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Old 06-22-2009, 09:07 AM   #1
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blower motor cycles on and off very often only in A/C mode


The blower motor cycles on and off very often, but only in cooling mode.

In cooling mode only (when thermostat is set for cooling and set temp is lower than room temp). The outside condensor will run continuely, but the blower motor (fan) will cycle on and off every often (on a few min and off a few min), this is happening regardless of the fan setting of on or auto.

At first I thought there is some kind of thermo cutoff in the blower due to over heating, but if I turn off ac or set the temp above room temp in cooling mode and switch fan to on mode from auto mode, the blower will run fine for several hours straight without any problem.

Thanks in advance for any help.


Last edited by carrara; 06-26-2009 at 07:17 PM.
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Old 06-26-2009, 07:16 PM   #2
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blower motor cycles on and off very often only in A/C mode


Here is a picture of the white rodgers controler, please help if you can.

<img src="http://i221.photobucket.com/albums/d...a/41f50927.jpg">
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blower motor cycles on and off very often only in A/C mode-dscn1637.jpg  

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Old 06-26-2009, 09:04 PM   #3
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blower motor cycles on and off very often only in A/C mode


Is the t-stat at desired setpoint when indoor blower shuts down?
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Old 06-26-2009, 09:31 PM   #4
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blower motor cycles on and off very often only in A/C mode


It could be eather the WR board or the blower mtr cooling speed. When you put the fan switch to on and run only the fan it is operating the motor in the heat speed setting.
Try and switch the heating and cooling speed wires on the WR board and run it in the fan on setting again this will run the cooling speed. If it then runs without fault it must be the board.
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Old 06-26-2009, 10:43 PM   #5
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blower motor cycles on and off very often only in A/C mode


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Is the t-stat at desired setpoint when indoor blower shuts down?
No. the indoor blower will run for a few min and off a few min until the desired temp is reached while the outdoor unit is running non stop. (during very hot temp outside, the indoor may never reach the set temp)
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Old 06-26-2009, 10:47 PM   #6
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blower motor cycles on and off very often only in A/C mode


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Originally Posted by JohnH1 View Post
It could be eather the WR board or the blower mtr cooling speed. When you put the fan switch to on and run only the fan it is operating the motor in the heat speed setting.
Try and switch the heating and cooling speed wires on the WR board and run it in the fan on setting again this will run the cooling speed. If it then runs without fault it must be the board.
Can you tell me which two wires to switch to test the board? I am kind of guessing the ones on the right side of the board? Just want to be sure? What about the dip switch? where can I find a wiring diagram? (I was not able to find anything on white rodgers site) Thanks a lot.
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Old 06-27-2009, 02:21 PM   #7
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blower motor cycles on and off very often only in A/C mode


You may have a contactor that is putting an excessive draw on the low voltage which is causing the blower relay to drop out from a lack of voltage. Could also be a voltage drop from the thermostat.
If you have a meter check your board, r to c, y to c and g to c with the ac running. Then turn ac off and turn the fan on and check all again. Let us know what you find.
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Old 06-27-2009, 08:48 PM   #8
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blower motor cycles on and off very often only in A/C mode


I would say to check the cooling speed terminal at the board & see if you are loosing voltage (110-120) when the fan stops.. If not I would say something is getting hot on the board & dropping the voltage to the relay that feeds the fan
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Old 06-28-2009, 09:51 PM   #9
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blower motor cycles on and off very often only in A/C mode


Quote:
Originally Posted by carrara View Post
Can you tell me which two wires to switch to test the board? I am kind of guessing the ones on the right side of the board? Just want to be sure? What about the dip switch? where can I find a wiring diagram? (I was not able to find anything on white rodgers site) Thanks a lot.
Look at were the wires are plugged in at on the right side of the board the terminals are usually marked heat and cool. they are probly the black for cool and the blue for heat.

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