low air pressure

Repost to "Trucks [ Eighteen Wheelers ]", this area is for information about the forum itself.

 

any sound of compressor cut off (unloader) and noise of air driyer purge?

 

The governor is probably frozen.

 

yep, i think the same. i'd spill some hot water on governor and I'd change air driyer cartridge and put some spirit ore anty freeze fluid for air systems

 

look at air comp. 1st , drier 2ed. air gov. is round with black end.

 

The OP was asking where the governor is, baha. Describing it doesn't answer his question.

The governor is typically mounted right alongside your air compressor. Usually small round/cylindrical shape, as baha said.

Governnor may have a black cap, as in the first Cat pic, or may have a painted or plastic cap as in the 2nd Freightliner pic.
In 2nd pic... Red arrow points to compressor, Yellow arrow points to governor.

 

If you are not building pressure over 50-60 pounds, you are probably losing air somewhere. If it is your air governor, you can sometimes feel air leaking out of the back. Sometimes it is difficult to hear air leaking from the governor. It would be the least expensive thing to replace. The air dryer is another possibility. If it is remaining open then you won't build air. Sometimes a little grit or dirt can prevent the valve from completely closing, so it won't build air. Try sticking your hand underneath the dryer and see if you can feel air leaking. One easy way to check your air dryer is to disconnect the air hoses from the dryer and connect them together. If the air still fails to build, it is not likely your air dryer. If it does build once the hoses are connected, you might try replacing the dryer. Another potential problem is the pressure relief valve, sometimes called the pop off valve. It is located on the side of your air compressor. Once they pop open, they need to be replaced. The valve is usually easy to spot and looks like it is made from brass. At least you are building some air, so it is not likely your compressor. One other thing. Most trucks have pressure release valves on air tanks. You may want to check all of them to make sure they are not leaking. Again, a little dirt can prevent the valve from closing completely. I would put my money on the air governor or air dryer.