Fan motor won't turn... sometimes


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Old 08-07-10, 07:58 PM
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Fan motor won't turn... sometimes

I've got an old Carrier condensor that's been acting up the last few days. Sometimes it'll blow cold air and sometimes it won't. I went outside to look at the condensor when it wasn't blowing cold air and noticed the fan wasn't turning and I could hear a loud humming. I tried the start test by using a long screwdriver to push the fan blade but I couldn't really get it to start - maybe I didn't have enough leverage. One thing I did notice though is that if I turned off the AC from the inside, then I could make the fan blade spin just fine.

My initial conclusion is that the issue is the run capacitor (also called fan motor start capacitor I think) so the fan doesn't have enough power to start - and if I had more leverage, I could probably get the fan to start by pushing it.

The strange thing is that if I leave the unit off for many hours and then start it up again, then the fan will turn iand t will cool the house down fine. Also, I'm not sure but I think it seems to work fine when it's cooler outside - because so far, it's been working fine though the night but usually doesn't work much if at all during the day.

Could any of the experts here comment? Am I on the right track with thinking I should replace the run cap and if that doesn't do it, then replace the fan motor? Can anyone explain why it seems to be working sometimes?

Thanks in advance!
 
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Old 08-07-10, 08:28 PM
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the key

jimbo I think the key phrase is OLD carrier your best bet is to go ahead and replace the motor and capacitor. Most likely it is overheating from your description from a bad (worn out) motor. Typically you will have a allied electric motor company or something similar in most cities of any reasonable size just have them match it up and then make sure that you wire it back in per diagram and you will be fine.
 
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Old 08-08-10, 12:06 PM
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Thanks for the response! I'll replace the cap and motor and hopefully that should do the trick.

Yes, it's O-L-D - 21 yrs old to be exact - the furnace had to be replaced at 15 years and the coil's in really bad condition - but this condenser's been a beast - never blinked once for all these years.

I just a couple months ago put in a brand new system in for the downstairs and am trying to squeeze another year or two out of this old upstairs system because I just can't afford a whole new system right now - even though I know that's what I really need!
 
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Old 08-08-10, 02:22 PM
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Change the capacitor first (cheap). If that doesn't fix it change the fan motor (expensive).
 
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Old 08-09-10, 07:43 AM
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Originally Posted by jimmyq69
I went outside to look at the condensor when it wasn't blowing cold air and noticed the fan wasn't turning and I could hear a loud humming.
Was the compressor running, just not the fan? Or were neither running? That question should be answered before replacing anything.

A motor that sometimes starts and sometimes doesn't is probably OK.
 
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Old 08-09-10, 05:47 PM
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Now Mike has me thinking on that, yeah it could be that the loud humming was not the compressor (ok I may have assumed that was the compressor) but most of the time the bad capacitor will only produce a low hum. Here is my theory: In the daytime when the ambient temp is up the fan motor overheats and locks up, unit is then turned off and it cools off and runs for a while after it has cooled down. It tends to run longer at night when the ambient temps are down. Of course the coils could be packed with dirt here also causing the fan motor to overheat from being overloaded Hmmm Condenser Fan motors are reasonable if you go to a real electric motor supply house to match it up. You may have to do some extra wiring and maybe tweak the mounting but it is always cheaper than an OEM motor. What can I say? I am just a armchair tech here man. Report back on that compressor before you run off to the electric motor store jimbo just in case. This would be the first time I was wrong in about 10 years but as they say the longer you go without something happening the more of a chance there is of it happening. The ODDS are against me I may never break that Guinness record, do not let this happen man.
 
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Old 08-10-10, 10:14 AM
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I went out and listened to it and the compressor is on - and the unit gets VERY hot to the touch when it's on but the fan isn't turning. Looking at the run cap, it doesn't look damaged in any way - at least not like burst caps I've seen before.

I should also add that when it does work, it appears to work just fine - took some measurements and the air coming out is 20 degrees cooler than the air going in. But it seems to be working less and less - last night it didn't work through the night. Been working late at my job so just haven't had a chance to work on this yet - luckily the downstairs AC is working fine and we've got an extra bedroom downstairs that we're using.

Thanks again for all the suggestions.
 
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Old 08-10-10, 11:46 AM
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I would try replacing the fan capacitor.
 
 

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