Ever get those jobs where you think you "know" something can be done, but due to brain cramp, can't figure it out??

With a push button motor starter (1 stop, 1 start. Not a manual button starter but one controlled with coil), connected to a compressor with pressure switch. When the pressure switch opens the circuit and breaks the coil contact, it takes the operator to push the start button again once the pressure drops to get the motor going again.

Argh! the holding contact, I believe there is a way around this..... and can't quite remember how to do this. Wire the pressure switch into the aux contacts?

I think a compressor needs an off-auto switch.

You need an off-auto switch, or a locking run push button

I don't think I would leave it that way. I would fill the holes with a press-to-test indicator and a momentary-off-on rotary selector switch. The pressure switch should have a pressure and deadband or differential adjustment. The Off position breaks path to N.C. opens on P increase, switch terminals. The momentary, "Hand" position, parallels P-switch, to check operation without bleeding the tank. The N.O. aux switch would be used to drive your indicator. Do you have any E-stops in the mix? You wouldn't need any holding contacts unless you were going to use 2 separate pressure switches in series. In that case, the holding contact is in parallel with the low pressure switch. It helps to think of one as "closes on low pressure", and the other as, "opens on high pressure"
Joe

Seems like someone is trying to defeat a safety device ... to me. If there's a high-pressure cut off switch, it's there for a reason. I'm not about to give advice on defeating it.

If you want the compressor to automatically re-start when the pressure has dropped ... well, that's a normal control problem, and would be solved by adding a pressure switch - not by bypassing an existing one.

I'm real close to locking this thread. Did I understand the request correctly?

I didn't read this as an over pressure switch, just the one that establishes proper tank pressure.

BINGO!!!

BINGO!

Thanks for the clarification.

Forget the holding contact

You need to bypass the holding contact entirely, and run the coil directly from the pressure differential switch.

A MAINTAINED contact switch can be inserted anywhere in the control circuit to turn it off.

Tried hooking in the pressure switch control at different points in the control circuit. Same issue as o.p.

This was a customer supplied push button starter. I normally don't use these types for air compressors, and thought there would be a simple way without extensive rewiring, or adding extra parts/contacts/switches to keep the push buttons functional.

As others above have noted, the off/auto switch is what we normally use and best.

If you need to keep your 2 buttons, the cheapest way that will work safely is to add 1, DPDT control relay.
1.) Wire "L" or "Hi" to N.C. "OFF" button to N.O. "ON" Button to relay coil to OLs to "N" or "Lo"
2.) Wire relay N.O. contact in parallel with the "ON" button. (Holding contact for the control ckt.)
3.) Wire "L" or "Hi" to other N.O. relay contact to P-switch with differential to contactor coil. (Normal compressor cycling when control circuit is active.
Add any E-stop switches to Line 1. Just about any starter assembly should have the volume to add a control relay. I can do the ladders up on CADD if you want.
Joe

I don't think you can do this with a 3 wire stop/start unless you add a relay.

A simple toggle switch in a handy box will do to switch the control circuit. It isn't a lot of money.

Here is the partial ladder with the rotary selector switch and indicator.
Joe

Option 2 partial ladder, using a control relay to keep existing buttons.
Joe