air dryer
- Thread starter rich204
- Start date
Truck Shop
Well-known member
That and the cartridge is full of oil and moisture. The purge valve is probably wore out too. A tired D-2 Governor will also cause cycling. Air dryers should
be serviced at least once a year, depending on climate. Servicing them just before winter is the best. What type is it AD-9, AD-IS or AD-IP? The IS has a
6" dia spin-on cartridge, IP is a 9" with a draw bolt that has a 5/8 head that is installed from the bottom up. The AD-9 has 8-3/8 bolts holding the top cover
on with the cartridge inside. All of these are easy to service.
Truck Shop
Most likely your air compressor is not unloading and is building continuously. Once purge occurs your air pressure should drop to 90-100 with air consumption and then build back to cutout pressure-120-130. If your governor has two air lines you need to check the reservoir line for tank pressure and or leaks. We know the unloader line is good as the dryer is purging. Likely that you have an unloader valve hanging up in the compressor. ID'ing the compressor and dryer can help narrow things down. I agree with servicing the drier also as suggested previous.
Truck Shop
Well-known member
Good point about possible unloader issues also. Glad there is someone adding info on this forum.
Truck Shop
Truck Shop
Last edited:
Truck Shop
Well-known member
Come on now you stand lots of chances 
Truck Shop
Truck Shop
the other thing to check is a leak in the wet tank before the primary or secondary tanks, because the wet tank is not gaged. the purge valve needs a signal from the compressor cut out circuit to pop off, so the compressor has to be cycling on and off to create a rapid purge action, the purge air is just the air between the compressor outlet and the check valve on the outlet of the dryer.