1.7 h.p. compressor motor giving me fits

by Wayne
(Sunset, La.)

I have a 1.7 h.p. motor giving me fits.

When it first starts from empty it will run up to about 70 psi. It will not come on again unless I turn off power and wait about ten minutes.

When I power it up, it will run up to about 100 psi and cut off again.

This is a 150 psi tank.

I have checked the caps, they are good.

I have bypassed the on/off switch and the pressure sensor.

I am running the motor straight off the wall plug.

I would like to check the thermal overloads. They seem to be internal in the motor. Is there any way to check them without disassembling the motor?

Comments for 1.7 h.p. compressor motor giving me fits

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Nov 22, 2015
by: Doug in s.d.ca

If it's like most of the diy compressors, the pump is designed to fit where the the bearing end is, replacing the normal motor - so it's usually just a matter of 4 bolts and nuts, and slip it off (may take some leverage).

Then you may or may not have a bearing on that end of the armature. If no bearing, you may need to take the whole thing.

Be aware that the nuts may be metric.

Nov 22, 2015
by: Wayne

Have you ever pulled one of these motors? I see that the pump is connected to the motor, is it hard to remove?

Nov 22, 2015
by: Doug in s.d.ca

If the caps are truly good, and connected properly, then you have an overload and the thermals are working properly. If you bypass the thermal, you're asking for a fire, or at least a lot of smoke.

Most likely there is an internal short (not necessarily a dead short, but a short, nonetheless) which you need equipment to check, which a motor shop will have.


Nov 22, 2015
Bad motor?
by: Wayne

I reconnected the caps and the motor is still pulling the high amperage, both on start (12.7) and run (continually creeping up until motor shuts down). I've tested the windings to ground and they read almost zero. Still thinking it's the overloads.
What can I check next?

Nov 16, 2015
1.7 fits
by: Doug in s.d.ca

That's too much current, both for startup and especially running.

But you say you "have bypassed the caps..." - that's not good. The caps are required to make the motor run correctly, loaded or not. That's why I asked about them being connected properly.

If you connect the caps and the run current stays that high, that suggests the motor windings may be bad.

Please retest with the caps connected.

Nov 15, 2015
by: wayne

I have bypassed the caps and pressure switch and am running the motor only. Using an ammeter, when the motor starts it's pulling 12.5 amps., the amperage then begins to creep up over 14 amps. then shuts down.
Remember this is just the motor powered up. That's why I'm trying to get to the overloads to replace them.
Do you know if they can be replaced?

Nov 08, 2015
by: Doug in s.d.ca

If the caps are good, are you sure they are connected to the motor properly? You should see voltage across ground and the caps.

Is this a new problem at an old location, or a new location?

You can tell if you have a good power supply by checking the voltage at the pressure switch (or other convent location near the motor - see what the voltage is with it off. Then see what it is with it on. The difference should be under 5%, or about six volts on a 120 circuit.

Alternatively, get a clamp-on ammeter and see what the current is when it's on.

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