Heating, Air Conditioning, Fridge, HVAC/Air handler fan runs iratically


QUESTION: My air handler fan spins erratically. It doesn't spin constantly.Fast and slow.
  I shorted the R and G terminals at the Thermostat and it still reacts the same. I changed the control relay and transformer...same result. The voltage at the control relay when A/c is on is 24 for one wire and 15 volts on the other coming from the transformer.
The fan spins freely when pushed by hand and the voltage  to the fan is 257 volts which I know is high but it wouldn't make the fan react like this I don't think. Outside unit runs.
 I took out the motor and tested it for short against the body (none) and the ohms were all the same for all three connectors so the motor 's fine.
So I'm guessing the control on top of the motor is bad. What am I missing? Motors cost $3-4 hundred dollars Tell me there's something else it could be PLEASE!!!

ANSWER: Since you did not indicate, I do not know what kind of motor you have.  From the what I can gather from your question, it appears you may have an x13 type motor.  If you take a picture and reply with it I can confirm this for sure.  However, if it is in fact an x13 or an electronic type motor, the motor is no good and going to have to be replaced.  Unfortunately, they are very expensive motors and can not be repaired.  


---------- FOLLOW-UP ----------

QUESTION: This is, in fact, an x13 motor. When I took out the blower assembly and took off the motor to check it, it said x13 on the label.
 As I stated before, the motor itself tested fine, but it had the electronic "cap" on it that I didn't know how to test.
 I was hoping that the 15 volts I measured  from the control relay to ground(from the transformer)had something to do with it since it was supposed to be 24 volts.
 Any thoughts on why only 15 volts?  One tap off the transformer goes to the control relay. The other has three taps off of it. One to the control relay ,one to the motor on the same plug as the 240,and one to the heater.
 If I want to turn on the motor directly, how  do I go about it?

The transformer likely has 5 line connections.  They are on the high side for 208, 240 and common.  The low side has two.  The high side it selected for the voltage you have in your home.  Once connected to the high for the correct voltage, the low should be around 24-27v.  You are not clear on what "tap" off the transformer is going where, so I am a bit confused.  The low voltage side of the transformer is going to have one side that goes to ground.  It is attached to the metal casing in the unit.  The line side goes to the control board and t-stat etc. You should measure the voltage on the secondary side of the transformer with nothing connected to see if you have 24v.  With the high voltage wires and ground connected to the motor and one leg of the transformer connected to ground, you can take a wire from the transformer to the one of the 1-5 numbered pins to see if the motor will run.  I am not sure why you are only seeing 15v.  You need  to double check your wiring.  BTW, the connections you see do not go directly to the motor windings and testing with a meter does not mean much.


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Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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