Mach III plus 13.5 ac fan running backwards?
Hello all, My first trip out this year, my 2 yo ac was blowing through the filters and sucking through the vents. I was told it was probably a bad motor starter so I replaced it. Still blowin...
Forum Discussion
Yep, the forward incline blower wheel just blows way less if running backwards. The most plausible explanation I can think of for your motor running backwards is... The motor is a PSC, permanent split capacitor, and if the start cap or start winding is open and the run winding is good, it can start either way but it will be under powered. I'd test the cap and ohm the start winding.
Reversing a psc (and split phase motors) is done by reversing the start winding relative to the run winding and replacement motors can be had with the pigtails to do it. The cap throws the start winding out of phase to the run winding, causing the tq. to start the rotor (in the correct direction) or start it with more tq., with an added start cap and relay, like compressors but PSC blower motors don't use a start cap. It takes a good start cap/winding circuit to tell the rotor which way to run. You can disconnect the run cap/winding circuit and you can spin the rotor by hand, when powered up, and it will run either way, when only the run winding is powered. So, everything can look fine, be wired fine and installed fine but a bad cap or open run winding can do exactly what you're seeing. I always test the cap, first.
Always discharge caps, even if the power has been off. A psc motor with a burnt out start winding can charge the run cap but it doesn't have a completed start circuit to discharged the cap and that cap can hold the charge for a LONG time... and zap you sterile! I've seen it hundreds of times. Craig
Reversing a psc (and split phase motors) is done by reversing the start winding relative to the run winding and replacement motors can be had with the pigtails to do it. The cap throws the start winding out of phase to the run winding, causing the tq. to start the rotor (in the correct direction) or start it with more tq., with an added start cap and relay, like compressors but PSC blower motors don't use a start cap. It takes a good start cap/winding circuit to tell the rotor which way to run. You can disconnect the run cap/winding circuit and you can spin the rotor by hand, when powered up, and it will run either way, when only the run winding is powered. So, everything can look fine, be wired fine and installed fine but a bad cap or open run winding can do exactly what you're seeing. I always test the cap, first.
Always discharge caps, even if the power has been off. A psc motor with a burnt out start winding can charge the run cap but it doesn't have a completed start circuit to discharged the cap and that cap can hold the charge for a LONG time... and zap you sterile! I've seen it hundreds of times. Craig
