M939 Air system Diagnostics - No air pressure/low building pressure

Рет қаралды 16,443

5 жыл бұрын

This is a diagnostic procedure of when your truck will not build any air pressure at all. OR will not build air pressure above a certain PSI - like 40 or 60psi.
This is where you start. Add your gauge to the compressor first to see what the output is. Low pressure indicates a unloader or compressor problem. If it is pegging the gauge out then you know you have to move down the discharge line to find out where you are dropping the pressure at.

Пікірлер: 13

@clementemendez357 4 жыл бұрын

Could you make a vid cleaning out the unloader valve, that would be really helpful. I have not been able to find anything on that. This vid was tge most helpful I've seen so far. Good vid

@williampierce5615 2 жыл бұрын

Thanks. I will use your knowledge and fix a vehicle tomorrow. Thank you.

@BD-qq4fn 3 жыл бұрын

Great video!

@garygeer7646 3 жыл бұрын

😎👌

@waltgoebel8814 4 жыл бұрын

how do you get the unloader unstuck?

@wessimpson2794 4 жыл бұрын

Remove the head and unloader. Clean it and lube everything up then reinstall

@williamrekow7513 2 жыл бұрын

Would be nice if the video pointed out what an unloader is, and what you mean to do with it.

@wessimpson2794 2 жыл бұрын

Unloaded is the top of the compressor separate from the cylinder head that is held down by 2 bolts.

@joytrucker5709 2 жыл бұрын

I have a cummins ISX15 I want to test the air compressor. Any chance they sell a gauge I can buy or do I have to build it like you did? Do you know how I can build one?

@wessimpson2794 2 жыл бұрын

You can use a air pressure regulator like for a shop compressor from home depot Or just get the gauge of they sell it. Install a bushing on the back and rig up your air fitting etc. You can use hydraulic line or air line

@joytrucker5709 2 жыл бұрын

@@wessimpson2794 Man I really wish you made a video on how to make one.

@joytrucker5709 2 жыл бұрын

@@wessimpson2794 Today I went to Lowes and bought a gauge. Tried to find a fitting that would fit the compressor and reduce it down to a 3/8" hose that connects to the gauge but could not find any. Do you know if the compressor uses a NPTF? The closes thing I found was a garden hose type that partially fits. Where is a good place to buy fittings for a semi truck air brake system. I tried Lowes, Home Depot, Ace, Harbor Freight. None have the right fitting.

@joytrucker5709 2 жыл бұрын

@@wessimpson2794 It was a mission but I did it. After going to every hardware store in town I went to Peterbilt which didn't have it either, but the man there directed me to a local place called ABC Hydraulics. It was there that I found every possible bushing and fitting imaginable in stock. It all worked flawlessly without any leaks. The gauge moved violently between 120 and 180 PSI. I'm so happy I got to test my air compressor and it's working fine. Worth Noting: I first bought a fancy liquid filled gauge rated for 200 PSI for $15 at Lowes, but when using it the needle shot past the max and never came back down. Thinking it was broke, I then went to Walmart and bought a cheap air gauge rated for 300 PSI for $5. It worked just like in your video. Altogether with the gauge, bushings, and fittings, I spent about $50 plus my time and labor.