AC Fan not working

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Pointerman

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My AC/Heater fan is not working.  When I turn the fan on I hear a faint bug coming from the main vent.  Any idea what might be wrong?  How do I trouble shoot this system?  I'd hate to have to sink a bunch of money into dropping this at the RV shop.  Should be able to fix this myself.  Thoughts?
 

Dogbone

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Villa Rica Ga.
could you try turning the fan it could be stuck  from not being ised... but then that will depend on if it hasnt been used for a while...
 

bigskymt

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  You didn't mention the type of vehicle you have. Have you tried various switch positions or vent settings? (in case switch contacts or rheostat is bad or a vent door is pushing weatherstripping into the squirrel cage). If you can locate the heater box you might try hitting it. On many vehicles the fan motor assy. is easily accessible mounted in the heater box.
 

rvpuller

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Take the cover off your a/c unit and see if the fan will turn freely, if it does then grab the shaft and see if it has up and down movement. If it does the bearings are bad and the motor will have to be replaced if not have someone turn one the fan and if it won't start carefully give the blade a spin and see if it will start to run. If it runs slowly it could have a bad run capacitor or a bad start winding. The motor will have to turn over very freely to be able to start and run on its own, very few have a place to oil them anymore so if the bearings are tight the motor will have to be replaced.

Denny
 

Gary RV_Wizard

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If you have two a/c's, you can swap parts (start capacitor, fans) to see what is the problem. Then buy the part you need.

Some good possibilities are: (1) the fan blade is hitting the shroud (may be worn or corroded shaft has let the fan blades move), (2) motor bushings corroded or (3) fan start capacitor
 

Pointerman

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The AC is a roof top unit on a TT.  I'll have to take a look tonight to see the model.  Does this unit blow the air for the heater as well, but neither function is blowing anything.
 

bigskymt

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  I initially responded thinking it was a dash air problem. You should be able to remove the bottom cover to inspect inside. Try using just Fan w/o A/C. The heat function is usually just a heat strip in the unit. One fan does it all.
 

Pointerman

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I tried using the fan only.  Switched the thermostat to fan "on".  That is when I get the buzzing sound with no air flow at all.  Last time unit was used was in December.  It has been sitting for a few months.
 

bigskymt

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  You'll have to remove the lower cover. I assume it's not ducted A/C. Once you get at the fan you can try to move the blades by hand, w/o power of course.
  I'm curious, if you try A/C does the compressor and fan turn on? That would eliminate any power faults at the unit.
 

Gary RV_Wizard

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There are two fans on one shaft and one motor, one to circulate air inside the rig and one to move air over the condenser on the outside. Either one could be wedged so it cannot move. fans are usually accessible from the top side. A problem with the outside fan is more common - a stick or "critter" gets in there.
 

Pointerman

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Thanks all.  Climbed on the roof, removed the AC cover and a simple spin of the fan solved the problem.  Just seized up a bit.  Probably need to hit it with some WD40 to finish it off.  Easiest repair I have ever had to do (with the exception of the slime on my TT roof).
 

Lou Schneider

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Unless you actually felt resistance, it might not be a sticky shaft bearing.  Those fan motors use a starting capacitor - if it's bad, the motor won't start from a dead stop but will run if you start it spinning by hand.
 

rvpuller

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Lou Schneider said:
Unless you actually felt resistance, it might not be a sticky shaft bearing.  Those fan motors use a starting capacitor - if it's bad, the motor won't start from a dead stop but will run if you start it spinning by hand.

The fan motor in a RV A/C or any other A/C unit I have ever worked on does not use a start capacitor they use a run capacitor that's in the circuit all the time two split the phase. They are a low starting torque motor and need the shaft to be free in order to start. If the motor has a place to oil it oil it but very few do, I would not recommend using WD40 but rather trying to get few drops of oil to flow down the shaft ends. I have also made my own oil hole but you have to know where to drill a hole without damaging the motor.

Denny
 

tennsmith

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I'm with rvpuller (Denny), don't use WD-40,  it isn't a real lubricant.  It's nice that it comes in a spray can and all that, but what you need is a very light oil like 3 in 1 or some other machine oil.  WD-40 has a lot of fish oil in it, but that's not satisfactory as a machinery lubricant.
 

RLSharp

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rvpuller said:
The fan motor in a RV A/C or any other A/C unit I have ever worked on does not use a start capacitor they use a run capacitor that's in the circuit all the time two split the phase.

My Coleman air conditioner does indeed have a start capacitor. See the attached diagram, upper left corner of diagram.

Richard

Edited to "upper left corner of diagram."
 

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bigskymt

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rvpuller said:
The fan motor in a RV A/C or any other A/C unit I have ever worked on does not use a start capacitor they use a run capacitor that's in the circuit all the time two split the phase.
Denny
      My previous duo therms had both start and run caps.
  I've found excellent downloadable schematics at www.bryantrv.com. A Google search will direct you to the downloadable PDF Diagnostic Service Manuals if necessary.
 

rvpuller

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RLSharp said:
My Coleman air conditioner does indeed have a start capacitor. See the attached diagram, upper left corner of diagram.

Richard

Edited to "upper left corner of diagram."

The fan circuit in that diagram does not have a start cap it has a run cap, the compressor circuit does but it also has a relay to take it out of the circuit because start capacitors can not stay in the motor circuit after the motor starts if it does it with blow up. If you ever run across a bad start cap it's best to replace the relay or thermo device at the same time.

Denny
 

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