Contactor overheating

[Malcolm McLeod]

... the symbol for an overload heater. It is just a sensor. It's not a switch. ...

Never too old to learn something; years ago I was told this schematic element 'opened', and have never questioned it. But thinking back, I've never taken an OL apart to actually look. My bad. Again, I just get to help trouble-shoot, then point an electrician at this end.

My end is the automation - a BSME corrupted by The Dark Side. One stormy night in my youth, someone pointed me at a what appeared to be a 300lb wire bomb after detonation, and said "Fix it!" ..."What is it?" "A PLC!" ..."How do you spell that?" And there has been no escape.

[Thomas C Barron]

There was zero pressure on the switch. I bled the tank down until it was empty. It then took about 5-10 minutes before it would start back up without me holding the contactor reset button down.

[Thomas C Barron]

Here’s a picture of the contactor. The compressor is a 2002 model year, and it does NOT have a low oil sensor. It appears all original.


I have had the unit for 1-1/2 years, and yesterday was the first time I ever hooked it up. After wiring it up, I turned it on. It took about 3 minutes to pressure up to somewhere around 150-160 psi before shutting off automatically. I wanted to see at what psi it would drain down to before automatically starting back up, so I opened the tank valve to slowly drain out the air. It bled down to completely empty, never starting back up.


I removed the cover to see if I could determine the problem. If I manually pushed in the little square button on the contactor to connect the poles it would run, but as soon as I removed my finger it would turn off. I turned the on/off switch on the pressure regulator to off and walked away. I came back about 5-10 minutes later and when I flipped the switch back on, the compressor started right up and ran to pressure before automatically shutting off...only to complete the non-start after draining the air from the tank again.


This is why I was asking if the contactor could somehow overheat. To me, it acts like the coil that draws the plate in place was getting hot and not working.


I checked and it’s getting 120v power to the line in terminals.


I understand that if the motor was getting hot that the thermal would shut it off...but forcing the contactor closed wouldn’t bypass the thermal circuit and make the motor run...plus, the motor only ran for three minutes total.

[David L Morse]

I understand that if the motor was getting hot that the thermal would shut it off...but forcing the contactor closed wouldn’t bypass the thermal circuit and make the motor run....

Thermal cutoff switch is in the coil circuit so, yes, pushing the contactor closed should start the motor.

I checked and it’s getting 120v power to the line in terminals.

I hope you meant 240V. That motor would draw way too much current on 120V.

[Bill Dufour]

Do you mean the coil was getting 120 volts and not pulling in? I agree the motor needs 240.
Bill D.

[Malcolm McLeod]

Members can’t post pics; you have to be a contributor. At $6/yr, if Creekers can ‘fix’ your compressor without you getting an electrician’s bill, it pays for about 10 years of contributorship. Quite the bargain IMHO.

Do you have the Owners Manual? Does it contain electrical schematic? Can you post pic of it or link to it? Need this if yours is different than George‘s link.

The process to test which device is holding you out is outlined in previous posts - but perhaps modified wire numbers - depending on your specific schematic. ...Best I can offer with available data.

[Malcolm McLeod]

Do you mean the coil was getting 120 volts and not pulling in? I agree the motor needs 240.
Bill D.

Only single phase schematic available so far shows a 240vac coil. Wonder how many varieties I-R offers?

[Thomas C Barron]

I guess I should have said it’s getting 120v to EACH line in terminal.

[Thomas C Barron]

So, today I go in and turn on the compressor and it runs until shutting off at around 168psi. I drained the tank down, and at around 150psi it started back up to then again shut off at 168psi. I repeated this many times with no problems.


I put an amp probe on it each cycle, and it’s pulling about 30 to 31 amps, and cycle time from 0psi to 168psi is 3 minutes 27 seconds. I did not check cycle time from 150psi to shut off.


The only thing is, I did not put the cover back on to the starter control box, and the safety interlock was not being pushed closed by the cover...yet it runs. I’m thinking that maybe the interlock is the culprit?

[Thomas C Barron]

Thank you, every one’s responses were helpful so far.

i bought it used, and don’t have the manual. I didn’t know the thermal was connected to the contactor, so that is helpful to know for future reference.

i will try to post a link to pictures showing what my starter box with contactor, fuses, safety interilock switch and wiring looks like.