Air Conditioning - Outside unit wont do anything

I am about to gie up and call a repair guy, but before getting knee deep into an expesive bill, I come here for tips first.

Last fall, i put in a new TStat (digital)..worked great. then we shut it off for a week. When we turned it back on Cool at the end of the fall, the outside unit did not kick on, but the fan inside the house ran. No sounds of the compressor clicking and the fan itself never moved.

I know its not the wiring to the tstat and I am thinking compressor or conensor fan motor. I am getting the proper volts to the wires incoming and outgoing. There is a black button type thing (the contactor??) that when pushed, it sounded like the compressor would HUMM.....but then I let go and it would stop. Of course, it doesnt even do that anymore...that fan in the unit still has not moved.

How in the world can I diagnose this problem? I dont know much about these,, but I know if the power to the AC is off, I am willing to try anything......by the way, it is a Rheem from 1990.

Thanks!

Pretty straightforward electrical testing.

Make sure your circuit breaker or disconnect outside, is in working condition, to allow the passage of the 240 volts.

With a voltmeter, you test to see if when you turn the stat to cool, that you have 24 volts out there to the contactor. Then you want to also find out if you have 240 volts to one side and 240 to the other side.

If the contactor is not closing on it's own, you either are missing 24 volts or the contactor is shot.

I have verified that the voltage is where it is suppose to be and all contactors are working. What would you suggest next?

Do you have electircal wires connected to the copper lines? If so, these would be a pressure switch(s). This/these will incapacitate the operation if low on refrigerant. See if you have that/them.

After this visual, I'd move on to seeing if the fan wires ohms out okay. If so, I'd suspect the capacitor. Capacitors are only like $10 at the motor shop.

its pouring right now, so cannot look in the box again until later. But based on what I remember, no copper lines in the junction box outside, just black electical wires and a ground.

When checking ohms on the fan wires, I am assuming I need to remove the top of the unit, correct? Either way, it will have to wait probably a day until I can get back in it once the rain subsides.

Also, are there national stores that carry these tpyes of parts or is it going to be a a local shop for things like a capacitor?

Thanks

its pouring right now, so cannot look in the box again until later. But based on what I remember, no copper lines in the junction box outside, just black electical wires and a ground.

When checking ohms on the fan wires, I am assuming I need to remove the top of the unit, correct? Either way, it will have to wait probably a day until I can get back in it once the rain subsides.

Also, are there national stores that carry these tpyes of parts or is it going to be a a local shop for things like a capacitor?

Thanks

Copper lines I refered to - I meant freon lines coming and going from the compressor. I wanted you to see if you have any sort of electrical switch connected to the copper tubing.

You do not have to remove the top of the unit(I don't believe). You should be able to trace the fan wires to where the ends are connected at a side entry area where the contactor and capacitor is, and unhook the fan wires from those locations and test.

Moderate size and larger cities have mechanical supply houses that carry parts for certain brand HVAC equipment, electrical and plumbing components. You also can get motors and capactiors at a motor shop. Look in your yellow pages. If you live out in Tinbucktu, you can always order stuff over the net, also.