My craftsman 921. air compressor pumps up to 120 pounds of pressure with no problem but when the motor shuts off air leaks rapidly from around the pressure switch and the motor constantly kicks off and on. Whats the fix for this?
Start your compressor and let it buid up pressure to turn off. then unplug from power.lossen the fill tube that goes from the pump to the tank. when you loosen it. if it leaks air then your check valve is bad and will have to be replaced.
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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.
The problem is lilkely the check valve between the compressor and the tank -- it is alowing pressure to build from tank to compressor preventing the compressor from turning over. Clean, maybe replace, check valve...
This switch is only rated for up to 2 HP at 240 volts and 1-1/2 HP at 120 volts. Using 3 phase power, you can go only up to 3 HP. That would not cause the problem that you discuss, but it is an unsafe condition.
Some Square D switches have a small relief valve so that when the compressor reaches pressure, the motor stops and the relief opens and lets pressure out of the compressor cylinder. Does your switch have that and might that be what is "leaking"? I believe that if the compressor is tight that the leak would stop rather quickly.
Hi, my name is John. Welcome to FixYa. You have air leaks. Check all lines, pressure switch, line coming from pump to tank. You may have to remove this one to inspect it. Check valve at the bottom of tank. Thanks for choosing FixYa....John
You suspect this unit as being a two stage because of the unusually high cut off pressure. It is a single stage and the motor really has a difficult task and is being pushed to the limits. to reach this pressure. We usually reset the pressure to lower setting ~~ say around 140. Your pump probably has a leaking intank check valve (brass fitting at tank) or leaking valve plate in pump. Simple tests : with pressure in tank unplug compressor from outlet and listens for air leak around pressure switch. As you unplug the running compressor from outlet you should hear air leaking from pressure switch for just a moment as air is let out of airline from pump to tank. If air leaks out till zero pressure then change the valve. If tank holds pressure then valve probably ok. Next test, with no air in tank and air filter removed, plug in compressor and feel intake port for strong suction. If the valve plate is bad, suction will decrease as pressure neers the 120 mark till the point of feeling that air is actually blowing out of intake. With good valve plate there will be strong suction untill unit reaches set pressure. If valve plate is bad also change the cylinder and piston ring. Good luck with your repair.
remove pressure control cover little black box by air connector and check that switch assembly is clear of dirt and not damaged or apart than run compressor and turn adjustment to desired shut off pressure
The pressure switch will shut off when the set pressure is obtained. Usually about 100 to 120 lbs. If the compressor stops at lower pressure than mentioned you may try to adjust the pressure by looking under the switch cover for adjustment screw/nut.(no more than a few turns) Increase pressure by increasing spring tension. Quick cycling is usually caused by air leaking from tubing, drain valve or check valve. After compressor shuts off unplug it from the outlet and spray soapy water on all fittings and drain valve. Repair leaks and test for quick cycling, however the compressor should reach 100-120 before shutting off. Some small compressors have a thermal reset but that usually takes a few minutes to reset. Pressure switch is defective if it shuts off before setting mentioned. Enjoy
Most compressors have a check valve installed in the tank that allows air from the compressor to enter the tank and not allow back pressure to the compressor. Also there is an unloader valve at the pressure switch that activates when the pressure switch cuts out releasing the pressure in the line. These two devices allow the compressor to start in an unloaded condition so that the motor will not strain. When you place you finger on the intake, the compressor is no longer pumping air thus there is not load on the motor. Your problem may be the intank check valve or the capacitor may be weak or bad. Simple check for both. Many volt meters have capacitor check and amp draw. The capacitor should not be more than 10 percent or rating. enjoy