Transformer keeps blowing

Myst420

Hey guys,

Sorry in advance for the long post, but I don't want to miss anything that may be important.

First off, I am no expert when it comes to hvac, or home electrical systems, but I'm not afraid to get my hands dirty

I have a Payne (made by carrier) 3.5 ton system that is only 1.5 years old.

Last week, one of the 120v leads coming into my house from the electric co went bad, and they had to replace it. When I noticed it was bad, the hvac system was only receiving 120v and was trying to come on. I could hear the outside unit "clicking" continuously.

The next day after the electric co had "patched" their lead until they were able to burry new ones, I noticed the compressor wasn't coming on. I replaced the capacitor (matched all specs (45/5uf 370v)) and the outside unit started up like it was supposed to. It ran for about 1 minute, and then the whole system shut down.

I traced the issue back to the transformer fuse (3a) and replaced that, the system started up again and died after another minute. This time the transformer blew but the fuse didn't. I tested the transformer and had no continuity on the load side.

Today I replaced the transformer with a multi-tap one, using orange and white on the primary side for 230v (what the original one used). When I turned the power on to the handler, it started to come on, and then the transformer blew again (I actually saw it flash). Does the polarity on the load side matter? There is a yellow and blue on the new transformer, and my handler has red and brown, with a ground tapped into the brown.

I'm going to pick up another transformer tomorrow. Should I attempt to wire it only on the primary side and see if it blows? I'm trying to avoid having to call a hvac repair man (I have a 5 month old and really can't afford to at the moment) so I would love to be able to fix this myself.

Any help you guys can give me would be greatly appreciated!

Thanks in Advance,
Mike

PS. I did check all the wiring I could see outside, and everything appears to be fine.

turnermech

Did you replace the fuse or take it out of the circuit? If i rember correctly payne should have a circuit board with fuse on the board. If you replaced the fuse with a 3 and make sure it is a 3 the fuse should blow before the trasformer does iif the problem is in the low voltage side (called the secondary). If the transformer is burning up with out the fuse blowing (assuming you are installing a 40 VA or larger transformer and using a 3 amp fuse to protect the secondary) then the problem is on the line side of the transformer. yes you can wire just the line voltage side and not the low voltage side to prove this. First I would check the incomming power. Check for 240 volts between L1 and L2 and 120 volts betweeen L1 and L2 each to ground. Yellow and blue of the secondary I don't think matter but I connect Yellow to red and blue to brown. Also try to unground the brown wire of the secondary. this ground sometime has cause me problems in the past and it is not needed. Someone may correct me.

Check the control board for the fan/electric heater payne/bryant/carrier air handlers had some issues with this board and the replacement board is completly different and comes in a kit. you may notice this board is burnt or smells burnt. this kit is kind of expensive and most homeowner won't be able to install it.

turnermech

Another thought this is most likely 240 v not 230 v. the line voltage wiring for 240 volt multi tap transformer is IIRC red and white to line. Make sure you tape off un used wires (black and orange) if the un used wires touch any thing in the cabinet they will short out. This taping of the un used wires could also be your problem if you are not doing it.

Missouri Bound

By load side you mean what? The low voltage side? If it blew, then you have a shorted component. Primary side wiring will not blow the load side. Follow your wiring diagram, not just the color of the wires. Does the transformer feed a control board....if so the board is probably fried. Some troubleshooting is needed before you blow another transformer.

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Myst420

turnermech,,

Thanks for the quick reply. I did tape off the extra wires, and according to the diagram on the multitap I have, orange is infact the 240v (it has 120, 208 and 240 [the original stated it was 230 rather than 240]). I did replace the fuse with another. I figured bypassing it would be a dumb move and start me off going in the wrong direction. I did check the voltage on the primary side, and they were exactly as you described. The way you suggested to wire the secondary side is actually how I had it, only I did have the ground connected. I will buy myself a couple more transformers tomorrow (they are only $10 a piece from a local parts house willing to sell to me) and start with leaving the secondary side disconnected.

Mike

Myst420

Yes, by load side I was referring to the low voltage (secondary) side. What confused me is that the fuse did not blow on the low voltage side. I'm at my in-laws now (can't sleep in 87 degree house with the baby) so I will have to wait until after work tomorrow to check the control board. As far as the wiring diagram, I have been trying to do so. I know the primary side was connected properly (Common to white and the other to orange). The secondary side I wasn't too sure of, blue is labeled 24v and yellow is labeled VAC, but I talked to a few guys at the parts house as well as a hvac repairman and was told the secondary side really didn't matter.

Mike

scottmcd9999

Yes, the steps should be:

1) Install the transformer with LINE power ONLY (don't connect the secondary). Turn power on to the furnace, check to see if you have 24v. If you do, then the problem isn't on the LINE side of the tformer.

2) Now turn off power, turn the tstat OFF, and connect ONE SIDE of the LOAD side. If this is a grounded secondary (which many are), then hook up the COMMON side. Turn power back on, and briefly touch the remaing LOAD connection to it's mate. If you see a hard, sharp spark, then you've got a short somewhere and you'll have to remove components one by one to determine which component is giving you troubles. In most cases, that short would be the board itself (assuming you have a circuit board), but it could be due to a chafed/broken wire.

biggles

yellow off the secondary side to the red wire for hot 24Vs,you should of shut the condenser off after loosing that leg,condenser was trying to start on a sigle leg with the stat calling.disconnect the 24Vs wires out into the condenser...during re install of next TR...get one with a secondary CB on it.

Myst420

Thanks for the replies everyone.

I picked up a couple more TRs and will start again once I get home from work. I will check the circuit board first to see if I can notice any obvious shorts on it. Then I will start with leaving the secondary side off completely. The secondary side has a fuse on the side that is grounded...would it be beneficial to me to put a fuse on the other side of the secondary as well?

I did check all the wiring outside and everywhere I could see, and nothing appears to be damaged. I'm really leaning towards this being something other than a chafed wire due to the fact that I didn't have any issues until I lost a main lead from the electric co. btw, once I realized what was going on I did shut the a/c down, and then turn off all the breakers.

I will let you guys know what I find later tonight. If anyone thinks of anything else to check, I'm all ears!

Thanks again,
Mike

scottmcd9999

Put me down for $50 on a fried circuit board.

Myst420

OK guys, heres an update:

I did exactly as Scott suggested, which is how I had the previous transformer connected (minus the ground wire) and everything appears to be working now. I attempted to locate a circuit board in the handler, but didn't see one, so I'm assuming this unit doesn't have one? :confused:

As I type, its been running for about 20 minutes without any issues *knock on wood*. Could the ground wire have been the problem with the previous TR (not the original)?

I just want to say a HUGE THANK YOU to everyone. I've actually learned a lot about HVAC systems in the past few days. I was able to fix my system for a total of $45 and didn't have to call anyone out!


Thanks again,
Mike

turnermech

Should not blow the transformer due to the grounded common wire in the 24v circuit. But that being said I have removed a few ground common leads on old york heat pumps for issues just like you are having. A few are still running today. I can tell you new Payne/bryant/carrier units don't have the secondary grounded as yours does. I installed one bryant and one payne this week alone.

Myst420

I didn't think the ground would short it out either, but that is the only thing I did differently between the 2 transformers.....unless I just happened to get a defective one the first time. Not having the ground wire must be a fairly recent change....the unit I have is less than 2 years old. But either way, I'm happy that everything is working as it should be. Its been running for a couple hours, and the temp has dropped about 5 degrees....only 4 more to go!

turnermech

I have been installing payne and bryant for a long time (on and off for 15years and almost exclusively for 4 or 5). I don't recall them ever using grounded secondary. It is possible I have been not notice them. or it is unique to your model and I might not sell your model. I have seen quite a few york units with them.

turnermech

thought about it some more. I would be willing to bet you have the payne air handler with the X13 motor. I say this because you stated it is around 2 years old and you did not see any fan board. This is a unit I choose not to sell. After selling one I noticed the x13 motor with no relays or boards I inquired about the replacement cost and avaliblity. The price was just a few dollars less than the whole unit. Supply house did not have one in stock. I did not sell any more of the payne with X13 motor.

If the unit is 2 years old and I am correct that is has the X13 you should have it looked at by a HVAC company and most likely it is your problem. It is really the only thing electrical in the air handler. The parts are under warranty. If your temp repair lasts and then fails after warranty this motor cost alot.