Craftsman air compressor 921.153101 has has intermittent trouble starting during regular use. Tries to run but can't get up to speed.

SOURCE: air compressor flips breaker before it will start?

Air compressors tend to draw more power as they age, however, will not trip breaker unless some malfunction. Here are some simple tests. Unplug compressor and turn the pump by hand, you may have to remove a cover to do this. It should turn freely; any resistance could be failing bearing (would make noise) unloader/check valve leaking allowing back pressure to pump, or failed start capacitor/start winding. Easy test for checkvalve. With pressure in tank loosen discharge hose at tank and check for air leak. Check valve should hold pressure in tank. Replace as needed. Failed capacitor/s will cause high amp draw. Remove from circuit and test. UF reading should be within 95% of printed rating. Finally, most air compressor motors have two windings, start and run. Power to windings is controlled by flyball switch inside rear of motor. This switch has contacts that can stick in start position and cause high amp draw. Examine windings for signs of overheating. Copper windings generally have color of new penny. Very dark brown windings bad news. Gook luck

SOURCE: Craftsman 6hp 150psi 30gal won't keep running

It sounds like the internal circuit breaker in the motor is heating up and then the breaker trips to shut down the motor. This is the protection so you don't have a fire if the motor burns up. The smell you have is the coils in the motor. Sorry to say that you will need a new motor for this unit. I hope this helps out.

SOURCE: Craftsman Compressor runs Intermittantly

I have repaired many craftsman compessors with the problem that you are having. I just use the process of elimination to find the broken wire. I use a short pigtail and attach it to the motor side of the pressure switch. This will isolate the motor from the switch and the power cord. Use caution not to overfill the compressor as this will test the safety valve. If the motor runs ok then move the pigtail to the powercord side of the switch. This will eliminate the power cord. If problem is within the motor check the connectors under plate and capacitor cover. To test the capacitor you will need to find a meter with cap test capabilities or repair shop will test for free. The cap should test within 95% or printed value in (uf). If all parts test ok then motor could have internal thermal breaker that is weak. Good luck.

SOURCE: no air pressure

TRY ADJISTING THE TANK PRESSURE KNOB WHILE RUNNING ,TURN TO THE RIGHT 1/4 TURN UNTILL YOU SEE NEEDLE MOVE .MOST TIMES FACTORY SETS AT 0,SO YOU NEED TO ADJUST IT .MY ADVICE IS NO MORE THAN 90-100 PSI TILL YOU KNOW WHAT YOUR RUNNING MORE OFTEN

SOURCE: Have a Craftsman Professional 150 PSI 25 Gal 1.8

Sounds like one of the following three possibilities:

Too small of service to the unit... You need 20 amp and #12 wiring.

Too long extension cord with too much voltage drop.

The "unloader" is defective. This is a little valve that MAY be a part of the pressure switch that bleeds cylinder head pressure at shutdown to make starting easier. At shutdown you can usually hear it "exhale".

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