jasonemryss Posted July 12, 2017 Share Posted July 12, 2017 I just bought a 99 Mack ch13 that I knew had a couple issues but didn't let phase me. But for the life of me, I can't figure out why the compressor won't stop building air. The check valve on the compressor releases & that keeps the pressure around 120psi. I've replaced & athe governorll the valves from the air dryer back. I'm get this truck road Worthy. Any suggestions? Quote Link to comment Share on other sites More sharing options...
thomastractorsvc Posted July 16, 2017 Share Posted July 16, 2017 My guess is an issue with govonor or the way the lines are hooked up. The governor is what controls the air build up and release of the compressor Quote Robert"I reject your reality and substitute my own." Link to comment Share on other sites More sharing options...
turckster Posted July 29, 2017 Share Posted July 29, 2017 If the governor is plumbed correctly the unloader valve may be stuck in the air compressor head or the wet tank/signal line could be plugged. The air governor has 3 ports-unloader, exhaust and reservoir. The reservoir port goes to the wet tank, the unloader goes to the air compressor unloader and the air dryer purge port, exhaust is open. The air governor gets its signal from the wet tank. Once the pressure in the wet tank reaches 125-130 psi the air gov. sends an air signal to the air compressor unloader and dryer purge port. Once the air pressure drops a certain point in the wet tank, the air gov. dumps the unloader signal and allows the air compressor to build air pressure. When I am diagnosing purge issues i install a gauge into the unloader port and a gauge into the reservoir port on the air governor, that way you can see what the air pressure is in the wet tank and what the air gov. unloader pressure is (should be same as system pressure). If everything looks ok, make sure the air lines to the air compressor and purge valve are not plugged and will hold pressure. If all looks ok there as well then the issue most likely is the air compressor unloader valve being stuck. Quote Link to comment Share on other sites More sharing options...
Underdog Posted July 29, 2017 Share Posted July 29, 2017 Signal line may be plugged or have a pinhole.Sent from my XT1254 using Tapatalk Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted July 31, 2017 Share Posted July 31, 2017 On 7/29/2017 at 0:11 AM, turckster said: If the governor is plumbed correctly the unloader valve may be stuck in the air compressor head or the wet tank/signal line could be plugged. The air governor has 3 ports-unloader, exhaust and reservoir. The reservoir port goes to the wet tank, the unloader goes to the air compressor unloader and the air dryer purge port, exhaust is open. The air governor gets its signal from the wet tank. Once the pressure in the wet tank reaches 125-130 psi the air gov. sends an air signal to the air compressor unloader and dryer purge port. Once the air pressure drops a certain point in the wet tank, the air gov. dumps the unloader signal and allows the air compressor to build air pressure. When I am diagnosing purge issues i install a gauge into the unloader port and a gauge into the reservoir port on the air governor, that way you can see what the air pressure is in the wet tank and what the air gov. unloader pressure is (should be same as system pressure). If everything looks ok, make sure the air lines to the air compressor and purge valve are not plugged and will hold pressure. If all looks ok there as well then the issue most likely is the air compressor unloader valve being stuck. I was performing this diagnostic last month for a truck that would pop the air dryer purge open and continue to chatter compressed air out of the bottom of air dryer purge valve. The new air governor was only letting about 30 PSI into the unloading circuit. It was enough to open the air dryer purge, but not unload the sprung unloader stems in the compressor head. Warrantied reman air governor and bought a new instead of reman, problem fixed. New part fails are hard to diagnose, it throws a tough variable and makes you second guess yourself. I put a gauge in the wet tank too. Pop out the safety valve and an 1/8" pipe nipple gauge slides right in. Quote Link to comment Share on other sites More sharing options...
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