Air conditioning won't turn on, just hums

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COMer

COMer

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I tried my A/C yesterday, after not using it since December, and the unit will not come on.  Neither will the fan.  Usually, when I turn the control to fan only, the fan starts right up but now it just hums, and if I try to activate the A/C, either then, or with the auto fan switch on, nothing happens.  It worked fine last month when it was warmer and we used it then.  Everything else electrical in the trailer seems to work fine.  I am connected to 30A service and have a switch that needs to be activated so that I can use the A/C and not the fireplace.  That has been done.  It almost sounds like I am not getting full electrical current to the unit but I have checked the panel and there is nothing tripped.  The A/C is on a 20A breaker which I have turned off and back on which does not help.

Any ideas.  It will be getting warm soon and I sure would like to have the unit back.  It is only two years old and I assume should have many more warm days ahead of it.
 
This happened to both of my units over the past year.  The problem was the same in each case; the fan motor was shot.  When I turned the AC on I could hear a hum, that was the compressor I suppose, but no air blew into the coach.  Subsequent investigation showed the fan motor would not turn.  However, it might be just a fan solenoid in your case so I would check that first.  Besides, my units were nearly 20 years old, yours is almost new.  Good luck!
 
Could be something as simply as a piece if debris caught in the external fan blades. My first check would be to go on the roof, remove the shroud and see if the fan blades can be turned by hand. Do this with the a/c off - you don't want it to suddenly start spinning with your hands in the way.
 
How cold was it when you tried to run the A/C? My home A/C won't run below about 60?, and there may be a similar interlock on some mobile rigs.
 
Remove the filter and with the power off, reach up and try to turn the fan blade.  The bushings are probably seized up.  Although it is the wrong time of the year dirt dabbers love to make large nest on the external fan blades that either block the blade from turning or cause the whole coach to shake
 
I'll go with Luca1369 on this one.  Mine did that and the unit was just a little over a year old.  We tried to lube the fan and motor and everything, but no go.  Still under warranty though, and they replaced the fan.  It worked great for the next 4 years until we upgraded to our 5th wheel. 
 
You were right.  I took the cover off from the inside of the trailer and reached up to the fan (squirrel cage, not blades) and tried to spin it with my finger.  It seemed a little stiff to start but then spun very freely.  I tried turning the fan on (after removing my fingers) and it runs fine now.  And the A/C also turns on and operates properly.  Apparently, the unit will not turn on if the fan is not operating.  I've tried it a few times since then and it seems fine.  No idea what caused the fan to seize up but it did and now it isn't.  I'll probably climb up there when it stops raining and see if the fan is permanently lubricated or if I can lube it.  So, thanks for the suggestions.
 
COMer said:
You were right.  I took the cover off from the inside of the trailer and reached up to the fan (squirrel cage, not blades) and tried to spin it with my finger.  It seemed a little stiff to start but then spun very freely.  I tried turning the fan on (after removing my fingers) and it runs fine now.  And the A/C also turns on and operates properly.  Apparently, the unit will not turn on if the fan is not operating.  I've tried it a few times since then and it seems fine.  No idea what caused the fan to seize up but it did and now it isn't.  I'll probably climb up there when it stops raining and see if the fan is permanently lubricated or if I can lube it.  So, thanks for the suggestions.
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Well, I hope you succeed.  I did not.  And again, mine was under warranty, so they replaced it.  But before I took it in, I tried at least 3 times to lube different parts of it.  None of it succeeded.  I've heard the same from others, but maybe you'll have more luck.
 
COMer said:
I took the cover off from the inside of the trailer and reached up to the fan (squirrel cage, not blades) and tried to spin it with my finger.  It seemed a little stiff to start but then spun very freely.  I tried turning the fan on (after removing my fingers) and it runs fine now.
Click to expand...

Mine did the same thing.  At first, I could turn them and get them started, and they started a couple of times by themselves after that, but then they quit permanently.  I did not know that I was supposed to lube the fan motor bearings/bushings on a yearly basis (according to an AC tech).
 
Gary RV Roamer said:
I'm no a/c expert, but the couple of RV a/c's I've worked on had sealed bearings on the fan motor.
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Mine were 20 year old Colemans.  On each end of the fan motor, where the shaft exits, were two small, plastic, yellow plugs, one on each side.  They are easily removed so you can inject lubricant and then re-install the plugs, at least that's what the AC tech said was their purpose.
 
I want to be where you are that you are using A/C...it is 6 degrees here!  No need for air!!
 
We're in Tampa and haven't needed it much recently.  But I have great confidence that we will.  It's been in the low 70's and when the sun hits the trailer, it can get a little stuffy. 
 
I am in Central PA and it was 4 below this morning!  Keep cool...we are.
 
Our home is in NW PA and your report is exactly why we are in Tampa.
 
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