Low air pressure while driving on freeway!?

The compressor is always "on", it just goes into loaded and unloaded states. So, there'll be a hose typically from one of the tanks to the air governor. When the pressure in that line reaches cut out pressure (115 - 130 PSI), it opens up a valve in the air governor and sends air through the two outlet hoses. One goes to your air dryer to close the air dryer outlet and start the purge cycle, and the other goes to the unloading valve on your compressor. For your compressor to be in an unloaded state and not sending air to your dryer and tanks, that line from the governor to the compressor has to be charged. It's possible your governor got hung up. Cut out pressure is supposed to be no more than 25 psi below cut in pressure, so if it's cutting out at 120 and cutting in at 95, you're still good. That one, if you wanted to throw a part at it to err on the side of caution, an air governor isn't expensive at all.

Was it your primary or secondary system which dropped below 75? And what were the conditions it happened under? Were you doing a lot of braking, was it a rough road bouncing you up and down a lot, etc.?

 

You can bypass it all together with the right fittings.As long as you’re in warm weather.

 

Geez $750 to change out the air dryer, I changed mine out for $100.00 after market dryer though.

 

Fleetpride brand new AD9 $150

 

Purge valve and cartridge are. Governor is not but still very expensive.
Try to do it yourself if you can and save yourself about $500.

 

$150 is a good price for a new unit.