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The Blower motor on my AC unit turns off at random times while the outside unit continues to run which is causing the coil to freeze up. The blower won't come on for 30-45 minutes after the AC has been turned off, but after that it seems to turn back on fine. I have been trying to track the problem down for the last couple months, but it literally only happens every 2 or 3 weeks.

Last night it stopped again and I tried to just turn the fan (from the thermostat) on without luck. I took a look at the blower and it seemed to turn just fine. I put my hand on the back of the fan motor and it wasn't hot to the touch.

About 45 minutes after it turned off the blower came back and it was working normally. What could be causing this problem?

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Do you see this issue in heating mode as well? How old is the furnace and A/C unit? When is the last time you changed the filter? My best guess would be that the blower motor may have bad bearings or other issues causing it to draw too much current, causing the overcurrent protection on the motor to kick in and shut the motor off. It's hard to diagnose without being able to actually take some measurements (and not knowing make/model of the unit), so that's just my first guess. My advice is to call in an HVAC tech, and have them take a look. –  Tester101 Sep 5 '12 at 11:44
    
The filter was a replaced a couple of months ago, the air handler and AC are ~6 year old Goodman. We have never noticed an issue with the heat before but we don't use the heat much in the south. I would think if the fan motor was drawing to much current it would be pretty hot to the touch. I am trying to avoid calling a tech out. –  stoj Sep 5 '12 at 12:10
    
Troubleshooting HVAC systems through the internet is very difficult, any advice you get is going to be a guess based on the information you provide. Providing the most information possible, will allow us to make more educated guesses. Make/Model and/or a schematic will be useful, but nothing beats being able to physically check the system. An HVAC tech will diagnose and fix the problem in a few hours, where it might take days and lots of back and forth for folks on the internet to do it. –  Tester101 Sep 5 '12 at 12:34
    
Stoj, Thanks so much for posting your solution! This had been driving me nuts for quite some time. Same problem and knew there had to be a simple solution. I am a stalwart diy guy and would have hated for an hvac guy to strip/clean my dirty wire & charge me $80. Thanks again –  user25451 Sep 23 at 16:03

5 Answers 5

Also check your ground. I just ran across an intermittent blower issue (cycling on and off constantly during call for heat from the thermostat) that was due to a poor ground connection on my 120 volt to 24 volt transformer on an old Janitrol furnace. The ground side of the 24 volt half of the transformer had 2 wires connected to it. The good one went to the mounting screw of the transformer. The bad wire went to the circuit board. It was bent over perpendicular just above the connecter, and many of the strands were broken. There was also some minor corrosion. Replacing these ground connections resulted in satisfactory operation. This was difficult to troubleshoot because operation was okay if the air filter was not in place, and the issue showed up only when an air filter was installed on the supply side (dirty or clean filters both had the intermittent problem).

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Check your drain lines for water run off. Make sure they are clear and then check the float for the excess water shut down reset them

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I have a ruud rheem heat pump, I had this same issue. The unit was installed in 2006.

After going through the typical steps of checking air filters and electrical components on the unit, I found the wiring from the thermostat for the blower control to the control board was rusted in the wire nut. I cut the wires and stripped them back and reconnected the wires and the AC unit is running with out any trouble now.

Remember to keep it simple. HVAC service companies love these type of calls that an experienced tech can track down quickly. If you have a basic understanding of how circuits work you can fix this easily and save a bunch of cash.

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My central AC unit decided to stop on the hottest day of the year. It would start and run normally for a few minutes and then the blower would shut off. After checking the breakers, thermostat and overflow shut off (did not have one) I saw something about a blower motor capacitor. This was easy to get to and replace and my last hope before waiting for someone to come fix it. The capacitor cost $4.04 with tax and had my AC working again. Needless to say I was beyond happy. I hope this can help others with a similar problem.

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You could improve this answer by providing a link to the information you found about the blower motor capacitor. Where did you buy the capacitor -- Home Depot, Radio Shack, specialty HVAC store? –  Niall C. Jul 9 '13 at 16:33
    
@NiallC. Last time I needed to buy one I bought one off of Amazon. I would be interested to know if there are local places that stock this rather large capacitors. –  stoj Jul 10 '13 at 0:46
    

I ended up calling a buddy of mine who is an HVAC tech and he pointed me in the right direction to check the fan wire on the back of the thermostat. I checked the wire and it was just hanging in the terminal. I'm pretty sure that was the cause of the problem. It makes sense because there wasn't anything wrong with the blower motor itself.

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