N14 slow building air

[crane operator]

1998 N14 in a t800 cummins. New to us truck that we stretched a little frame, added axles and a flatbed to haul counterweight.

Truck never built air well when we got it. This is one of the last things we've dove into to fix. Started with air dryer and governor. Next went to reman air compressor. Have replaced lines between compressor and dryer, and also tested it with dryer bypassed and just pushing air straight to the tanks. (In case the new dryer was plugged/ issues)

New compressor can almost hold your thumb on air output. Will build air slowly towards 60, then requires throttle to get to 90, and a lot of time at rpms to get to 125.

If you get it to 125 and pump the brakes down to 90, its 3 minutes at 1500rpm to get back up to 125. Which in all my other trucks you can just watch the gauge climb back up that amount.

So I was wanting to tear into the unloader valve on the new reman, but Inland didn't want me to do that, so they just got me another reman. We've got the new reman mounted now, and I was just wanting to double check my young guy, and had him pop loose the coolant lines.

There was water at the coolant lines when he changed the compressor, but there's no water flow at idle to the compressor. Shouldn't we have coolant flow at the compressor- even if the thermostat isn't open yet?

Junkyard suggested I check the intake air line and make sure it isn't plugged, which is possible. I hadn't thought of that one. Also, he suggested a quick valve leaking out, which I haven't heard, but my hearing isn't great. I was thinking to check that with shop air, and then disconnecting the shop air and see if the truck gauges hold, that should show me if I have a bad enough leak that the compressor just can't keep up.

I do have a pretty high volume demand on first start up- its a 8 bag KW suspension and there's 4 more lift bags to push the extra axles off the ground also. Which could explain the long initial volume time, but not the struggle from 90-125.

I'm all ears for any other suggestions.

 

[Truck Shop]

Is this a single cylinder cummins compressor? agree with JY inlet air, your idea of pressurizing
system with shop air is a good one, but do it right off the compressor discharge line and time
it to 125 psi. Should be a coolant line from left front of block and left center of block, those
normally circulate at a slow rate till stat opens.

 

[crane operator]

Junkyard put me on the right path he brought up checking the fan clutch. And it ended up being in that system.

My young mechanic turned the key on when testing some other things, and Pssssttt. Air leaking from the fan clutch solenoid. With truck running, couldn't hear it leak. Shut the engine off, to listen for leaks, no leak. Shop air to it, with no key on it- no leak. Testing with key on, not running, was the trick.

Turns out someone had replaced the fan clutch solenoid- who knows how long ago- and actually had the solenoid plumbed incorrectly. Would dump air constantly, and I don't know how anyone could drive it like that.

Anyways, just wanted to update what the problem was. Thanks truckshop and junkyard for the help.