Central A/C fan running backwards?

September 8, 2005 4:51 PM

A/CFilter: Central A/C unit is 7 years old and ran pretty well until this year. Now it barely cools and has to run all day to do it. Have done all the homeowner checks (cleaned unit, checked filter and vents, sealed cracks and ductwork, etc.) A technician charged us $140 (having "cleaned" the unit and checked the coolant) to hold his cigarette up to the running unit and, using the smoke as his diagnostic tool, proclaimed that the fan was running...backwards. He insisted that this can happen with some units after a power surge. Did we just have sex with our clothes on? Or is he for real? Can a fan spontaneously run backwards?

A different tech is coming Monday, and he confirmed that a central air fan can suddenly run backwards if there's an electrical problem...but maybe they belong to the same secret HVAC order.

posted by TN_Tanuki to Home & Garden (3 answers total)

Best answer: I have never heard of this, and I have some professional experience here, but not on the repair side, only engineering an installation. You could check the air flow yourself. Does air flow out of the vents normally? If yes, the fan is running normally. Are they talking about the fan on the condenser outside? If so, the air should be going out of the top of the unit, but even if it were flowing the other way it really shouldn't make much difference.

It sounds more to me like a loss of refrigerant or dirt on the coils. The more sudden the problem the more likely it is a refrigerant issue. Another possible, though unlikely, issue is some sort of blockage in the ducts. You should notice this as reduced output from the vents. If there is blockage of the condenser outside, or the fins have been damage it will also dramatically affect the cooling.
posted by caddis at 5:22 PM on September 8, 2005

Is this an actual air conditioner, or a heat pump?
posted by Thorzdad at 6:04 PM on September 8, 2005

Response by poster: Thorzdad: No, not a heat pump. Just a 2-ton A/C.
posted by TN_Tanuki at 7:35 PM on September 8, 2005