AC Contactor and Capacitor wiring ? Fan running and breaker flipping.

Hi,
I could use a little help understanding the contactor wiring and figuring out why my fan is running with the inside unit off. And what might be causing my breaker to trip as soon as I set the unit to cool.

I have been reading through threads on here till my eyes crossed but cant find an answer that was clear enough for my exact situation. Though I know there have been a lot of similar issues posted.

This is a Trane XR12 (wasn't sure if this should be here or in heat pumps forum) had been running OK this winter and spring, has been a little on the loud side but cooling and heating fine. This weekend I went and turned on the cool after the unit had been off for a few days. The inside unit was blowing air but I eventually noticed it wasn't cooling, went out and the outside breaker had tripped. The breaker trips every time I try to send the cooling signal to the unit (I didn't try heat yet). Went out side and the outside unit would buzz when turned back on but then trip the breaker as soon as I set the inside back to cool.

Opened it up and the capacitor was bulged on top so I assumed it was bad and took it out and tested it and it was for sure bad. First mistake was that I did not take a picture of the wires on the capacitor before I removed it (that was dumb). Went and bought a new capacitor, the new one was smaller but the ac parts store guy said it would work the same the size didn't matter. Looked up the correct wires online and I am almost positive I have it wired back in correctly. Orange-Herm Brown-Fan Purple and red-Common


So then I went and turned the outside unit back on and the fan started running going faster then slower then faster. But the inside unit was set to off. I thought this was wrong immediately. Turned the inside to cool just to make sure and it tripped the outside unit breaker. This is was is happening now. Fan runs when outsides breaker is on, only turns off it I flip the breaker. Inside unit still slipes the breaker anytime I send a cool signal.

Could a bad contactor cause the weird fan running issue, or could it be that my wiring of the capacitor was wrong (or right but wrong if they wired something else incorrectly at another time)

The contactor doesnt appear to be stuck it moving up and down. But I ran out of time to throughly test it last night. I can tell you this. With the outside breaker on and the inside unit set to off I am getting 120v at the top of the contactor and 0 at the sides and 0 at the bottom. I thought this was odd as in my reading it sounded like the main power should be coming in from the bottom of the contactor. Also shouldn't I be getting 240v?



Thanks in advance for any help.

 

You should measure 240VAC across either the top terminals or bottom terminals and 0VAC across the other terminals when the thermostat is OFF. Don't measure from one terminal on the contactor to the chassis (ground), you need to measure between the top 2 terminals or the bottom 2 terminals. I assume that is what you have been doing, but I just wanted to make it clear. If you are only measuring 120VAC across one pair of terminals (top or bottom), you have lost one side of the power coming into the outside unit. There may be fuses in your outside electrical disconnect.

There should be a wiring diagram on the inside of the outside unit cover. Please post a clear picture of the wiring diagram and we can help you check if your capacitor is wired correctly. Is the new capacitor the same capacitance value as the original capacitor? The physical size doesn't matter, however the capacitance value does matter.

 

Thank you, I will take a picture of the diagram when I get home today.

Yes, I am only measuring across. I'll check for low voltage with the inside unit set to on this afternoon as well.

The box out side has a breaker style switch, not a pull style fuse. I'll look into that.

Its really strange to me that the fan is getting power when the contactor doesn't appear to be engaged at all.

 

Your picture is taken from a little too close. The top of of the contactor is normally going toward the compressor. I will call that T1 and T2.

The bottom of the contactor is usually fed from incoming power. These are L1 and L2.

Turn off the breaker.

Disconnect the heavy black and the heavy red wires on T1 and T2 and disconnect the orange wire from Herm. Tape them off individually with electrical tape.

Restart the unit and see if the fan now operates normally and the breaker no longer trips.

If the breaker didn't trip this time, I would turn the power back off and take a look at the compressor terminals. If you are lucky you only need a term lock kit.

It is much more likely that you have a grounded compressor and need a new unit.

 

OK, while I was home for lunch I did a quick check of the outside disconnect box. I turned on the inside breaker and it stayed on. Then I turned on the outside disconnect, the fan started spinning.

I checked the bottom of the disconnect and it had 0v then I checked the top of the disconnect and it had 240v, then after a minute the inside breaker flipped.

The top is in from the house and the bottom is out to the AC. Would I next check one side at a time top to bottom for 120v? Or should I leave it off and just check each side top to bottom for continuity? And does it appear that this is would have a replaceable fuse inside it, or is it just a second breaker? It didn't look like any piece could be pulled out.

 

Ok..... you've confirmed that you have 240vac to the condensor. Turn it off and try the tests that Houston left you.

You are going to need a meter to diagnose this problem.

You more than likely have a shorted compressor or fan motor. Since that contactor leaves one half of the power connected at all times.... a shorted windiig in one of the motors is most likely the problem. Trying to restart the condensor at this time will more than likely increase the damage.

 

Thanks Houston, I was just posting about the disconnect when you posted this. Yes it looks like the bottom of the contactor is coming from the outside disconnect box, and it looks like the top is out to the fan, compressor, capacitor. (but I will double check tonight,) I think its wired correctly from what I have read and seen, which is why I am currious why I would have power there if there is no power at the bottom of the contactor.

There is a red wire from the top of the contactor directly to the capasitor. And since I am getting 120v at the top I am assuming thats whats causing the fan to come on. I cant tell if the compressor is also trying to come on or not.

I have been seeing people talking about backflow power, but am still trying to learn if that is the issue of having power at the top when none is coming in from the bottom.

But there does seem to be an issue with the disconnect as I am getting 240 in from the breaker box but getting 0 on the other side of the disconnect, then the breaker flips after a minute.

 

Thanks PJMAX, I am not sure I am getting 240v to the compressor, I think I may only be getting 120v through the disconnect and one side may be out.

I think I need to go home and check to see if only 1 side of the disconnect is letting power through. I was reading 240v at the top to terminals coming from my inside breaker box, but reading 0v at the bottom 2 terminals.

Could a short in 1 of the motors, cause me to get a 0v reading at the disconnect on the bottom terminals?

 

The 0 volts at the bottom of the contactor isn't the problem. Tripping the breaker is. That is only a 1 pole contactor which means one leg of the 240v power is always connected to the compressor and fan. With the contactor open..... neither the fan or the compressor should run.

You said the fan is running. That's a problem that needs to be found and has nothing to do with the contactor,.

 

Thank you, and I do get what your saying. The fan running is a for sure problem. I will disconnect and run through the steps Houston suggested first.

I am just also thinking that I might not be getting full power to the system because one side of the disconnect that is mounted to the house is not working. As a separate issue. But perhaps its all tied together if there is a short at the compressor or fan.

 

You have confirmed 240v to the input side of the contactor. That is good. That means the proper voltage is being connected to the unit. Now to locate the internal short.

 

I'm sorry if I ever mentioned 240v to the contactor, I have only been getting 120v from the output (top) side of the contactor. the input (bottom) side has only read 0v.

I am getting 240v to input of the disconnect box mounted on the house and 0v on the output of the disconnect.

But perhaps I'm not explaining it correctly or using a wrong term.

I will go home today and do some more poking around before I come back with more questions.

Thanks for your time while I try and diagnose it.

 

PJMax and Houston, thank you for your help so far. PJ once I got home and looked at the system again, what you were saying finally clicked, sorry for the denseness. I only got 1/2 way through the steps Houston suggested.

I unhooked the top red, black and orange wires from the compressor and taped them off. Then turned everything back on, the breaker did NOT flip and the fan did NOT start running. I turned on the inside ac and the contactor clicked down and engaged, and I was getting the 24v to the sides. So the contactor seems to be functioning.

When the cold was being called obviously the compressor did not try to start since it was unplugged, the fan also did not try to start.

Should the fan have started? Or is it correct for it to stay off with those wired disconnected?

I will check the connections on the compressor tomorrow.

 

Yes, the fan should have started.

Do you have a multimeter?

 

yes i do. thats how i have been testing the voltage.

 

Turn off the breaker and measure the resistance between each of the 3 compressor wires to ground.

I always avoid the buzzing continuity setting and choose the Ohm setting.

If you do not see proof of a short on the compressor wires, check the fan motor wires to ground.

 

A fast check for a short to ground is T1 and then T2 to ground.

That unit probably has a crank case heater on the compressor. I have seen this item short out on the 10 to 12 SEER units.

 

Ok, I havent been able to get a clear photo of the wire diagram yet, still working on it.

But I went home at lunch today and go the following results, I hadnt seen your post about the crank case heater yet.

With my multimeter set to 200 Ohm, using the ground wire that is bolted to the metal unit as the ground I got these results:

Compressor wires
Black+Ground = .5
Red+Ground = .3
Orange+Ground = 1.8

Black+Red = .5
Black+Orange = 1.8
Red+Orange = 1.8

Fan Wires
Brown+Ground = 77.5
Purple+Ground = stayed on the 1 on the left of the read out with no activity
Black+Ground = 27.1

Brown+Purple = 76.8
Brown+Black = 51
Black+Purple = 25.8

 

If the compressor and fan wires are 100% disconnected..... you should read NO continuity to ground.

If you have the three compressor wires disconnected and just floating in the air.... your compressor is shorted internally and needs to be replaced.

Based on your low resistance to ground on the red wire.... that is the shorted winding to ground. That explains why you trip the breaker when the contactor closes because it's the red wire that the contactor powers when it's activated.

 

Yes these were all with the wires unplugged and hanging.

 

Yep, it sounds like it's time for a new unit.

I would still put on some safety glasses and look at the compressor terminals.

If you are lucky, you might only have a short in the wire connection to the compressor.

A Term Lok kit is a fraction of the cost of a new unit.

It is unlikely though and you have to stand on your head to check. (Or snap a picture with your phone after removing the compressor terminal cover)

Damaged compressor terminals can blow the refrigerant charge into your face. It never feels very safe checking this area.

 

Thanks for your help everyone. I believe I will call a tech out to check it out further.

It was good to learn a little bit more about the system, as all I had done int he past was replace a capacitor at a previous house we stayed at.

Its been cool in TX so I have not been in a hurry. But the system is 17 years old and the previous home owner obviously did not take care of the system, the inside coils were horrible when I moved in and I spent hours cleaning them.

Thanks again.

 

You're welcome. Sorry we didn't have some better news. Let us know how you make out.

 

It is 70°F and 33%RH outside this evening in the Houston area.

If every day was like this I would be out of a job.

 

Ok, just had a tech out and for sure the compressor is grounded.

Would you mind giving a little feed back on what price range a new system should be. I know it is going to vary greatly by model, brand, and size. But as I have never bought one it would be nice to have some idea what I should be looking at.

The house is about 1600sqft, one story. The current trane is 3ton 12seer.

This first guys quotes with installation ranged from 17000 on the high end to 9000 on the low end for a trane xr16.

I was hoping to find something closer to 4-6k installed, is that possible with a cheaper brand than trane? I was thinking about looking at a Bryant dealer next.

 

You will not get a 4000 dollar system but you should be able to get a system below 9000 dollars if you get a different brand.

I prefer Carrier over Trane and the price might be better than Trane.

Rheem would be a less expensive option.

 

Thanks again for everyones info. I learned a lot with this project.

Ended up getting a Rheem system installed for less than 5000 dollars by a licensed tech that was local to my neighborhood, they did a nice clean install with a smart thermostat.

Its running really well now.

 

Great news. Thanks for letting us know how you made out.