2003 Freightliner Columbia Air Pressure Regulator

Its located on the driverside of the engine its on the back of the air compressor. If it has a blue cap its not adjustable and was factory set if it has a black cap its adjustable. It costs about $48.00. You could replace a non adjustable if you would like to

 

Also after time the spring in the gages become weak and will not give an accurate reading

 

Ok what kind of engine. I'm not near my truck right now to take a picture for you.once u tell me ur engine I will find a picture for you. If you private message me with your phone number I will call you and walk you through it

 

Ok let me see if I can find a picture for you

 

picture of the air governor. This is an adjustable one as you can see the black cap.
http://m.ebay.com/itm/161050045073?nav=SEARCH&sbk=1

 

Does your air dryer look like this?


If so, the grey "tube" on the left with the blue cap is the regulator. Blue cap is non-adjustable and preset at factory at 135psi. If it has a black cap, it can be removed and adjusted, there should be a lock nut and adjustment screw.