Need some help. My compressor motor burned up on Saturday; 7.5hp, single phase, 3490 rpm. I ordered a replacement, a Baldor 7.5hp, single phase, 3450rpm, advertised as made for compressors. Went to install it and found new motor is not wired the same as the old one. Original motor had 6 leads but replacement only has 4. Two extra leads I figure are to energize "latch" on thermal protection contact in compressor control box. Without that latch the pressure switch doesn't get voltage and motor won't turn on. Anyone have any idea how to wire this?

There should be a schematic somewhere......in the box or on the motor lead cover. Without seeing the schematic I can't really help.....

I'll bet you can Google the specific motor and find a schematic online.

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There should be a schematic on the inside of the junction box cover on the motor.

Problem is there were 6 leads and the new motor only has 4. Baldor spec sheet indicates two more leads would be there if the motor had a thermostat, but this one doesn't. Two leads on the compressor go to the controls. Controls don't work with those two leads disconnected. I think if I want to use this motor I need different controls.

Sorry John. But wiring diagrams are like women. I know where to find them. But I'll be damned if I have ever been able to understand them !

I figured it out. The two leads that were on the original motor were for a thermostat, normally closed. Controls would disconnect the power if the motor got too hot. All I have to do is connect the two leads I have left over after connecting the motor, and it will provide "latch' voltage for the contactor. I never had the original motor, in ten-years of operation, shut off due to temperature so I doubt I need that feature anyway. Thanks for all the inputs.

John- as long as the sheeves (I'm assuming you have v-belt drive) are still the original ones and nothing else has changed mechanically, you shouldn't have thermal issues.

Sure, there's some risk, but very minimal, IMO.

The new motor probably has the thermal protection built it. It should have a tp on the nameplate.
Don

Did the old motor actually burn up? Maybe the motor was fine and the thermal switch opened up and disabled the controls. If it did burn up, then the thermal switch wasn't working anyway.

Judging by the extremely loud humming noise and the copious amount of magic smoke that came from the motor, I'm certain it was not the thermal switch. Besides, if the thermal switch opens it opens the contacts removing all power from the motor so there would be no humming nor smoke. New motor runs nicely.