Compressor not working

Are you thinning the paint you are putting in the jar?

off the memory - on this particular model you have knob just before the valve and indicator, lift it up and turn clockwise to increase pressure and anticlockwise to decrease it.

indicates the small seals around the needle are hard and not sealing properly

If you can hear air bleeding off through the air filter when you turn it off then the check valve has failed on the compressor discharge to tank line and cannot overcome the tank pressure. If there is no air coming out through the air filter than the intake and dischare valves have become weak or are broken/not seating. Post your findings, I wil see if i can help I worked on compressors for 5+ years

It sounds like you have a dirty tip. It doesn't take much to stop the flow to the tip. You need to take the tip completely apart to give it a proper cleaning. Just soaking it won't do.
Hope this helps but if not let me know and I'll try and trouble shoot further.

could be the capacitor, also try looking at the wires around the windings

Air compressors are designed to operate many different tools. The value of a commercial air compressor is many times greater than the purchase price because of the amount of work a single air compressor can perform. Dental air compressors are some of the most reliable because of the high-quality air they supply and precision tools they operate. As a result, dental air compressors can be adapted for a number of different tasks, including artistic air brush painting
1.Disconnect the air compressor from the dental tool air supply. Pressure and air supply rate-of-flow settings are different for air brush painting than for air delivery for dental tools.
2.Reset the air pressure on the tank to a range between 15 and 20 pounds per square inch (psi). The exact operating pressure for airbrush painting will vary, depending on the application and the type of paint used.
3.Reconnect an air-supply hose and a siphon style airbrush to the compressor.
4.Fill the airbrush's paint vile with lacquer-based paints. Test the air brush and paint performance on a piece of cardboard, or scrap piece of cloth
material before beginning the painting project. Every time the air compressor is connected to airbrush, or a new paint color is loaded into the brush, a short test spray should be performed. After each test adjust the air volume, and the paint flow in the gun to achieve the desired results

1)Let your unit pump up.
2)Turn it off.
3)Find the supply line from the pump to the tank.
4)Remove the supply line from the pump head.
5a)If you hear air coming from the tank you have a bad check valve.
5b)If you do not hear air coming from the tank, you have a leaky
pressure switch.