OK, ac unit {trane}worked fine for the first couple of days except contactor had a buzzing sound louder than normal. One day, out side unit wouldn't kick on just loud buzz from contactor. I purchased a new contactor and the smaller capacitor, contactor was kicking in, still nothing only a slight humm. So I did some reading on this wonderful web sight and started checking all my volts. Discovered I was only getting 110 off one side of disconnect , the other side had a low voltage. The disconnect breaker was bad, so luckily I had a 60A breaker and installed it. Went in and turned on stat looked out side, the fan is blowing on ac unit. I thought Sweet! anyway noticed the compressor is not kicking in. both sides of the contactor are reading 115v, one side of the smaller capacitor is reading right side 215v the other side reading115, the bigger capacitor reading right side 115v and the left side reading 140v. Could this breaker going bad cause damage to something else? Maybe the larger capacitor? The hvac store is closed today.my guess is the bigger capacitor is bad or maybe low on freon.

If you read across the contactor when activated you should get 220-240 volts. Check that first.
Turn off power and check the terminals on the compressor itself. There should be 3 wires and they should be attached to the compressor. The lid that covers the wires on the compressor can be a bear at times to get off. Make sure you replace it before starting the unit.
Repost here with the results.

OK, you say read across the contactor when activated I should get 220-240, do you mean each terminal reading 220? On the contactor T1, L1 reading one at a time I get 115v, so your saying each one separately should read 220-240 and I am only getting 115v what could cause this? I will check the volts at the compressor. And post back

You test across both hot legs on the hot side of the contactor. 115 and 115 = 230. Your A/C runs on 230 volts

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Originally Posted by DENTBGONE

ok, ac unit {trane}worked fine for the first couple of days except contactor had a buzzing sound louder than normal. one day, out side unit wouldnt kick on just loud buzz from contactor. i purchased a new contactor and the smaller capacitor, contactor was kickin in, still nothing only a slight humm. so i did some reading on this wonderful web sight and started checking all my volts. discovered i was only getting 110 off one side of disconnect , the other side had a low voltage. the disconnect breaker was bad, so luckily i had a 60A breaker and installed it. went in and turned on stat looked out side, the fan is blowing on ac unit. i thought Sweet !, anyway noticed the compressor is not kickin in. both sides of the contactor are reading 115v, one side of the smaller capacitor is reading right side 215v the other side reading115, the bigger capacitor reading right side 115v and the left side reading 140v. could this breaker going bad cause damage to something else? maybe the larger capacitor? the hvac store is closed today.my guess is the bigger capacitor is bad or maybe low on freon.

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OK, I tested again at contactor yes I have 115v and 115v. I haven't checked the compressor yet was wonderinghow to access these connections. The wires go in the bottom of the compressor, I see a very small plate around the wires very hard to get to, is this where I access the leads or it looks like the top comes off not really sure? Another thing is my stat wires on contactor one has 24v the other one not reading anyting, are both wires supposed to read 24v?

Across the contactor low voltage terminals should be 24 volts when calling for A/C

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Originally Posted by hvac1000

across the contactor low voltage terminals should be 24 volts when calling for A/C

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I have 24v on one of the low voltage wires. One reads 24v and the other reads no voltage. What could cause this? Thanks for your help.

If you have 24 volts across both wires that is what you need.

I am sorry for the confusion, I have two low voltage wires coming into the unit right? Mine being white and one being red both very small right? If I test these wires one at a time separately I get 24v on the red wire and no voltage on the white wire. You are saying each one should read 24v, is this correct? If so could you tell me why I am not getting 24v on the white wire. Thank you.

NO if you attach one of your meter probes to the red wire and the other meter probe to the white wire you should get 24 volts. Good night

OK, bingo now I got you. I did as you said and yes I had 24v. Now I didn't test the big wires on the contactor earlier like this, just one lead to one side and one to the ground. So I tested the T1 and L1 one probe to each and got no volts had a minus- sign on the left side of the 0.00 fashing. This is what you told me to do earlier in the post I assume. Sorry about that. If I test one probe to L1 and grounded the black probe I get 115v, same for T1 side. As far as crossing them over when activated nothing. Thanks again

If you cannot get 220 to 240 volts on the line side of the contactor without the unit running you have a power/voltage problem. If you cannot get 220 to 240 volts on the contactor on the load side when attempting to run the unit you have a power/voltage problem. It's that simple.

I tested the contactor again this morning, I get 220/240v crossing the contactor, ac not activated. When turning on the ac unit and crossing over contactor I get nothing, if I read the probes one at time while ac is on I get 115v on the line and 115 on the load side. I have a volts problem, OK could you tell me a couple things that might cause this?

You have one of 2 things happening.

First if your contactor is not pulling in (kind of a snap sound) you have a low or non existent 24 volt control power source. If you have 24 volts across the two wires that activate the contactor then the contactor coil is bad and it is time for a new contactor.

If you have 220/240 volts on one side of the contactor and when activated as in turning the A/C on you have no 220/240 volts coming out of the contactor you have a defective set of contacts in the contactor and it will need to be replaced.

Now if the contactor is not activating at all you will have to trace the low 24volt wiring.

First you will need to look at the wiring diagram that is on the blower door of the outside unit. See if you can locate and high or low pressure switches OR anything in the 24 volt line that could stop the contactor from working. Most units no longer have these features but you need to look anyway.

This is all I have on this subject. Good Hunting.

Thank you, very helpful. My contactor is new and the contactor is pulling down clicking. Contactor is not exactly the same as old one.they cross checked the number of old one. Old contactor sticker reads 24v 50/60 that's all I can read. The new contactor reads 40A 600v 24V coil, 1 pole. Does this mean my old one is 50/60a and my new one is only 40a? I have a 60a disconnect. Now ac switch turned off I get 220v crossing over the contactor{not just one side one probe to L1 and one to T1] when the ac is switched on I get no volts crossing over the contactor. Ac switched on, test probe on L1 the other probe grounded I get 115v same for T1. You said the contactor, could this be the wrong contactor? I see no kind of switch. I do see a small thing with two red wires clamped on the small copper line coming from the compressor. The unit has two capacitors, a cf fan capacitor, I replaced this when I replaced the contactor. The other cr run capacitor, which hasn't been replaced. This is tuff but I got to be close.

I already explained the voltage problems to you both high and low. If you cannot find any broken wires and if the compressor terminals are all connected it should start up. I believe you will be best served calling for professional ON SITE service. This way the service person can see what you have done to your unit and make corrections for the mistakes.

It is also possible that you hooked up the wrong wires top the capacitors you replaced and that will also cause problems. We seem to be going in circles so I can be of no further assistance. Please call for on site help with your problem I am out of possibilities. Thank you