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Old 08-19-2012, 02:15 PM   #1
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How to Know if Transformer of Controller Board is Blown


I've got a Carrier HVAC electric furnace that I seem to have shorted a component in.

I was installing a new thermostat and must have shorted the 24v wires during the install. The new thermostat was working and then when I dis-assembled it to mount it permanently that's when the problem occurred. I've traced the lack of power all the way back to the controller board.

The controller board is a model HK61EA and the transformer is model number AT175A1008. I can replace both but the control board is $250 so I'd rather swap the $30 transformer first. My only question is how do I know which one is faulty?

Incidentally I checked the 5v fuse on the control board and it's NOT blown (replaced it with a few backups too). The LED light on the the control board is also dead. Checked the main power to the unit and it seems to be hot. My guess is that the control board is fried somewhere or the transformer is not powering it.

Any suggestions?

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Old 08-19-2012, 03:16 PM   #2
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How to Know if Transformer of Controller Board is Blown


check power into and out of the transformer using a volt meter (do this only if you know how to and feel safe doing so)

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Old 08-19-2012, 04:16 PM   #3
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How to Know if Transformer of Controller Board is Blown


I believe there are two leads coming out from one side and two leads coming from the other. I have a voltimeter. What is the appropriate way to check the leads for a transformer?

Are each of the leads coming from either side hot/cold?
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Old 08-19-2012, 04:49 PM   #4
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How to Know if Transformer of Controller Board is Blown


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(do this only if you know how to and feel safe doing so)
again, if you don't know how to do this, then DON'T! Call a pro.
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Old 08-19-2012, 07:48 PM   #5
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How to Know if Transformer of Controller Board is Blown


Did that thermostat come with instructions? If it did I'll bet it said "turn off power first"
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Old 08-19-2012, 08:58 PM   #6
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How to Know if Transformer of Controller Board is Blown


Find the 2 transformer leads that supply 24 volts to the board, and see if you read 24 or more volts.
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Old 08-20-2012, 07:21 AM   #7
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How to Know if Transformer of Controller Board is Blown


Quote:
Originally Posted by wilschroter View Post
I've got a Carrier HVAC electric furnace that I seem to have shorted a component in.

I was installing a new thermostat and must have shorted the 24v wires during the install. The new thermostat was working and then when I dis-assembled it to mount it permanently that's when the problem occurred. I've traced the lack of power all the way back to the controller board.

The controller board is a model HK61EA and the transformer is model number AT175A1008. I can replace both but the control board is $250 so I'd rather swap the $30 transformer first. My only question is how do I know which one is faulty?

Incidentally I checked the 5v fuse on the control board and it's NOT blown (replaced it with a few backups too). The LED light on the the control board is also dead. Checked the main power to the unit and it seems to be hot. My guess is that the control board is fried somewhere or the transformer is not powering it.

Any suggestions?
white and black going to transformer 120 volt in....other wires maybe yellow and blue comming out 24volt trace to board 24 volt at board terminals or it could be greater...if you have correct voltage at board.....bad board or fuse...you said you changed fuse..bad board..if no voltage at board bad trans..
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Old 08-20-2012, 10:07 AM   #8
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How to Know if Transformer of Controller Board is Blown


Quote:
Originally Posted by wilschroter View Post
I've got a Carrier HVAC electric furnace that I seem to have shorted a component in.

I was installing a new thermostat and must have shorted the 24v wires during the install. The new thermostat was working and then when I dis-assembled it to mount it permanently that's when the problem occurred. I've traced the lack of power all the way back to the controller board.

The controller board is a model HK61EA and the transformer is model number AT175A1008. I can replace both but the control board is $250 so I'd rather swap the $30 transformer first. My only question is how do I know which one is faulty?

Incidentally I checked the 5v fuse on the control board and it's NOT blown (replaced it with a few backups too). The LED light on the the control board is also dead. Checked the main power to the unit and it seems to be hot. My guess is that the control board is fried somewhere or the transformer is not powering it.

Any suggestions?
Set meter to AC volt scale higher than 24 volt. On probly the two black wires should be 110 or maybe a little higher and on the other 2 lead's on the other side comming out of transformer 24 or maybe a litter higher. If no 24 volt than open transformer Unless you shorted the diode or diode's that supply the DC on the board ?? Than If the fuse is ok probly the diode's are ok?? Just need to troble shoot it. good luck
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Old 10-15-2012, 04:58 PM   #9
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How to Know if Transformer of Controller Board is Blown


Good afternoon,
I have run into the same problem. No power to the thermostat, and I went upstairs to check power. I had no power to transformer. I purchased a new transformer and replaced it. I followed the wiring, and rechecked it. No power. I am kinda frustrated so I thought I would email to see what it could be. I am thinking it's the board.

Ideas?
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Old 10-15-2012, 06:03 PM   #10
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How to Know if Transformer of Controller Board is Blown


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Originally Posted by hypnoron View Post
Good afternoon,
I have run into the same problem. No power to the thermostat, and I went upstairs to check power. I had no power to transformer. I purchased a new transformer and replaced it. I followed the wiring, and rechecked it. No power. I am kinda frustrated so I thought I would email to see what it could be. I am thinking it's the board.

Ideas?
need to check to see if you have 120 volt to furnace junction box...then to door switch..then from there.....could be blown fuse stat at on and off switch...ben sr

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