M1078A1P2 Air Dryer

[Mxpert]

Truck will not purge air from air dryer, builds up 120 psi in front and rear tanks. After shutting off truck it will release air from quick release valves. Any one run into this problem some assistance would be appreciated. Thanks

 

[Mxpert]

Sorry forgot to mention it has the new style air dryer. No fins. Air Dryer filter has been recently changed.

 

[NDT]

Is the system over pressurizing? If so the lack of purge is an issue with the compressor unloader. If you have over pressurization, the relief valve will burp. If this is not the case, the dryer sneeze valve needs some love.

 

[Ronmar]

When you say QR valves what exactly are you referring to?

When the air system reaches set pressure the governor/unloader on the compressor unloads the compressor and sends system air pressure down a small control line. That line runs to the purge valve control port on the dryer.

If you are not purging my first check would be that control air is coming down that line when the compressor reaches cutoff. Be careful and keep the line under control/restrained when removed as it will have 120 psi exiting it when the governor unloads. If that control air pressure appears on the dryer purge line, then the purge valve is the issue and needs service/repair.

If the air isn’t on that line, either the governor is unloading and not sending it, or it is never reaching set air pressure and unloading. Remember the governor senses air at the wet tank so leaks, clogged dryer or failing compressor could cause the air pressure at the wet tank to not reach cutoff pressure…