I have a 5hp 16gal. 135 max psi. The compressor builds up to about 50 psi. But no more. The compressor continuously runs never shutting off. I can hear no leaks. Also the on/off switch runs in the off position. You have to unplug to kill motor. I guessing maybe this is the "pressure switch" problems. But just wanted a expert opinion. -thanks

the pressure sensor is likely defective. How old is it? take it to a Dewalt service centre

Hi
your pressure switch is bad. so it isnt cutting off the compressor. the part number is N003306SV and can be obtained from Dewalt on Servicenet.
Detail

Good luck and hope this helps

The motor will run until the pressure switch detects approximately 150psi in the tank. If it never gets to 150psi, it will continue to run. If you are not getting over 50psi in the tank check:
1. that the drain valve on bottom of the tank is fully closed. Don't use a wrench on it but it must be tightly closed by hand.
2. that you don't have any air leaks on the top end of the compressor or on your lines going out of the tank.
If these are OK, your problem lies either in a damaged valve plate or cylinder/piston. You can remove the head and check the condition of both the cylinders and the valve plate. All reeds on the valve plate have to be in good condition with no bends, cracks or warpage from over heating or debris from using the compressor with no air filter. The cylinders should be smooth with no scaring. If a cylinder is damaged you will have to also replace the rings or piston assembly. None of the air compressor companies make an oversized ring set so you can lightly hone cylinders but you cannot have them bored out oversized to correct any damage to the cylinder walls.

The problem with compressors not building pressure is usually a bad pressure switch or bad regulator. Does the motor shut off at 20psi or does it continue running and not build pressure? If the motor continues to run with no increase in pressure, the you should go over the machine looking for air leaks from your regulator back all the way to the motor. Any air leak while the compressor is running can cause the pressure to "peak" way before the intended shutoff that it is regulated to.

Sounds like the pressure regulator has gone bad. That controls how much PSI your system is aloud to have. If this fails it will not fill to max capacity. I would replace that and all will work just fine.

Please rate

your max pressure switch is faulty, and shutting off the power early. replace switch, check owners manual for location(should be near power wires)

Here are the specs on your compressor:
Electric Single Stage Air Compressor, Motor Running Power 5.0 HP, Free Air Flow @ Maximum Pressure 16.1 CFM, Free Air Flow @ 90 psi 18.0 CFM, Maximum Pressure 135 PSI, Phase Single, Voltage Rating 230 Volts, Current Rating 21.5 Amps, Tank Capacity 60 Gallons, Tank Type Vertical, Height 71 Inches, Length 20 Inches, Width 30 Inches, NPT Outlet (F) 1/2 Inch, 60 Hz
Good luck with your new comressor.

Dont understand the question , does the engine shut off after p-max is met , or does it continue to run , if it continues to run then you have a pressure switch problem

Does the compressor continue to run but not build more pressure? In which case it is an air leak most likely, or does the compressor shut off at 50 PSI? In which case it is mose likely the pressure switch. If it is an air leak you can un-screw the guage and coat with putty or teflon tape and reinstall to clog the leak around the threads..