Is Mastercraft compressor motor AC or DC??

by john
(Waterloo, Ontario)

I have a small 2 gallon Mastercraft compressor (058-7936-6) (1/3 Hp) that I use for small roofing jobs (air nailer).
The motor started to vary in speed when cycling and the brushes seemed to be sparking a bit more that usual. I sprayed WD 40 into the bearing/bushing area and the motor improved for a few minutes and then stopped completely. I took it apart and wired the motor directly to a 120 volt AC supply. The motor tries to turn but just stutters back and forth without completing a revolution. My question to you is that I am now wondering if the motor is a DC motor even though the compressor is plugged into a 120 volt AC outlet. Is there a converter on the circuit board??



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Oct 08, 2016
by: Doug in

There doesn't seem to be a manual for this thing online, but I can say it's almost certainly not a DC motor. If it is, then there would be at least a diode or a diode bridge to convert AC to pulse DC.

Does it do the same unloaded? It sounds like a bad start cap, but it may not have one. In that case, it's probably just bad brushes. If you can clean them up, or find replacements, that should fix it.

But then, it's what? a $40 machine? So not much chance of finding parts.

Oct 08, 2016
Mastercraft 058-7936-6
by: Bill

I wasn't able to find any specific info on this model, John.

I would expect, however, that if it were a DC motor, that the power cord plug would indicate that, with a connector that fit into a DC power source.

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