[flananuts]

I just finished putting Arnott Gen III air springs all the way around on my P38. I have manual schraeder valves and a tank pressure gauge on my setup. I dropped the truck to it's lowest setting before manually airing down the springs and replacing all the bags. I also manually aired the bags up before starting the truck. MY EAS compressor, which is rebuilt, isn't turning on and building pressure back up in the tank. Occasionally the compressor will come on but only for a short amount of time and the tank pressure has yet to go past 80psi.

I failed to disable the EAS while having the truck jacked up over night, but there aren't any faults to clear. I'd like to get this truck back on the road. What am I missing?

Thanks

Matthew

 

[annette]

check the compressor temperature switch. Bypass it and see whether it works

 

[NorCal RR]

By bypass, you mean ground it correct? There are thermal cutout and pressure switch diagnostic methods in the Repair Details section of this site. I would assume that intermittent operation means your fuses and relays are all good.

 

[flananuts]

Thanks for the thoughts. I find it hard to believe that temperature or pressure related switches are the culprit however once the bomb cyclone on the east coast leaves us I will check that. The valve block and compressor are very recently rebuilt and were working prerfectly as designed, with the compressor kicking on when tank pressure was below maybe 120 and shuts off at around 145-150 according to my gauge. The brain works because when I tell it to go to ride height the back end rises up but the front isn’t because the tank pressure is at 60. When fooling with the ride heights settings using an EAS kicker the compressor would turn on but seems to be stopping at 80psi. I’m also wondering if I should just disconnect the battery for 5-10 minutes and then reconnect.

 

[Richard_G]

I’m also wondering if I should just disconnect the battery for 5-10 minutes and then reconnect.

All that will do is cause you to have to reset the windows, sunroof and reprogram the radio. Disconnecting the battery on a P38 does not reset any of the ECU's. If the pump does run some of the time it isn't the thermal switch that has failed (although if the pump is getting too hot it may be cutting out as designed although that usually takes 15-20 minutes of running). That only leaves a problem with the pressure switch although why it would fail immediately after you changed the air springs seems to be a bit of a coincidence.

 

[flananuts]

Thanks Richard. It appears that could be the case. The pump will turn on and pump up to 80psi but not any further. I didn't disconnect the battery lol. Is there anyway to override the pressure switch or test it? I hate swapping parts for the sake of swapping. I should also add that there are no fault codes either.

 

[flananuts]

Update: I used my multimeter to look for resistance on the pressure switch. I tested pins 7 to 9 and looked for the ohm reading to go from 1 to 0 and manually ran the compressor up to 130. There wasn't any change on the pressure switch reading when above 120psi. Does this sound like a pressure switch issue?

 

[NorCal RR]

Are you following the diagnostic I mentioned? It should be an open circuit if you are measuring these pins on the correct plug. It may seem unlikely to you but there isn't much to cause the compressor not to start if its getting voltage and operational.

If the pressure switch in the EAS valve block is faulty, it can tell the ECU that no pumping is needed when it is. To check this out, you can unplug multiplug C152 from the valveblock drivers (see photo at top of page for its location) and test the resistance between terminals 7 and 9 on the valve block side of the plug; an open circuit should be noted if the sustem pressure is below 8.5 Bar (120 psi). Or, check pin 13 on the Air Suspension ECU under the left front seat -- if it shows +12 volts the pressure switch is closed, indicating that it thinks 150 psi has been reached.

 

[flananuts]

Thanks. So I suspect the pressure switch is the issue but here’s what recently happened. My brother broke down in my Defender 110 on the highway late Sunday night. I manually inflated the tank using the jumper. While driving when the truck lowered to hwy and then when stopped it raised back up and the compressor kicked in and pumped up to about 145psi. So I think the pressure switch is working now that the tank pressure is up to normal operating pressure. I will also be able to test pins 7&9 as well to confirm that the switch was the culprit. Appreciate the input.

 

[flananuts]

Update. I tested thermal switch when cold and I got no resistance. I manually bypassed the EAS and used a jumper to pump the compressor up above 140. I tested pins 7 and 9 below 120 and above 140 and my meter read open circuit all the times. On a separate occasion I bled the tank down to 60 and started the car. The compressor turned on and pumped up to 80psi and then shut off. Before I pull the block out and replace the pressure switch is there anything I can test on the EAS ECU under the front seat?

 

[flananuts]

Closing out this thread. I was able to put enough pressure to get the pressure switch to show continuity and finally got my thermal cutoff switch to show faulty. Appreciate all the suggestions on this.