Anyone familiar with HVAC troubleshooting?

[Resqueline]

Re: Anyone familiar with HVAC troubleshooting?

If the fan has only two wires, gets full voltage, does not hum or get warm and turns freely by hand then it must be broken somehow. What's the voltage across the cap'? Also disconnect the motor and measure the Ohms in it if you can.

[delaware74b]

Re: Anyone familiar with HVAC troubleshooting?

It sounds like the motor may have gone bad with open windings or the capacitor is bad. Motor caps usually bulge when they short internally. The cap could also be open. I agree with Requeline, ohms check your motor. Also, if you can, test your motor cap, it generally needs to be within 10% (6.75 to 8.25 uf).

[Krankshaft]

Re: Anyone familiar with HVAC troubleshooting?

Whoops I lost track of this thread. No motor hum when voltage is applied sounds like open windings in the motor. If so the motor should be replaced.

If the motor hums and there is no rotation that means a bad motor start cap and a hand spin should get it going.

However if the start cap was bad the motor wouldn't start and you unknowingly let it hum (generates tons of heat) then yes you'd burn the windings out that way.

But from my understanding most motors have automatic (or switch reset if your motor is older) thermal overload protectors to kill power to the motor if the windings rise above a certain temp.

[delaware74b]

Re: Anyone familiar with HVAC troubleshooting?

Krankshaft- I've seen thermal fuses in the windings of motors, especially fractional horsepower. They work but they are non-resetting. Usually they are in motors for small fans (portable 12 + 20") or in small heaters including wall-mounted heaters.

[ausheaven]

Re: Anyone familiar with HVAC troubleshooting?

When was the last time you gave the filter and the fins a good clean?