Intermittent Air Handler Fan
#1
06-18-15, 06:46 PM
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Intermittent Air Handler Fan
Equipment: Amana RHE36A2A heat pump and Amana BBC36A2A Air Handler, installed May 2002
Symptoms:
AC works some of the time then air handler fan stops working. To protect compressor I then turn off AC. I try turning it on again every few hours until it works.
About 16-24 hours later turning AC on again may cause fan to restart and AC works fine again for 1/2 day to 8 days.
Sometimes the fan tries to restart but cant get going. Speeds up then turns off, repeats this cycle 4 or 5 times, then stops.
Problem is severe now (Arizona summer). Problem started at tail end of winter season when heat pump was in heating mode.
Diagnosis attempts:
Thermostat was changed but made no difference.
When not working manually switching on fan at thermostat causes relay to click on air handler interface board, but fan stays off.
24v ac measured between R & C on control board. 0.36v between R & G when switch in fan on mode. Both seem correct.
Air handler control board has an LED that flashes correctly to indicate board is working.
Disconnecting thermistor wires causes control board to correctly flash at a different rate.
Measured resistance of thermistor, seems to be correct for the ambient temperature.
Interface board also has a LED to flash the CFM rate. When AC not working LED can be seen flickering in dim light.
Suspected interface board so disconnected then reconnected cables to check for bad connections. It may have helped a little for a while, but maybe wishful thinking.
Fan runs freely, no unusual noises, no jerkiness when fan switch on attempted.
Called out AC repair technician but unit decided to work when he came!, and repeated on/off attempts did not reproduce the problem. So no fault detection possible. Technician suspects interface board or bad motor.
Other info:
Compressor fan capacitor replaced last year to fix compressor fan problem. Compressor works fine now.
So to avoid another wasted service charge does anyone have any further ideas? Many thanks in advance for your help.
Brian
Symptoms:
AC works some of the time then air handler fan stops working. To protect compressor I then turn off AC. I try turning it on again every few hours until it works.
About 16-24 hours later turning AC on again may cause fan to restart and AC works fine again for 1/2 day to 8 days.
Sometimes the fan tries to restart but cant get going. Speeds up then turns off, repeats this cycle 4 or 5 times, then stops.
Problem is severe now (Arizona summer). Problem started at tail end of winter season when heat pump was in heating mode.
Diagnosis attempts:
Thermostat was changed but made no difference.
When not working manually switching on fan at thermostat causes relay to click on air handler interface board, but fan stays off.
24v ac measured between R & C on control board. 0.36v between R & G when switch in fan on mode. Both seem correct.
Air handler control board has an LED that flashes correctly to indicate board is working.
Disconnecting thermistor wires causes control board to correctly flash at a different rate.
Measured resistance of thermistor, seems to be correct for the ambient temperature.
Interface board also has a LED to flash the CFM rate. When AC not working LED can be seen flickering in dim light.
Suspected interface board so disconnected then reconnected cables to check for bad connections. It may have helped a little for a while, but maybe wishful thinking.
Fan runs freely, no unusual noises, no jerkiness when fan switch on attempted.
Called out AC repair technician but unit decided to work when he came!, and repeated on/off attempts did not reproduce the problem. So no fault detection possible. Technician suspects interface board or bad motor.
Other info:
Compressor fan capacitor replaced last year to fix compressor fan problem. Compressor works fine now.
So to avoid another wasted service charge does anyone have any further ideas? Many thanks in advance for your help.
Brian
#2
06-19-15, 03:40 AM
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Check all wiring from the fan to the point where those wires terminate .
You could check the amperage and voltage of the indoor fan motor . A cheap clamp on meter from Harbor Freight should work . Probably have 3 wires to the fan . Check the common , if not sure , check all 3 and compare those numbers with the name plate data on the motor .
If you do not have voltage to the fan , then I suspect the fan relay . Do not know if it is on the control board or a separate component ?
Capacitors for the indoor fan , do go out from time to time . They are not too expensive . You may wish to buy one and try changing it out . If it does not fix it , keep the old one as a spare .
I think you said the fan spun freely ? So bearings are probably OK .
At this point I would start thinking about replacing the motor . A new motor may or may not use the same capacitor as the old motor . Buy a new capacitor specific to the new motor , if needed . Id they use the same value of capacitor , use the new one you just purchased ( if you left it connected & in use only breifly ) .
God bless
Wyr
You could check the amperage and voltage of the indoor fan motor . A cheap clamp on meter from Harbor Freight should work . Probably have 3 wires to the fan . Check the common , if not sure , check all 3 and compare those numbers with the name plate data on the motor .
If you do not have voltage to the fan , then I suspect the fan relay . Do not know if it is on the control board or a separate component ?
Capacitors for the indoor fan , do go out from time to time . They are not too expensive . You may wish to buy one and try changing it out . If it does not fix it , keep the old one as a spare .
I think you said the fan spun freely ? So bearings are probably OK .
At this point I would start thinking about replacing the motor . A new motor may or may not use the same capacitor as the old motor . Buy a new capacitor specific to the new motor , if needed . Id they use the same value of capacitor , use the new one you just purchased ( if you left it connected & in use only breifly ) .
God bless
Wyr
#3
06-20-15, 01:41 PM
Join Date: Jun 2015
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Intermittent Air Handler Fan
Thanks for fast response.
The circuit diagram doesn't show any capacitors around the motor, perhaps they are hidden inside. (page 7 of http://johnstonesupply9.com/TechDocs...ECH%20INFO.pdf
)
When the technician was here he tried a clip on meter which didn't indicate a problem since the unit was working properly at the time. However your suggestion to get my own meter is a good one. When the unit stops working again then I can check it myself.
The relay is on the interface board, which is separate from the control board. I am hoping that is the problem and not the motor. The fan turns freely, and when working the motor is noise free.
Thanks, Brian
The circuit diagram doesn't show any capacitors around the motor, perhaps they are hidden inside. (page 7 of http://johnstonesupply9.com/TechDocs...ECH%20INFO.pdf
)
When the technician was here he tried a clip on meter which didn't indicate a problem since the unit was working properly at the time. However your suggestion to get my own meter is a good one. When the unit stops working again then I can check it myself.
The relay is on the interface board, which is separate from the control board. I am hoping that is the problem and not the motor. The fan turns freely, and when working the motor is noise free.
Thanks, Brian
#4
06-20-15, 02:37 PM
Member
Brian, I would suggest that you take a voltmeter and make voltage measurements on the motor wires, particularly from RD1 (Fan) to BK1 (Fan Com) while the motor is working. Then, when it stops working, see if you have the same voltages present. If you do, then it's likely the motor. However, if the voltage is not present, then it's likely a problem with the control board.
