Dewalt D55168 air compressor runs until 95 psi and never stops. Pressure never goes above 95 psi. It use to stop around 140 psi.

https://www.manualslib.com/manual/494085/Dewalt-D55168.html

Specifncations
MODEL D55168
WEIGHT 88 Ibs. (39.92 kg)
HEIGHT 41.75" (1060.5mm)
WIDTH 19.0" (4826 mm)
LENGTH 21.25 (539.8 ram)
AIRTANK CAPACITY (GALLONS) 15 Gallon (56.8 fiters)
APPROX CUT-_N PRESSURE 160 PSI (1103.2 kPa)
APPROX. CUT-OUT PRESSURE 200 PSI (1379.0 kPa)
SCFM @ 90 PSI (620.5 kPa_ 5._

cant get fixya comment to work so will edit here...

The 200/160 are the typical DS55168 settings from factory and meet the 90 psi @ 5.4 cfm rating.

Pressures can be adjusted to a MAXIMUM 225/185 with a resulting lower cfm rate.

I'm not familiar with "type 9". Likely nothing special just different setting from factory?

http://www.toolpartsdirect.com/makita-mac5200-3-0-hp-air-compressor.html
There is a part called an unloader. It reduces the pressure on the compressor when the unit stops at the desired pressure. The actual unloader may be part of number 50 in this diagram.

You need a new pressure regulator switch.

If you bought it at HD return it for a new one. If not you will need to use a meter and check power from receptacle to on/off switch to pressure switch., Check motor winding. If all else fails call Dewalt and they will help you.

Worn ring and cylinder or bad valves maybe.

Your concern is very well placed, at pressures that high a lot of damage can be caused by a failure. According to the manual for this model air compressor the approximate cut-in pressure is 160 psi and the approximate cut-out pressure is 200 psi. Meaning it should pump up to 'about' 200 psi and shut off and not come on again until it gets down to 'about' 160 psi. They say approximate and I say about because it's not an exact science setting the pressure switch. Spring rates are not always exact, pressure guages are not that precise, etc. When turned on, it should shut off at 200 psi +/- 10 lbs. If it goes more than 10 lbs over that (220psi), I'd recommend you get the pressure switch and or guages checked or replaced.

The regulator switch/unloader is bad or out of adjustment. Perhaps though the gauge is faulty. 200 psi in a 120psi compressor is dangerous, don't run it until it is fixed!

Here is a parts diagram for the air compressor:

http://shoppingcart.msservicecompany.com/msservice_net/product_files/D55168/D55168_PL.pdf

 

There are a couple of things to look for on the air compressor.

You will need to see if the piston ring is damaged or if you have a broken reed on the valve plate.

 

These are typically the two most common problems with this model.

 

You suspect this unit as being a two stage because of the unusually high cut off pressure. It is a single stage and the motor really has a difficult task and is being pushed to the limits. to reach this pressure. We usually reset the pressure to lower setting ~~ say around 140. Your pump probably has a leaking intank check valve (brass fitting at tank) or leaking valve plate in pump. Simple tests : with pressure in tank unplug compressor from outlet and listens for air leak around pressure switch. As you unplug the running compressor from outlet you should hear air leaking from pressure switch for just a moment as air is let out of airline from pump to tank. If air leaks out till zero pressure then change the valve. If tank holds pressure then valve probably ok. Next test, with no air in tank and air filter removed, plug in compressor and feel intake port for strong suction. If the valve plate is bad, suction will decrease as pressure neers the 120 mark till the point of feeling that air is actually blowing out of intake. With good valve plate there will be strong suction untill unit reaches set pressure. If valve plate is bad also change the cylinder and piston ring. Good luck with your repair.

Hi there. This is normal. The pressure is set to stop at around 120-140 PSI as a safety measure. It probably kicks in again around 80 PSI so as to remain pressurized between 80 and 140 PSI. Since most air tools operate in this range, it is ok for the compressor to maintain pressure in that range. You do not want to adjust the maximum pressure safety release valve as it could be extremely dangerous as certain components in the compressor may only be rated up to 140 PSI or slightly higher before they fail or blow apart.