Low transformer voltage through control board

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Old 10-24-19, 11:56 AM
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Low transformer voltage through control board

I am somewhat baffled by this issue and am hoping someone can point me in the right direction.

My HVAC stopped working a few days ago and I diagnosed it as a control board failure, but I still have the same symptoms with the new board. When I remove the transformer from the unit and wire it directly to a 120v wall outlet, I get 28v output. When the transformer is powered through the control board Initially get 20v output, but it gradually decreases to 1-2v and holds steady there. If I measure the voltage supplied to the transformer from the board I get 120v if the transformer is disconnected, but only 5-10 with it plugged in.

I thought there may be a short, so I have disconnected all wires from the control board and only input power and transformer are remaining. Same result. Any ideas?
 
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Old 10-24-19, 12:07 PM
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It's not going to be a short. When there is a short things burn, and spark and blow up.
It's more like a poor connection.

If the 120v coming from the board to the transformer is failing.... it's likely the 120v to the board is failing. There are usually several neutral connections all tied together on the board. There are also several hot connections. Rarely do they go bad on the board.

Check the 120v supply to the board.
Post the part number of the board.
 
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Old 10-24-19, 12:55 PM
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As soon as I submitted the original lost I had the same thought on the input power. It turns out that there was a short in the junction box inside the unit and all of the wires and nuts were burned up. The connection was still enough to read 120v at the board, but as soon as the transformer was connected it pulled too much load for the burned up wires to handle. I will re-wire the box and hopefully will be good to go.

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Old 10-24-19, 01:51 PM
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Not a short...... poor connections.
They were not attached solidly, got loose or corroded, created heat and burned open.
 
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