Tough transformer problems with carrier heat pump. Please help!

[sylvester36]

I've got a carrier heat pump unit that's about 5 years old. I've self-maintained this unit since it went out of warranty, but this problem has me baffled.

Basically about 2 weeks ago there was a series of storms and as usual we had a lot of intermittent power problems. At one point , someone heard what could be described as a clacking noise inside the air handler and the unit then went dead.

I proceeded to debug and found that the transformer was not registering any low side voltage, but 220 was at the high side. It was strange, because this unit has a 5 amp fuse on the fan control board which appears to be right in line after the transformer (just before the fan relay). This fuse was not and still isn't blown.

So, I ordered two generic type transformers (matching specs) off Ebay. I hooked one up and popped back in the inside disconnect. Immediately I heard a pop and the inline 2 AMP fuse that came with the new transformer had blown Still the 5 amp fuse on the control board in intact. The new transfomer also now appears to be fried as I don't get any low side voltage.

I've since checked and rechecked every wire and connection I could all the way out to the outside unit and even inside to see if I could find any chafing. I'm not sure , but I also checked resistance across the contactor with my meter set at 20 ohms. It did register some resistance. I have had problems with the contactor mechanically in the past and have cleaned/filed the contacts on it. The unit outside turns on if I manually push the contactor in and I believe the compressor and fan run.

What else could be wrong here? Is it possible that the 2 amp fuse is not big enough for this unit? Also, I don't know what the point of the protection fuse is when the transformer blows anyway? I have one more new transformer I ordered as I figured I might need it. Please give me some ideas so I don't have to blow it too. Really can't afford an AC tech right now Thanks much!

[HayZee518]

disconnect the power breaker and take apart the motor contactor. your cleaning of the contacts is ok, but the root of the problem appears to be the operating coil of the contactor. the low voltage coil overheated and melted its internal windings together changing the ohmic resistance of the coil. so when you hitch up the transformer it's seeing a dead short and burning itself out or blowing the secondary fuse.

[sylvester36]

disconnect the power breaker and take apart the motor contactor. your cleaning of the contacts is ok, but the root of the problem appears to be the operating coil of the contactor. the low voltage coil overheated and melted its internal windings together changing the ohmic resistance of the coil. so when you hitch up the transformer it's seeing a dead short and burning itself out or blowing the secondary fuse.

What am I looking for with the contactor and coil? Is there any sure way to test it?

Also, I got to thinking that maybe the fan control board is somehow bad? I was wondering because the fuse and the new transformer blew which were just before the fan control board.

If I just knew how to surely test the contactor/coil and the fan control board I could probably narrow this down. I read somewhere that you can test for continuity to ground from the two fuse terminals on the fan control board to see if it is bad. I took the board off unplugged it and did this, and didn't see any connection to ground. So, if that's a sure test, then my fan control board should be OK ... but I'm not sure.

Also, how/why is the inline protection fuse blowing but not protecting the transformer? Is there any way I can test for a short before I hook up the new transformer? I'm also wondering if I should bypass the 2amp inline fuse that came with the new generic transformer and hook directly to the fused fan control board as the original transformer did.

[HayZee518]

the control transformer has two windings. the high voltage side is marked H1-H2, the low voltage side is marked X1-X2. one side of the control transformer, X2 is grounded to the chassis frame, the X1 or secondary HOT is fused. As far as the contactor is concerned physically take it out and take it apart. if you can't move the crossbar, the operating coil is shot. don't complicate trouble shooting. once you've exhausted all mechanical problems THEN go into the nitty gritty. You got yahoo messenger? add me and we'll go through this. tjmierzwa35

[sylvester36]

the control transformer has two windings. the high voltage side is marked H1-H2, the low voltage side is marked X1-X2. one side of the control transformer, X2 is grounded to the chassis frame, the X1 or secondary HOT is fused. As far as the contactor is concerned physically take it out and take it apart. if you can't move the crossbar, the operating coil is shot. don't complicate trouble shooting. once you've exhausted all mechanical problems THEN go into the nitty gritty. You got yahoo messenger? add me and we'll go through this. tjmierzwa35

I wonder if I hooked this thing up wrong. Didn't realize the trans was chassis grounded. To test, I just had it sorta sitting in the unit and it may have been on top of a wire or had a bad ground.

The other thing is I didn't see any polarity on the low side so I just hooked up the two wires. The old/new colors don't match. New one has red wire (fused) and another color. My carrier wires are red/brown. I did match red to red, but not sure if this is right.

Going to take off the contactor now and see if I can spot this mechanical failure you are describing. Added you on Yahoo. Thanks!

[sylvester36]

Finally got it back running again, but not quite.

At first everything was running, but the condenser and freon lines were getting HOT instead of cold. I'm assuming this had something to do with the reversing valve. So, I took everything back off again and made sure the connection was OK with the reversing solenoid. Started it back up and at one point I swear I saw sparks and heard a few pops from the fan relay on the fan control board Then, no action and the transformer blew again. High side open as before. I'm assuming this is a fan control board problem, but I'm still not sure about the hot condenser.

[HayZee518]

we got to go about this one step at a time. the arcing you saw could be the contacts opening under load for the fan motor as its supposed to do. if the fan blower is obstructed by some means, hitting the shroud, unlubed bearings, the motor amperage will go up. I wish you had a schematic to send. is the reversing valve 24 volts or 240 volts? in a heat pump you have backup heat usually electric that operate off a heat sequencer. the sequencer also uses 24 volts for control. there are extra contacts on the sequencer that also run the same blower as used for cooling.

[sylvester36]

This one seems to be "fixed" on the inside. Well, I got the fan to go on and off without blowing the trans. I did (finally) blow the 5amp fuse. I replaced it with a 10amp and checked the wiring outside. It seemed to work after that. I'm doing another thread for this reversing valve problem now I seem to be having.