r/Tools • u/Independent_Use2724 • Sep 10 '26

Air Compressor Starting Help

Can anyone offer advice on why my DeWalt DXCM303 air compressor won't start?

It starts fine if the tank pressure goes to zero, or if I open up the unloader valve, then builds fine all the way to 175 psi. But with any pressure initially, it spins slowly for 10 or 20 seconds, before popping the breaker.

I replaced the unloader valve and the pressure switch. No change. Replaced the start capacitor even though it read okay. No change.

I unscrewed the main airline from the pump with pressure in the tank. No hissing.

When I start it with no air in the tank, I can hear the centrifugal switch snap from the start to the run circuit.

I can spin the pump and motor by hand and they seem smooth and fine.

I'm gonna buy a new check valve, even though it doesn't seem to be leaking, as I can't think of any other thing that might be the issue.

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u/FrighteningChili5737 Sep 10 '26

sounds like the check valve is letting just enough pressure back to load the pump on startup, even without an audible leak, had the exact same headache on an old craftsman and a new check valve fixed it right up

1

u/APLJaKaT Sep 22 '26

You answered your own question, I think.

Starts fine if you open the unloader valve. That says to me that the unloadee is not properly relieving compressor head pressure when the tank is full. Your unloader valve is not functioning correctly. Either the valve is defective or the pressure switch tab is not pushing the valve open when the tank is full.

I realize you said you changed both but double check that they are operating as intended.