Porter Cable's line of air compressors are designed to help with home and shop projects. They are not immune from problems, however, including air leaks, motor problems and excessive air pressure build-up. There are some simple solutions to basic problems, though some problems may require professional repair.
Turn the compressor off and allow the motor to cool if the compressor suddenly stops in the middle of operation. This is likely a sign that the motor overload protector has triggered due to overheating. Once the motor is cooled down enough, the compressor automatically restarts.
Unplug the compressor from the current electrical socket if the motor does not run and plug it in to another, if one is available. The current one may not be providing enough power to the compressor. If you are using an extension cord, unplug the compressor from the cord and use a different cord (or plug it in to a wall socket, if one is available). Check your home's fuse box for a blown fuse and replace the fuse if it is blown. If your home's circuit breaker has tripped, reset the circuit breaker.
Set the on/off lever to the "off" position if the safety valve pops off. This is a sign of excess build-up in the tank due to the pressure switch failing to shut the motor off when the pressure reaches cut-out pressure. Cut-out pressure is higher than the highest allowable pressure in the the tank; the switch shuts off the motor for safety reasons. Have the compressor professionally repaired.
Check the fittings for air leaks if you notice weak air output. If you can hear air leaking at one of the fittings, tighten the fitting to stop the leak. Check the safety valve for air leaks. If air is leaking, pull on the safety valve's ring. If this fails to stop the leak, the valve is defective and must be replaced. Check for air leaks between the head and valve plate. If air is leaking, you need to have the compressor professionally repaired. Check for air leaks at the regulator knob. If there are any, the compressor has a bad regulator and must be replaced.
Decrease the amount of air you are using if the air output is weak. Using too much air over a prolonged period can cause output to weaken. Check your air hose for leaks. Check the air requirements for your tools (printed on the tool or in a manual) as well as the recommended air output of your compressor. If the air requirement for the tools is higher than what the compressor is capable of producing, the compressor is too small.