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Old 11-20-2011, 10:43 AM   #1
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Rapid Blower Motor Cycling


Hello,

I'm new here, but I've been trying to find posts on a similar issue and I have not found any. Here's the scoop, both on heat and A/C settings my blower motor with cycle rapidly when it should just stay off.

The thermostat is not commanding the blower motor to turn on but it rapidly fires on (for less than a second usually) and then off for another second or so. There are long periods of silence (thankfully), but this problem has been persistent since I bought this place last year and ill timed fits sometimes interrupt my sleep.

I have an electric heat pump system (circa 1990) and have even switched out the old mercury switch thermostat hoping that maybe it was a problem with the internal wiring there. Now I'm stumped. Any ideas of what to check next?

My guess is there must be a bum sensor or relay inside my controller board. As someone who's a mechanical and controls engineer, I'm hoping this is something I can fix on my own.

Thanks,

Jeremy
Dayton, OH

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Old 11-20-2011, 11:09 AM   #2
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Rapid Blower Motor Cycling


pull the stat off the subbase jump R to G for fan only yes it comes on does it stay off the board is signaled from the stat might be a feed back bouncing the fan relay on the air handler.do you have a transformer in the air handler and the condenser need to remove the Rh-Rc jumper on the subbase...if you only have a TR in the air handler leave the jumper so it powers the heat side of the pump.maybe even go down to the board and do the same jump R/RED to GREEN/G in the free world it's typical wiring.if the G wire and the R wire were rubbing together from the stat drop into the air handler would be a constant FAN unless mouse(s) are walking by... that random fan in both seasons is the flag you'll find it..remove the board check the backing nothing touching or burnt?,,get back latter

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Old 11-20-2011, 11:13 AM   #3
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Rapid Blower Motor Cycling


Ther may be fan and limit control on your furance that tells the fan to come on at a certian temperature. It also tells the burners to turn off if the heat exchanger gets to hot. What is the make of you furnace, does this occur in both cooling and heating season?
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Old 11-20-2011, 01:12 PM   #4
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Rapid Blower Motor Cycling


The problem occurs in both heating and cooling sessions. Its been silent since it kept me awake while I tried to sleep last night.

The Heatpump/Fan unit is an American Standard : Trane TWV724B140A0.
Air conditioner is an outdoor unit is a Trane XE1000.
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Old 11-20-2011, 01:14 PM   #5
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Rapid Blower Motor Cycling


Quote:
Originally Posted by biggles View Post
pull the stat off the subbase jump R to G for fan only yes it comes on does it stay off the board is signaled from the stat might be a feed back bouncing the fan relay on the air handler.do you have a transformer in the air handler and the condenser need to remove the Rh-Rc jumper on the subbase...if you only have a TR in the air handler leave the jumper so it powers the heat side of the pump.maybe even go down to the board and do the same jump R/RED to GREEN/G in the free world it's typical wiring.if the G wire and the R wire were rubbing together from the stat drop into the air handler would be a constant FAN unless mouse(s) are walking by... that random fan in both seasons is the flag you'll find it..remove the board check the backing nothing touching or burnt?,,get back latter
The problem even occurs if there are no connections on the thermostat. The only way to control the problem is to jump the connection to turn the fan always on. Thanks though
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Old 11-20-2011, 01:37 PM   #6
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Rapid Blower Motor Cycling


Quote:
Originally Posted by JeremyUSAF View Post
The problem occurs in both heating and cooling sessions. Its been silent since it kept me awake while I tried to sleep last night.

The Heatpump/Fan unit is an American Standard : Trane TWV724B140A0.
Air conditioner is an outdoor unit is a Trane XE1000.

You do not have a heat pump unless the outside unit is the heat pump. Never is the indoor blower in the furnace or electric air handler considered the heat pump.
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Old 11-20-2011, 03:36 PM   #7
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Rapid Blower Motor Cycling


Quote:
Originally Posted by biggles View Post
pull the stat off the subbase jump R to G for fan only yes it comes on does it stay off the board is signaled from the stat might be a feed back bouncing the fan relay on the air handler.do you have a transformer in the air handler and the condenser need to remove the Rh-Rc jumper on the subbase...if you only have a TR in the air handler leave the jumper so it powers the heat side of the pump.maybe even go down to the board and do the same jump R/RED to GREEN/G in the free world it's typical wiring.if the G wire and the R wire were rubbing together from the stat drop into the air handler would be a constant FAN unless mouse(s) are walking by... that random fan in both seasons is the flag you'll find it..remove the board check the backing nothing touching or burnt?,,get back latter
There's nothing obviously shorting and nothing burnt out behind the control panel.
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Old 11-20-2011, 04:22 PM   #8
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Rapid Blower Motor Cycling


thats something still happens with no stat up on the subbase....and or wires unscrewed...how about trying disconeecting the stat into the air handler at the control board....if it still runs the board is closing the fan relay from some kind of random signal....if it doesn't cycle with the stat wires disconnected down on the board the bell wiring run from there up to the stat is causing it G and R are touching somewhere..if that board is standing alone with no stat wiring connected the board has to be replaced....what about the 2nd TR in the condensing unit it being a HP?there or not

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hvac control board, hvac duct fan, hvac repair, short cycling


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