Thank you for your question.
Your air compressor probably has something broken inside the cylinder. Disconnect the power to the air compressor and remove the plastic cover around the motor and compressor.
Before you take the compressor apart, listen and feel for air leaks. Check to see if air is coming back out of the intake filter. If air is coming back out of the intake filter, the tank check valve is the problem. If you feel air coming out of the intake when it is running I suspect the valve plate is broken.
I recommend checking the tubing connections to the pump. If the connections are fine, you have to remove the head. The head is secured with four bolts. Directly under the head is the pressure plate. The pressure plate has reeds on it that direct the air into the discharge line and keep the air from going back into the cylinder of the compressor. Check the reeds for warping or breaking. If the reeds are damaged, you must replace the pressure plate. Make note of how the pressure and seal sit on top of the cylinder.
If the pressure plate looks fine, I recommend setting it aside and inspect the piston and the cylinder. What usually happens is the piston ring wears and allows air to blow past the piston. When this happen the compressor will run longer and may never come up to full pressure. To repair this problem I recommend replacing the piston ring and the cylinder. Most compressors have a kit available that contains the piston, ring, cylinder, and the seals.
Please feel free to reply with more details if you need further assistance on the repair of the compressor.
If you do not feel confident repairing this problem yourself, then you can have it repaired by a Sears technician. Here is a link that will provide the nearest drop-off locations:
Sears Home Services
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