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Douglas
Douglas, HVAC Technician
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we have a model t9mpv075f12c1 and it is 7yrs old and in the

Resolved Question:

we have a model t9mpv075f12c1 and it is 7yrs old and in the spring we had a new control board put in and since then it has a humming sound coming out of it even in the summer when it is not running.Is this normal.
Submitted: 1 year ago.
Category: HVAC
Expert:  Airheatman replied 1 year ago.
Hello. My name is XXXXX XXXXX I'll do my best to help. Troubleshooting often requires meters and test equipment. Let's get started and see what we can do.
Did they replace the 24 volt transformer also? often a transformer will hum.Sometims you can tighten down the mounting screws to quieten this down
Customer: replied 1 year ago.

we are not sure of what he did, but will look for the invoice.


 

Expert:  Airheatman replied 1 year ago.
Take a look on the blower housing for the transformer. try tightening or loosening the mounting screws and see if the humming quietens. You can also install a piece of gasket material between bracket and metal if this indeed is where noise is coming from. I have to step away but will check back in when I return to see what you found. Transformer will look similar to this and be mounted on blower housing plate.graphic
Customer: replied 1 year ago.

the invoice says only control board changed. also, is any steady humming normal when the furnace is not running. he has gone to check on the transformer. will let you know.

Customer: replied 1 year ago.


the transformer seemed ok..but it is still humming.

Customer: replied 1 year ago.


I have to leave for an hr..send me an email with your answer

Customer: replied 1 year ago.


ok waiting for an answer

Customer: replied 1 year ago.
Relist: Incomplete answer.
did not get an answer on why the furnace is humming when it is not running
Expert:  Douglas replied 1 year ago.
Hi, I'm Douglas and I am here to help you resolve problems with your heating and cooling equipment.

Generally speaking Tim is correct here. The transformer is really the only thing powered when the furnace is in standby mode although there is one relay on the board, it is too small to hum loudly.

The transformer can hum and in certain conditions, the furnace control cabinet can act like a speaker. It may be worth remounting the transformer or trying another one, the noise is the 60 hz buzz that comes from the small magnetic field around the transformers iron core. Actually given the peaks of 60 hz, it will actually hum at 120 hertz (times per second). The actual noise comes from what is called magnetostriction. It's the plates inside the transformer becoming excited.

Improperly wired accessories can also cause a hum but unless we knew they were installed, we couldn't guess at that.

Again remounting the transformer or trying an alternate one may resolve the issue
Douglas, HVAC Technician
Category: HVAC
Satisfied Customers: 3045
Experience: Manufacture Rep for Major Brand, Technical Trainer, NATE
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