Blower fan intermittent on AC only

Model of my unit is GMS80704BNA. After my air conditioner runs for an hour or two the blower will start cycling every minute or so from turning off to running at roughly 1/2 power and continue until I shut it off at the thermostat and wait awhile. I don't know how long of a wait, but more than a few minutes. When it is doing this routine if I switch it to fan only then it still cycles. If I have waited the appropriate amount of time then I can turn on the fan only and it will run forever, or at least over a day straight. I have tested this three times because that is what is really confusing me. It also works fine on heater. I had this problem at the end of last year and it made it through the winter with no problems until the first time I turned the air conditioner on this year. I would greatly appreciate any help. Thanks.

 

I would try running the A/C until the blower fails. Turn the system off at the safety switch, open the blower door and carefully feel the blower motor. If it's real hot it would appear it's failing. Most likely worn out bearings.

Since heat uses a lower speed.... the problem may not be as obvious.

 

Man these guys are giving good advice it sounds like the cooling speed winding is weak on your blower motor from everything that you have stated so far. Only other thing I could think of would be a duct restriction which creates too much back pressure on the fan causing it to kick out on overload? Are you getting good airflow from all the vents when it runs?

 

I would verify that the system isn't cycling on a float switch due to a partially restricted drain, measure the run capacitor to the motor if it is a PSC motor then measure the voltage from the control board to the motor.

 

Wow I am impressed houston knows his stuff. That makes perfect logical sense and would be the next logical step. Just goes to show you that 2 heads are better than one...

 

Thank you very much guys for the input. It's hard to ever get any answers in most forums. Talking it out, no matter what the problem or situation, helps tremendously. Please keep in mind I am in no way a heating/air guy, but I can work things out and fix things. The unit is in the attic and before the drain even goes through the ceiling, the pipe is sitting inside a larger diameter one, so I would have to assume it's not a drain issue. PJmax said the heat blows slower, but does the fan only blow slower than the A/C? I have always assumed they were the same. I just spent awhile comparing and it sure seems that the A/C blows about 30% harder than when it is set to fan only. If this is the case, then I would have to agree totally that it is a weak motor.

 

Usually the heat uses the medium or medium high setting.
A/C and FAN ONLY use the high speed fan setting.

 

After just noticing it had failed again, I felt the motor, and two seconds was the max I could keep my fingers on it without feeling they would get blistered. I don't know how hot they typically feel, but that sounds like a bad motor, right? I still don't get why the FAN ONLY will run constantly without ever cycling off, but whatever. As long as we got what part it needs figured out.

 

Well, I replaced the motor last week. I haven't had to run the AC much, but I never noticed it shutting off or blowing weak. I really felt like it was fixed. Last night I noticed when I walked under the return vent that is was about half as loud as normal and sure enough air was just barely coming out of the vents. So, how hot should the motor typically feel? As I stated in my last comment, two seconds was the absolute max I could keep my finger on it. Do you think I just got a bad new motor or do you think something else entirely?

 

Ok. I have something new to add that hopefully will be something obvious to you guys. I ran it on FAN ONLY for a couple of hours and then felt the new blower motor. It felt cool. I ran it on AC for an hour and when I went to unplug the power cord going to the unit, the cord felt hot at the outlet. The new motor also felt very hot.