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Old 06-08-2009, 07:31 PM   #1
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How to Troubleshoot A/C Blower motor


I have an older A/C unit that will not blow air. The compressor turns on and the copper tubes gets cold....but the fan/blower does not turn on and does not blow air, it only lurches and tries to get going occassionally until the compressor shuts down. I've set the thermostate fan control from auto to run and I can actually hear a lurching/cluncking sound through the vent system as the blower/motor tries to kick on. I've replaced the run capacitor (10 microfarad/440volt)...but still the same problem. What should I do? Help...it is over 90 degress!!

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Old 06-08-2009, 07:40 PM   #2
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How to Troubleshoot A/C Blower motor


The voltage across closed contactor contacts should be less than 30 mV if they're good, over 100 mV if they're bad.

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Old 06-08-2009, 07:56 PM   #3
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How to Troubleshoot A/C Blower motor


does the squirrel cage spin freely...change the speed wire you should be hooked up right now for hi speed see if you have a medium for now to change to it would be the wires right off the motor might be taped away.if you have heat and the heat runs with the fan(LO)then it is that speed winding(HI) is shot.it is an easy change out and probably match it on the www.grainger.com site.if you see other color wires around the motor maybe HI MED pull/wirenut the HI wire and install the other in its place.
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Old 06-08-2009, 09:43 PM   #4
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How to Troubleshoot A/C Blower motor


Thanks for your reply and suggestions.....the motor has four colored wires (orange, black, & white side by side in one row....then red & blue at a different location on the board) Plus two additional brown wires to the capacitor.
I switched orange and black...and same response...the motor kicks in like a solenoid on a car....but the motor does not take off. The squirrel cage starts up enough to move a little air....but does not get up to speed. I then switched the red & blue wires...same response.
I thought about checking the motor (I have a small little voltage meter), but really don't know enough about windings to check resistance properly.
Is there anything else in the unit that could cause this type of failure? I hate to buy a new motor for $150.00+ and find out that's not the problem and can't return it.
Thanks,
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Old 06-09-2009, 06:36 AM   #5
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How to Troubleshoot A/C Blower motor


Disconnect the belt from the motor and try running different speeds wiith no load. Then turn the squirrel cage by hand and spin , then check the shaft for wobble and side play and LISTEN closely while you do it. It should spin freely and silently You could have a binding in the cage or a bd motor. An out of balance cage with shot bushings will create a big problem but you can generally rebuild them cheap with a new set of bushings and shaft. The motor itself can be taken to a rebuilder for exchange or overhaul, sometimes same day
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Old 06-09-2009, 11:27 AM   #6
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How to Troubleshoot A/C Blower motor


You could also check that when the compressor runs you have at least 216vac into the unit.
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Old 06-09-2009, 07:21 PM   #7
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How to Troubleshoot A/C Blower motor


Thanks for the response and suggestions.......unfortunately, since I don't know much about voltage & resistance checks....I decided to go ahead and get a replacement motor and install it with a new capacitor.....thinking this would "fix" my blower problems. WRONG!!....the A/C unit is still not working! As mentioned earlier....with the thermostat on auto/cool...the compressor kicks on and runs, but the blower seems to "lurch" to try to get going but doesn't kick in all the way. Eventually the compressor shuts off....and the cycle repeats its self when the compressor cools down. When I turn the thermostat over to off & "run" instead of auto, the blower again trys to start...but still seems to lurch or tries to start...without kicking in. What can this be.....maybe the circuit board?
How do I check the voltage to make sure the motor is getting what it needs? Is there a voltage loop back from the compressor that feeds the motor?
Any and all suggestions appreciated......Thanks!!
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Old 06-09-2009, 07:26 PM   #8
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How to Troubleshoot A/C Blower motor


Post the schematic.
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Old 06-09-2009, 07:45 PM   #9
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Quick reply...thanks! Will try to get picture of schematic scanned and posted!

I think I should add to my narative that I initially had a local HVAC service tech come out two weeks ago when system initially wouldn't work. Unfortunately, when he showed up, A/C fired up and everything worked fine. He went ahead and checked system, said "all was okay", confirmed that R22 (or R13, or freon...or whatever is used now) was full and he didn't see anything wrong. Charged a $95.00 service call (seemed reasonable) and left the house with the A/C working. It is now two weeks later and we are going on third day of hot days and nights with no cold air. I probably should have called the service Tech back two days ago...but didn't want to pay potential high cost for replacement components if they were something I can replace myself.
As my wife says...appears to be another situation where it would have been cheaper if I'd just called the professional!
Yoyizit...can you be a little more descriptive and/or informative with your suggestions? What will checking the voltage from the compressor tell me? How can the motor not running be a compressor issue? Would it be more likely a control board issue and if so...is there a simple way to check it?
Thanks,
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Old 06-09-2009, 07:52 PM   #10
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How to Troubleshoot A/C Blower motor


Quote:
Originally Posted by ptcarty View Post
Yoyizit...can you be a little more descriptive and/or informative with your suggestions?
What will checking the voltage from the compressor tell me? 1
How can the motor not running be a compressor issue? 2
Would it be more likely a control board issue and if so...is there a simple way to check it? 3
Thanks,
1 If the voltage to the unit is less than 216v then you might have a wiring problem to the unit.
2 Dunno' until I see a schematic. Maybe the heavy compressor current draw drops the voltage to the fan motor because of high resistance upstream.
3 I'd think bad relay contacts upstream of the motor. This may be independent of the control board since when the compressor is running the fan is supposed to be running.

If you post make and model the HVAC guys here can probably diagnose it without even looking at the schematic. And an Internet search might turn up other people with the same symptoms.

Page 13 of this manual
http://www.goodmanmfg.com/Portals/0/pdf/SS/SS-GMH95.pdf
shows the motor cooling winding having to go through 3 sets of closed relay contacts.
Since relays are almost always either on or off, I'd suspect high contact resistance.

Last edited by Yoyizit; 06-09-2009 at 08:14 PM.
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Old 06-09-2009, 08:36 PM   #11
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How to Troubleshoot A/C Blower motor


You don't happen to have an older round Honeywell thermostat do you.

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