Question about Craftsman Air Tools & Compressors

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My 1 hp. 12 gal. air compressor is not building air pressure the motor runs the pressure won't go above 20 lb.

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It could be that the input air filter is badly clogged. I might more likely be that the Non-return valve on the air tank input is not sealing properly and not allowing the tank to build up pressure. This valve is at the end of the main pipe runs between the compressor and tank. It could also mean (less likely) that the poppet valves inside the compressor cylinder head are not sealing properly. Other faults could be worn rings on the compressor pistons or a bad seal between the compressor cylinder head and block.

To check the Non return valve allow compressor to build up some pressure and then loosen union nut on Non return valve. There should be some air released at first but should stop if valve is ok. If leaking remove valve and check for dirt and clean. If valve still leaks replacement is the only fix.

Posted on Sep 15, 2010

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1 Answer

Will only build air to 35 lb .keeps running but no air above 35lb


Most likely it is a leaking valve. If ether the intake or exhaust valve, but not both, leak back pressure will be low. These small compressors usually use reed valves. Try and remove the head, and check that the reeds are not bent up, and that the seat it seals against is not cut. If the reads are bent you can sometimes flip them over. You may be able to get new reads from Sears if they are bent or broken.

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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.

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Very hot air is an indication of leaking /broken head gasket or reed valve. Before you remove any parts, with compressor running, check all fittings for leaks with soapy water. If no leaks, remove head and examine parts. If reed valve is broken replace as needed or do creative repair. Some valve plates have multiple reeds and only one reed is broken. Depending on your skill level, you can thread the hole and seal with piece of bolt (finished repair must not be any thicker than the plate). Good luck

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I HAVE A CRAFTSMAN 1 HP 12 GAL AIR COMPRESSOR THAT WILL ONLY BUILD 20 PSI THE COMPRESSOR ONLY HAS 1.5 HRS RUN TIME ANY SUGESTIONS


hi there, if the compressor built up a 20 psig and run at 1.5 hrs.then stop.check the pressure switch the differential pressure cut in and cut out limit.adjust the cut out to the corresponding cut out pressure you want but not exceed to the designed pressure tank..this will be done on adjusting cut out pressure screw mounted inside the pressure switch.follow the instruction on the manuals adjusting pressure switch.the run time correspond to the cut out limit of the pressure switch. rate my fix if your satisfied thank a lot.

Apr 20, 2010 | Air Tools & Compressors

1 Answer

No air pressure


If your motor is running and the pressure is not building it is either the valve plate or the compression ring. Check both for damage.

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WILL NOT BUILD UP AIR PRESSURE PAST 20 LBS.


Check to see if air is leaking past 'pressure relief' valve. It's probably leaking and that's where all the air is going.

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Have 12 gallon / 1HP Craftsman compressor, accidentally ran it while it was low on oil....about half way low. It shut itself off. Then, I added oil and it started up. But now it builds pressure VERY slowly...


Not the motor, but probably the compressor shot. Heat from friction (due to running without oil) probably scored the cylinder walls, which allows air to escape past the piston and rings, making the compressor VERY inefficient. Some compressors have replaceable cylinders... Not sure if the very small ones do or not.

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