Hello all,
I have been trying to find out some answers for my cooling problem. I have a Rheem A/C unit that as of yesterday has worked fine. When I switch my theromstat to cool I get the blower to start, but the outdoor unit will not fire up. I replaced the compressor contactor hoping that was the problem, but the new one chatters just as the last. Now, on to the weird part. If I check the voltage on the 24 volt side of the contactor, I get 24 volts if I check each side by going to the post and then grounding my tester. But if I check it across the contactor, I only get like 4 volts. Coming up to the outdoor unit I have 2 24 volt wires. ONe has 24v to it, but the other does not. Tracing this back to my indoor unit, the side that does not have 24 volts is connected to the "c" terminal of my board. Should both of these wires have 24 volts to them at the same time? Also to add, the side that doesn't have 24v, it goes to the compressor, (under a small sealed cap) then another wire comes back out in the same area, leads to a small box right besides the contactor. This small box is where the wires for the contactor comes from. I don't know if I made any sense of all this or not. I'm a plumber by trade, and I will say one thing, you hvac guys have to be pretty smart to figure this stuff out lol! Thanks in advance for any help the can be given to this problem. Charles.

I thought I would add, I can push the contactor down and the a/c unit will then come on. I don't know if this helps any or not.

There's probably something in your outside unit that's keeping it from running. If you're getting 24 volts out to the unit and only 4 volts at the contactor there's probably a control that's open. I think you are describing pressure switches on the compressor, you could have a low pressure switch and/or a high pressure switch. Hook one of your voltmeter wires to the wire that comes off the "C" terminal and take the other meter wire and check the other wire to each control until you no longer have 24 volts. They usually ground the c terminal on transformers so that's why you get 24 volts on the one line and not the other. C & the ground are the same polarity. You may want to look at the pressure switches and if there's one on the smaller line coming off the compressor, that will be the high pressure switch, sometimes they have a reset button on them that you can push in to reset.

I went back out to check and I don't see any other switches. If I follow the wires, the one from the C terminal goes to the top of the compressor, then another comes out, and goes the relay box. My neighbors are probably wondering what I'm doing outside with a flashlight at 11pm, hehe. Thanks for your quick response Jack! Charles.

Charles, I'm stumped, I don't know why the C wire goes to the top of the compressor unless there's some kind of high temperature limit switch. Maybe someone who's more familiar with Rheem can offer some suggestions. Normally the C wire runs directly to one of the contactor coil terminals on straight AC units. Sorry I'm out of suggestions..

You have a low voltage wire going to ground. Check the t-stat wire from the out side unit to the inside unit and the from the inside unit to the t-stat.(check for wires chewed by mice or smashed by ductwork or what ever). Also check the blue wires on the high pressure switch coming from the bottom of the unit to the contactor to see if it is up against the refrigeration lines.Also with the power off to the A/C and at the A/C undo one thermostat wire at a time at the wire nuts and put back. What wire makes it quit chattering?

It almost sounds like you're losing the common, I'm guessing "the box next to the contactor" is a time delay relay? Try removing both low voltage wires and test the together... if you still aren't getting 24 volts I would say it's a control voltage problem... at the control board on the furnace you have 2 wires that control the a/c one hooks to commonand the other goes Y... with the stat calling for a/c use you're voltage meter, one lead on the Y terminal and one to C- common if you have 24 volts you need to pull new wire to the out door unit

First let me say Thank You to all of my replies so far! I talked to a couple of HVAC guys today and got the same possible problem with the low voltage wire being shorted out. One guy who is a Rheem engineer suggested I check the time delay relay (YOu were correct in the guessing hvacservicetech_07) When I jumped from the load terminal over to my contactor, it closed and the unit fired up. Also after I checked the relay a bit closer I can see a bouble on the casing just under one of the common terminals. So I guess I will replace this relay and see what happens next? Let me know if this is a possible source of the problem, it might get kind of warm this weekend, lol. Thanks again guys!

It is very possible that is your problem. If it is the time delay relay I suggest replacing instead of jumping it. It is common for them to short out, they make sense but they can be a pain in the

Yes its possible the coil is shorted on the relay causing the chatter and not working. If it's a heat pump try the heating mode. If it works- reversing valve circuit.

Sounds like the control wiring(Shorted possibly).Disconnect control wires at contactor and at air handler. Do continuity check with(Usually 2 conductor, newer units have may be 5 or more for diagnostics. We will say 2)wires.
1. Open wires should read open at other end.
2. Connect one end with wirenut, other end should read continuity.
3. Verify no contact with ground.
Reconnect, or replace/repair

Good news! I finally got the system fixed yesterday. It turned out being the time break delay after all. Again I really appreicate everyone's help! Thanks a ton, Charles

Not a problem. We are here if you need us in the future.

I too had a chattering contactor. I could press down on the pull-down bar and the chatter would go away. The unit would come on and work, but chattered. I had 24V at the coil. I removed the unit and found a smashed bug between the coil and the metal pull-down bar. I disassembled the unit by removing four screws underneath. I scraped the smashed bug(s)and reassembled. Works like a champ now. Apparently, the extra gap created by the bug(s) was enough to cause the unit to vibrate and chatter.

I hope this helps someone.