip, they may cut power to the compressor clutch. If you know your way around a Multi-meter, you can check if these switches are open or closed, during operation. However, the switches typically trip to indicate a fault. Low pressure can indicate a system leak and/or low charge, high pressure may indicate blockage, etc....so just replacing switches may not fix a problem. Also....your compressor clutch may be zapping out....either shorting to ground or open. Measure the resistance across the clutch wires. If I remember the resistance will be between 2.5 ohms and 5 ohms. If above or below...it may be clutch time. Also check the continuity of the 12V supply from the thermostat all the way to the compressor. That's all i know...maybe an ac expert will jump in.

regards,
al

[Mitch Leland]

Al,

Do you know for a fact that your system is charged with adequate refrigerant?

[pete3799]

What Al said.
Also check the relay in the smugglers box.

[wwest]

Originally Posted by Greek55

I am trying to figure out why my air-condition sometimes will cut on fine and other times I cut the fan switch on and nothing happens. I have run 12 volts to the compressor and evaporator fan and both work. All fusses and relays check out fine. Right now, nothing happens when I cut the fan on.
What tests do I need to run to figure this out?

I'm pretty sure that for an '83 the only compressor clutch control cycling is the thermostat's capillary tube/bulb. Used to "sense" the temperature on the face of the evaporator. Not altogether unusual for those to fail in a manner, switch contacts AT the thermostat itself, that result in no compressor operation.