2017 Mack Granite - Absurdly High Air Pressure - 150+ PSI

Question

My 2017 Granite is overcharging the air system. The secondary and primary gauges go all the way up to 150-160 psi and then the safety blow-off valve on the wet tank pops. It sounds like a gunshot.

I replaced the air governor on the compressor and it did the same thing five minutes later. I then replaced the entire air dryer assembly (AD-IS type) thinking the internal purge valve or check valve was stuck. Still overcharging.

WeldShopWanda · Accepted Answer

✅ Confirmed fix: The unloader pistons inside the air compressor head were carboned up and stuck in the 'closed' position. Even though the governor was sending air to unload them, the pistons wouldn't move. Pulled the compressor head, cleaned the carbon, and replaced the unloader kit. Back to 125psi cut-out.

NoStartNoel · Answer

Check the signal line from the governor to the compressor unloader head. If that line is blocked or leaking, the compressor never gets the signal to stop pumping.

2017 Mack Granite - Absurdly High Air Pressure - 150+ PSI

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