I bought a Dewalt D55168 air compressor and I lost its owner's manual. Where can I get or download it, please?

you may be using more air that unit can supply. This is a very common error. it is only 5 cfm which is small.
Call Whitton Supply Co. or visit our local Oklahoma City showroom (405) 236-5561.

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?

Valve plate

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.

Check for leaks all over the machine. Possibly the O ring on the drain valve is damaged. If the machine is oil-less, the big rubber O ring on the piston could be worn away.
When the machine is turned off can you hear air leaking from anywhere?

http://www.factoryauthorizedoutlet.com/DeWALT/Products/D55168.asp

You can order one here.

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.

 

Here's a link to a diagram of your compressor. I couldn't tell much by looking at it but maybe it will be of some help since you can look at the diagram and compressor. Part number 37 is the filter. Good luck!

http://www.dewaltservicenet.com/Products/DocumentViewPDF.aspx?productid=66646&typeId=15502&documentId=34640

The dewalt model d55168 is a high-end oil-free compressor. Oil free compressors could have a short life span due to dusty or dirty conditions at the job site. The cylinder of your compressor is open from the bottom and will **** in debris scratching the cylinder/ silicone-vinyl piston ring reducing pressure. However the reduction in pressure will be over time till the point that the compressor will not reach cut-out pressure and just keep running. If you lost pressure suddenly to "0" then you probably lost the drive belt. A replacement can be found at a local dewalt service center or ordered thru www.toolpartsdirect.com. When you take down the compressor, be sure to examine the cylinder /piston for wear. These are the two most common problems. Good Luck on your repair and email if you have other questions.