Condensing unit fan motor question - InspectionNews

Rick Hurst · #1 (**permalink**) 02-02-2009, 07:17 AM

Can any of you HVAC guru's advise me on why a condensing unit fan motor would run continuously even though the thermostats are in the off position?

If the breaker at the panel box is switched on, the fan on the condensing unit runs but not high speed, but more in a slower speed.

Rick

Jerry Peck · #2 (**permalink**) 02-02-2009, 07:23 AM

Not an HVAC guy, but ... something wired wrong would be my guess. Either that or something going bad and allowing a tremendous amount of bleed through current.

The contactor should keep that off if the contactor is wired correctly and is not pulled in by the thermostat.

Richard Stanley · #3 (**permalink**) 02-02-2009, 08:19 AM

May be bad limit switch.

A.D. Miller · #4 (**permalink**) 02-02-2009, 08:20 AM

Quote:

Originally Posted by Rick Hurst

Can any of you HVAC guru's advise me on why a condensing unit fan motor would run continuously even though the thermostats are in the off position?

If the breaker at the panel box is switched on, the fan on the condensing unit runs but not high speed, but more in a slower speed.

Rick

Rick: One possibility: thermostat is bad or battery is bad AND one side of the bridged breaker is bad. Or, a multi-speed condenser that is malfunctioning?

Dave Hill · #5 (**permalink**) 02-02-2009, 09:28 AM

For what it's worth, I've seen some units that run the fan to circulate air, but only for about 10 minutes and then it shuts off. It did this even when the thermostat was set to off (not heat or cool mode).

Of course this was not continuous like you saw.
BTW, I'm definately not a HVAC guru.

Jerry Peck · #6 (**permalink**) 02-02-2009, 09:38 AM

Dave,

That is for the AHU, one of the ways they achieve the higher SEER ratings.

He is talking about the condenser unit outside.

Paul Kondzich · #7 (**permalink**) 02-02-2009, 12:23 PM

Does it appear that the fan has been changed at some time? Maybe some genius wired to a continuouus power source, like maybe the wrong side of the contactor.

Jim Luttrall · #8 (**permalink**) 02-02-2009, 02:00 PM

Bad contactor... but the compressor is typically on the same contactor so I would think the compressor would be trying to run. With the fan motor running at less than full speed it may be one of the older units that just breaks one leg of the 240v and the motor windings have gone to ground part way through the winding. It is just running on 120v until the breaker is shut off. Then when the breaker and contactor are on, the motor runs at nearly full speed.
IF it is a newer unit with solid state multi-spead fan, then all bets are off. Look at replacing the circuit board.
If it is a heat pump, make sure you allow time to cycle through defrost delays.

Darrel Hood · #9 (**permalink**) 02-03-2009, 04:13 AM

I saw this recently on new construction. The thermostat connection was incorrect.

Also, I have heard, though not from a credible source, that some High Velocity systems run continuously.

Darrel Hood
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