3 Phase 7.5 HP air compressor overheat, runs on and off, we found it has no capacitor, what is the correct capacitor needed.

Question edited for clarity.
Question moved from heating and cooling.

Absolutely the capacitor issue would make it run backwards. The purpose of the capacitor is to give the motor a high amperage jolt boost to get it turning in the right direction when you turn it on. It sounds like yours has a Start Capacitor and a Run Capacitor. Change them both. If one has failed, the other will soon follow.

https://blog.orientalmotor.com/what-does-a-capacitor-do

What is the Purpose of the Capacitor for Motors?

The purpose of the capacitor is to create a poly-phase power supply from a single-phase power supply. With a poly-phase supply, the motor is able to:

1. Set the rotation direction.
2. Provide starting torque for the motor and increase torque during operation.

https://www.google.com/search?q=INGERSOLL+rand+2475-e,+capacitors

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you can not use capacitor.
Running a three phase motor on single phase power is simple. First you'll need to invest in a variable frequency drive.

if the heading is correct ,it is a 3 phase unit
they will not run if a phase is out
check all circuit breakers
have an electrician check the motor for a failed phase

It might. Mounting holes match? Shaft diameter and adapter match? Power supply sufficient for 5HP motor? It's a big motor! You might get a better answer from the ebay supplier.

The resister soldered between the two leads of the capacitor is not really needed for operation. This resistor just bleeds down the charge of the capacitor when the compressor is off. Could you re-post with the problem that you are having with the unit.

Your 3 phase unit should not have a capacitor. I'm guessing it's single phase. If it's a single capacitor than the compressor should not be going to it also. To test the motor, common to start plus common to run should equal the ohms you get between start and run. For instance, 1.2 ohms+ 2.2 ohms= 3.4 ohms. Follow the wiring diagram on the inside of the door, send model number!!

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Yes, this compressor will work with single phase motor. Stephen.

You will need a rotary converter for this, or a single phase motor. A three phase motor absolutely cannot be made to run on single phase otherwise.

i think you have a bad phase or you are not getting the correct volts going in try switching the hot wires red to black and black to red and check each set of windings for continuity

I believe your capacitor or capacitors are going out. Or one of the three phases has popped a fuse.

If there is a fuse box for the unit, shut off the breakers on the wall to the unit and do a continuity test across each fuse.

If nothing is found, remove all motor capacitors and bring them into you local electric motor repair shop. Usually they will check capacitors for free.

This should do it.