I have a problem with my 4 hp cambell hausfeld oiless direct drive air compressor. When empty it will start and work fine but if there is 50 + psi in the tank the motor tries to start and the thermal overload keeps tripping out. I checked the check valve and it is clean and moves freely, also the unloader valve is clean and seems to work fine. Could the problem be in the motor, or its capacitors? Any other ideas? Thanks
Sounds like the pressure switch to me. You already ruled out the motor and capacitors yourself by saying that it works fine until there is 50 psi. That tells me the pressure switch is faulty
Searcher1
That sounds like the compressor isn't unloaded. Either because the unloader isn't functioning or because tank pressure is leaking back into the compressor. You should be able to find out what's happening by cracking the output connection right after the unit cycles off at pressure. Evidence of high pressure release would indicate that the unloader isn't working. Cracking the output connection after the unit has sits a while with the airtank above 50psi will tell you if there's leak back.
It is also possible that there's a motor problem. Swapping out the start capacitor would be a pretty cheap diagnostic.
If the centrifugal start switch was stuck in the Run position, it would never cut in the start windings when it spun down - do you now hear a distinct "click" as the motor starts up, and another as it coasts to a stop?
It might have been able to start the motor on the Run windings alone with no air pressure in the tank, but with any backpressure at all past the check valve it wouldn't go. It wouldn't reach speed before the tubing between the compressor and the check valve pressurized and stalled the motor.
I had to cheat to make an airbrush system out of a 1/3 HP diaphragm compressor that could not start reliably against head pressure - used a 10-second cam-switch motor sequencer, a self-latching (drop-out) motor relay and a solenoid valve for the unloader. Leaving the unloader valve open for 5 seconds after motor start (until the motor came up to speed) allowed it to work every time against a tank and check valve.
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He did say it was a campell hausfield oilless in the first post. Not only does it sound big, sound is the only big thing about it; there's yet another useless lawsuit where you get a worthless coupon to buy more cheesy crap (rather than actual money) if you were so silly as to buy one of many compressors with "horsepower" that was a complete lie.
He said 4 hp but they list them by model # so all I could find was Portable Direct Drive info If it were my unit I would zero in on the unloader. Don't know much about air compressors .... I'm an x CNC service engineer
Tom
I have a similar situation: the compressor has a difficult time starting and if it's cold, it won't start at all (labors slowly along until the breaker trips). The only way that it starts instantly is if the outlet from the compressor head is disconnected. I *definitely* ruled out the unloader and the check valve. BTW - the check valve cannot be the problem if the unloader is working: the unloader drains the pressure between the compressor and the check valve. A bad check valve would just bleed down the tank through the unloader. The capacitors are ok on a go/no-go basis (not short or open).
When I saw "habbi's" post I checked my centrifugal switch. It was pitted, so I cleaned it. When I tried it, I noticed a lot of arcing during start (it still didn't start right up). It was "hunting": at stop the switch is closed and it gets *almost* to speed and the switch opens. Which causes it to slow and re-close the switch. This repeats. When it has warmed up it doesn't do it.
So, at cold the load is too much for the motor to get to speed before the centrifugal switch opens. Which means:
BTW, this is a small IR compressor, "2 hp" motor (15a at 110).
Bob
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