Sanborn Magna Force Air compressor

[candjcycles]

I acquired this Sanborn compressor on trade. I think the motor is trash. I was wondering if anyone might have some good advice as to where i could get an inexpensive used motor for this. I was thinking of replacing the motor with one of the Smith+Jones motors from Harbor freight but they are $119. The compressor isnt worth that. Any advice would be greatly appreciated.

 

[6PTsocket]

What have you done to verify that the motor is trash? Have you checked out that motor start capacitor? Is the cenrifugal switch working? Is the comoressor pressure switch good? These problems are far more common than burned out motor windings. Who took the cover off the start capacitor?

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[Zeeman]

Find out if the motor is indeed bad like 6PT said. If it is, look for an old machine on CL that has a motor like you're looking for, or you might find just the motor on CL.

 

[candjcycles]

When the motor is unplugged the pulley spins freely but when the motor is energized it seizes and only makes a humming noise. I used fine sandpaper and cleaned the contacts. I also applied some oil to the centrifugal clutch shaft to make sure it moves freely. The inside of the engine is filthy and appears worn out at first glance. I have not tested the capacitor yet. I removed the cover for the capacitor, i discharged it right away. I am going to test the capacitor now. All the advice is appreciated. I am really enjoying browsing the forum. Thanks.

 

[6PTsocket]

When the motor is unplugged the pulley spins freely but when the motor is energized it seizes and only makes a humming noise. I used fine sandpaper and cleaned the contacts. I also applied some oil to the centrifugal clutch shaft to make sure it moves freely. The inside of the engine is filthy and appears worn out at first glance. I have not tested the capacitor yet. I removed the cover for the capacitor, i discharged it right away. I am going to test the capacitor now. All the advice is appreciated. I am really enjoying browsing the forum. Thanks.

It is a start capacitor that gets the motor spinning under load. With the belt off and the cap disconnected, in case it is shorted, you should be able to give the motor a push, by hand to get it going. If not, something else is wrong. If it goes, it may well be the cap.

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[candjcycles]

I picked up a start capacitor for $8 from the appliance store and swapped it. There was no change in condition. I disassembled the motor to see if there was any obvious signs of failure. Here are some pictures of it disassembled. It is pretty worn out.

 

[candjcycles]

One more.

 

[candjcycles]

I tested continuity on the pressure switch closed and open. It has continuity in both positions. From terminal to terminal on the switch there is very little resistance measured. I havent tested the voltage on the 2 terminals when the compressor is plugged in. I will test that tomorrow. Is there anything i am missing? It seems like the issue might be in the switch. Thanks. I am really enjoying the forum.

 

[gungatim]

looks like someone used it to paint a car in their garage...***** in paint and coats it up. my guess is the switch if there are no breaks in the wires and the winding is good.

 

[candjcycles]

Thanks buddy. I am thinking the switch is the problem too. Not sure how this thing was treated in the past. You may be right.

 

[Packard V8]

Doesn't appear to be the original motor and pulley for that compressor. IIRC, the correct motor had two external capacitors. What is the RPM of that GE motor? I once saw someone put a single capacitor 3450 RPM motor on a compressor. It soon burned up.

Does the compressor turn freely?

jack vines

 

[candjcycles]

Im pretty sure its the original motor. 1750 rpm, 1/2 hp, 115 volt. The compressor turns ny hand when off. When power is on it siezes. All it does is hum when it is on.

 

[6PTsocket]

Doesn't appear to be the original motor and pulley for that compressor. IIRC, the correct motor had two external capacitors. What is the RPM of that GE motor? I once saw someone put a single capacitor 3450 RPM motor on a compressor. It soon burned up.

Does the compressor turn freely?

jack vines

Many compressor motors have a start and a run capacitor but not all. Google "compressor motor" and you will see 2 and 3 hp motors selling for several hundred dollars, with just one cap. I saw a couple of Marathons sold by Zoro when I just looked. Your friend's motor was probably not designed for the high starting requirements of a compressor. The starting capacitor helps with that. The internal design of the motor detirmines whether a run capacitor is needed.

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