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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Intermittent fan cutting on and off in the cold mode, but

Customer Question

Intermittent fan cutting on and off in the cold mode, but only after hours of operation
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: 1 day
JA: Do you plan on doing the work yourself?
Customer: Yes
JA: Anything else we should know to help you best?
Customer: That is all
Submitted: 9 months ago.
Category: HVAC
Expert:  Phil replied 9 months ago.

Hello, tell me please which fan is cutting on and off in cold mode please... there are two possibilities, the fan on top of the outside unit, and the blower inside the air handler that moves the cool air throughout the home.

Tell me please how frequently it cuts on and off... every 5 seconds or every 5 minutes for instance.

We can go from there

Customer: replied 9 months ago.
It's the fan inside the attic that moves the air throughout the home. It also only starts when the temperature is selected to be 70degrees F or below. And it cuts on and off within seconds.
Expert:  Phil replied 9 months ago.

Thanks, ***** ***** the brand and model number of the furnace or air handler that the fan is in.... I have no idea what you have so far... is it that? or a whole house ventilation fan set in a gable or on the roof... there are a few dozen options, each with its own set of probable causes.

Customer: replied 8 months ago.
Ruud silhouette 2, and the fan cuts on and off nonstop when it's cooling the house.
Expert:  Phil replied 8 months ago.

Thanks, ***** ***** are in the 90% range that the furnaces main mother board, printed circuit card, is failing.

If you have or wish to buy a clamp around amp meter you can check the current flow to the motor to see if it is running within its name plate amperage or not,

You can also do a heat stress test on the printed circuit board (mounted on the main blower)... use a hair drier to slowly and evenly warm the card up to 120F then start the furnace again. If you notice any changes for the better or worse you have proven the printed circuit board is bad.

We can go from there.