About 2 months ago we turned our AC on for the first time this year. We noticed that after about 15-30 minutes, the furnace/central air unit makes a very loud, low pitched humming noise that does not stop until we turn off the AC. This doesn't happen when we have the Heat on, and it didn't happen when we had the AC on last year.

We also don't think Cool air is coming through once this noise begins.

Any suggestions or thoughts?

Thanks,
Michael

It may be an issue with your blower motor on the furnace, may run fine for heating because it will run in low speed but once you kick the A/C on the blower runs in high. I'd check there first.

Thanks for the quick response.

How do I check this - and is it a quick and easy 'fix' or does this generally signal a problem? Should we not run the AC until we have identified the loud noise (for fear of causing more damage), or do you think the loud noise usually means something is wrong?

Thx!

Quote:

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Originally Posted by hvacservicetech_07

It may be an issue with your blower motor on the furnace, may run fine for heating because it will run in low speed but once you kick the A/C on the blower runs in high. I'd check there first.

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I wouldn't advise running it very much without someone looking at it. It sounds to me like it may be the motor bearings, if so you will need to replace the blower motor.