A/C sometimes works, sometimes doesn't.
 

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?

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

Al,

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

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

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.