The compressor starts to surge at 50 psi then blows the breaker took the air cleaner off and checked for obstructions none found .if i put my finger on the air inlet and restrict the intake by half it will build to 125 psi and cut out like it should. i checked the lines to make sure they were clear all seamed fine checked the relief valve it works too . any ideas?

BE CAREFUL! Jump the pressure switch and see if it starts. If so, replace the switch. If it doesn't start but hums, cut the power and try to turn the compressor by hand. Free it up if possible. If it does not hum, look for a reset on the motor or a blown fuse or breaker.

Bad Capacitors

check and test the capacitor or power source --to long or not correct extension cord --to small a breaker for load start

T wo suggestions. 1- check the check valve located in top of the receiver tank by letting the unit pump up to 50 psi. shut it off and loosen the copper tube at the HP cylinder. if no air blows out the check valve is good. If it's bad it will blow until it empties the tank. If the check valve is bad replace it. 2- Tighten the drive belt. If neither corrects the problem remove the guard and rotate the pump by hand. If it's hard to rotate you have a pump problem.

Any idea of HP rating? It doesn't take much compressor to trip a regular 15A breaker.

There is a check valve between the compressor and tank, and there is also an 'unloader valve' which blows the pressure off the compressor so that it starts under little load. I think your check valve is stuck open and the unloader valve is blowing tank pressure off.. and when the compressor tries to start it's starting against the pressure in the tank.

So check/replace/thaw the check valve and you'll be good to go. It's generally at the tank where the line from the compressor head goes into the tank, it'll be between the two somewhere.

lp

make sure it is on a 20 amp breaker

When the pressure switch fails the comperssor will overpressure to the point of safety release at about 150 - 160 psi. It sounds as if your compressor is not producing enough pressure to cycle off at 120 and just keeps running. This happens when air is leaking from fittings or worn cylinder / reed valves. Don't worry, with some simple tests we will find the actual problem. I am assuming that your compressor is oilfree type. If there are leaks the compressor may not reach set pressure. I use soapy water on all connections and on the head/headvalve (remove plastic covers to get to all parts that may leak) while compressor is running. Make repairs as necessary. If still low pressure, while compressor is running and has reached max obtainable pressure (in your case 60 lbs), carefully place finger over intake port hole (remove filter). If the compressor is pumping normally but leaking there will be ample suction at intake and cause the compressor to speed-up when intake is obstructed with finger. If you feel plenty of suction and no visible (soapy water) leaks, then the problem is probably the cylinder /ring is not correctly seating /scratched and air is leaking past cylinder. Make sure that the cylinder /piston ring is properly aligned and that the lip on the vinyl ring is up toward the head. On oilfree compressors you can examine the cylinder by pushing the piston all the way up, then look for scratches neer top of cylinder. If scratched, pressure is leaking past cylinder, install cylinder kit. If you do not feel suction but rather air blowing out of the intake, (do this test when tank has reached 60 psi) then the problem is the headvalve plate/reed valves are leaking. The reeds must seal perfectly on their seats and not be bent or have obstruction. Replace as necessary. If reeds or headgasket is leaking the discharge air will be very hot. Only one other thing to check and that is the intank check valve. Easy to check. Run compressor till you have about 50+ lbs in the tank then unplug compressor. Carefully loosen the inlet hose at checkvalve and listen for air leaking out of tank. (check valve is the brass valve at tank) If leaking replace checkvalve. Use caution when removing head to try and save the gaskets. If you have oil type pump, and no air leaks (soapy water test) suspect reed valves/valve plate. Good luck on your repair and email if you have other question.

You may have a clogged expansion valve.

Don"t worry, even the best techs overlook a thing or two during repairs. Lets go over some basics to determine where fault is located. You will need to do some simple tests. If there are leaks the compressor may not reach set pressure. I use soapy water on all connections and on the head/headvalve while compressor is running. Make repairs as necessary. If still low pressure, while compressor is running and has reached max obtainable pressure (still low 70 - 80 lbs), carefully place finger over intake port hole (remove filter). If the compressor is pumping normally but leaking there will be ample suction at intake and cause the compressor to speed-up when intake is obstructed with finger. If you feel plenty of suction and no visible (soapy water) leaks, then the problem is probably the cylinder /ring is not correctly seating and air is leaking past cylinder. Make sure that the cylinder /piston ring is properly alighed and that the lip on the vinyl ring is up toward the head. If you do not feel suction but rather air seeming blowing out of the intake, then the problem is the headvalve plate/reed valves are leaking. The reeds must seal perfectly on their seats and not bent or have obstruction. Replace as necessary. Only one other thing to check and that is the intank check valve. Easy to check. Run compressor till you have about 70 lbs in the tank then unplug compressor. Carefully loosen the inlet hose at checkvalve and listen for air leaking out of tank. If leaking replace checkvalve. Use caution when removing head to try and save the gaskets. Good luck on your repair and email if you have other question.