The gun constantly exhausts air when connected to air compressor. Won't build up the pressure when connected. Must disconnect between firing trigger

possible --also crank--piston --gasket failure

you may have to rebuild it again. inspect nail gun piston cylinder to ensure that it is not worn or scratched. Is the gun lubed before each use and periodically under heavy use?. Water from compressed air will damage gun.Use quality parts use buna n o rings not buna o rings
good luck

https://www.ereplacementparts.com/repair-center/article/7451/How_to_Install_an_Overhaul_Kit_in_a_Porter_Cable_Nail_Gun.html

Replace the O rings... sounds like its one in the firing valve ( rear cap of the gun behind the cylinder )

Hi

Here are a few things to check, you may have already checked some of these.

*Electricity...Compressors will run best with full 115Vot 15AMP/Or 220V electrical supply from a circuit, over the shortest electrical cord as possible.

*Air Leaks..Place your ear close to the compressor and listen for air leaking, if you hear air that is not normal and means you have to locate and repair whatever it is that is leaking.
*Check the air unloader valve... The air unloader valve will blown out air when you turned off the compressor, that is normal.
But it should not have air leaking out of it all of the time. If so then it is faulty and in need of repair/replacement.
*Valves...If either the intake or exaust valves fail, breaks, or fails to seat, then your compressor will run 24 hours a day and never build up to the correct pressure for shut-off.
*Gaskets...Check to see if your gaskets have failed.
You could have a gasket failure between the pistons and you will never know it because it shows no external air leak.
If this situation happens then the air will only cycle between cylinders and never build up the correct air pressure.
One way to check the gasket is remove the air filter, then put your hand over the intake.
If correct then it will **** you hand against the intake.
If the valve or valves have failed then you will feel the air sucking in and blowing out.
*Piston Rings and Cylinder...The piston rings could be stuck,broken, or worn and not allowing the correct pressure to build up in your tank.
A worn cylinder will also contribute to the problem of pressure build-up.
*Pressure Switch...Check for air leaks at the pressure switch, it has a rubber diaphram that can fail and leak air out of the system.
Please take time to rate me
Bud

It sounds like your pressure switch is not set correctly. It is possible it is set too high for the compressor you have.

No there is not a filter. Since the pump is enclosed in the plastic covers there would not be a way to service it. Now if it is not building any pressure then it could be a few things. First would be the drive belt. (item 125) If it breaks then it won't pump at all. Also if the air hose that exits the pump (item 122) gets a hole in it then it won't fill the tank. A worn head valve plate (item 106), blown gasket (item 105), or a worn piston and sleeve (items 109 and 112-2) can also cause this. If the check valve into the tank (item 16) gets stuck open it too will limit how much the compressor will pump BUT usually it will build up some pressure then just keep running without building any higher pressure into the tank.

Here is a parts diagram so you can see where the belt and other parts are located plus it contains all of the part numbers.

PC CF2600 diagram

Either the pressure switch needs adjusted or the compressor needs rebuilt.

The simple answer is, Yes, but not as well as a larger unit.

2 gallons is small to begin with u need to buy an in line pressure adjuster/regulator their a few bucks and can be attached to the paint gun or line and will keep the pressure at ur adjustment the regulator on the tank sets the tank pressure at 50 so when u us it will let it drop down to about 45 than start up to build the pressure up to 50 than shuts off than repeats it self the inline keeps pressure steady even if tanks are at 200 psi

I assume it keeps pumping, but doesn't build any more pressure. That is probably bad valves or rings. If your unit has a crankcase breather, and it is puffing alot of air, look for rings. Otherwise valves.