the pressure switch doesnt kick off at the max pressure

by Matt
(Waukee, Ia)

I put a new pressure switch on my compressor, it still goes past the max pressure. so i have to switch the breaker off. when it does eventually shut off the motor hums and doesnt want to start.

Matt, if you put a new pressure switch on your air compressor and the pressure in the tank exceeds the normal cut out pressure, a few things come to mind.

When you acquired the replacement, were the set points the same as the old pressure switch, and if not, did you adjust the new switch settings to mirror the old?

Or, the pressure switch points typically open when the diaphragm in the base of the switch experiences the set point pressure. If the set points are not opening, then you either have a bum switch, or the wiring is incorrect.

When you installed the new switch, did you reconnect the unloader valve? A non-working unloader could be the reason the compressor will not start on it's own if there is pressure in the tank.



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Pressure relief switch

by Fred Kaier
(Phoenixville PA)

When my SEARS compressor shuts off, air is leaking from the pressure control switch. (brass fitting with an actuator pin on the bottom of the square D switch box) The only part # I can find on the switch is CAC-4336.what is the replacement part and where can I get it?

Bill answers...

Hello Fred:

While air may be leaking from the unloader valve on your pressure switch, I don't think it's either the unloader valve or the pressure switch that is your problem.

There's a check valve in the line from the head to the tank, and it's purpose is to keep the air in the tank once the compressor unloads. If that leaks, all of the air in your tank will bleed out the unloader valve.

Here's more info on this issue.



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Apr 15, 2010
Hitachi EC12 2HP Twin Tank 4 Gallon Compressor
by: Bill

My twin tank Hitachi EC-12 was leaking down thru the unload valve, I think. So I bought a new press switch with new brass unload valve installed it and to my disbelief it does the same thing. In addition, once the tanks are beyond 90 psi the compressor will stall and just hum until I allow the air to bleed down below 40-30 psi. Could it be the check valve, press switch or unloader? Where is the line check-valve located on this Japanese wonder of engineering?

Thanks- Bill

Bill says...

Howdy Bill.

The check valve is usually located where the line from the compressor head enters the tank. That fitting often has an integral check valve.

Make sure the check valve is working... that should stop the air dumping from the pressure switch, and if that's solved, come back to us with the humming... hmmmm?



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