Replaced air compressor on N14 now same problems again

Ok so last Thursday my air compressor (1.5 years old) stopped building air at a idle so I figured the air gov. had gone bad so I replaced that, took apart the unloader valve and cleaned it up and the compressor still did not want to build air pressure at idle but if I rev(1500-2000rpms) the engine it would build up to around 90psi. So at that point I was only 75 miles to the house I headed home stop by local shop and mech pulled the discharge line off and at a idle he could put his finger over the discharge port and it would not blow it off no pressure.. So we replaced the air compressor over the weekend and it would build pressure but slower then I think it should build at.Which brings my to today...

I left the house at 645 this morning and everything was fine compressor was building air but slow nothing new about that head out on a 4 hr trip to pick up load, as i'm driving i notice the green front tank needle bleeding off air between 90-120psi( I have had this problem here since I got this truck). 3 hrs into trip i stop for fuel and I hear air pissing out so I killed the engine and start to look. come to find out the one thing I didn't replace or look over just broke.. the main discharge line from the air compressor.I get to A KW dealer and get it replaced but it's still building air slowly but now at least its holding pressure. then I notice going down the road if i used the brakes the compressor would not build air until it got down to 100psi, then it would build up to 120-125psi and cut out like it should.

Now here I am tonight with the (new) air compressor not building air at a idle ( pulled discharge line and placed thumb over discharge very little pressure at idle), but I manage get up enough air to release the brakes. I get back out onto the road and air starts to build up past 90psi (55mph). I get the truck out onto the interstate and up to 65mph about 1500 rpms and the compressor would build up to 120-125psi... Anybody have a clue?
 
It sounds like a couple things, two separate problems.

The air building slowly tells me the new compressor is not so good. I assume it is rebuilt. It could be the piston rings were damaged upon installation, or that the cylinder has damage that was overlooked. Just because you have a "new" compressor doesn't mean you have a good one. Most rebuilt parts are coming from overseas now, and I don't think I need to explain how that can affect quality of rebuilt components.

The other issue you might have is another air leak somewhere. You mention the discharge line was broken. You don't say what year, make and model you have, but having an N-14 is a clue that you have an (older) truck. Really check the system over and look for cracked hoses, and leaks at all the usual places, i.e. fittings and connections, diaphragms where the aircan clamps are.

Good luck!
 
Sorry about that Racer X my truck is a 1997 w900l n14 525 with the single cylinder air compressor with the unloading valve mounted to the side of the head on the compressor. The only air leak I have been able to find is on the front tank on the jumper line between the wet tank and front tank there is a check valve there that has a small leak, but other then that i don't hear any air leaking when truck is shut down. Also I have noticed the air intake line for the compressor is getting really hot like the discharge line is suppose to even at idle while the discharge line is cold. right now as i'm typing this i'm waiting for road service to show up since my truck wont build more then 40psi.
 
Sorry about that Racer X my truck is a 1997 w900l n14 525 with the single cylinder air compressor with the unloading valve mounted to the side of the head on the compressor. The only air leak I have been able to find is on the front tank on the jumper line between the wet tank and front tank there is a check valve there that has a small leak, but other then that i don't hear any air leaking when truck is shut down. Also I have noticed the air intake line for the compressor is getting really hot like the discharge line is suppose to even at idle while the discharge line is cold. right now as i'm typing this i'm waiting for road service to show up since my truck wont build more then 40psi.

It's cool.

Sometimes you have to look for air leaks while the air is completely full and the brakes are released. Block the wheels (with the truck on level ground), put the rig in gear and release the brake. If the system won't stay charged while the brakes are released with the engine is off, plumb a air line quick disconnect into the wet tank, and hook up shop air to it. Look for air leaks around the brake cans. They sometimes will leak pretty good where the clamp with a bolt is. If you find a leak, tighten the clamp a bit at a time until the leak stops.
 
Well $1045 later she building air like a champ now..I could have saved a couple hundred dollars if I would have put the correct spring back into the unloader valve before dropping the old girl off at the dealer last night..Oh well they print more money every day right..lets hope the compressor last more then 1.5 years...
 
I was assigned to MWSS-173 '90-'93 in MCAGCC, I was 5811 so when not deployed I was fap'ed over to HQBN
 
One time I was in TN unloading. it was just getting dark. a driver with an ole mechanical cummins had his hood open & said his tuck would not build air. he was a driver for a o/o. he had a part off the top of compressor.I remember seeing a gasket & a spring or 2. we was trying to figure out how to replace.I told him sorry I cannot help him. I have no idea how the air sys works. was hoping he needed something, that I could help him with like, tools, or a spare hose or clamp. when I got back home & talked to my mechanic, he told me what the unloader kit was for & how it worked. I went to truckpro & bought 1 for my truck as a spare. $12.00 8 months later mine was leaking bad. lucky I had my spare. my truck would also have some of the same symptoms, though not as bad. when the air dropped to 90psi both guages would go quick to 120 & cut out, then back down especially the no 1 tank when on the brakes. one thing I can tell you when checking for leaks. it's o.k. to check while truck is off so you can hear too. but you must also check while truck is running. my unloader gasket would not leak unless truck was running. my fan clutch was also leaking.

one more thing you can do for this & other repairs & parts. get the unloader part num off the receipt. this way if you are ever broke down & cannot move, you can call a parts house or a shop & give them the part number to bring out. this is a good idea for all your parts. have handy your fuel filt, oil filt, belt's,air bag's & a few sensor part numbers. calling someone & telling them I need part xyz is better & cheaper than having them come out & then go hunt for the right part, & since all parts can be cross referenced, all you need is one part number. so if you have a fleeguard filter it can be crossed to donaldson,detroit,cat, e.t.c.
 
Ok i'm about ready to pull my hair out!!! 3 compressors have gone bad in a month!! I have replaced everything(3 govenors,unloader valve rebuild kit,main discharge line,3 compressors and the air dryer) the last compressor was brand new..this all started after the KW dealer pulled my front cover to do the main seal and ass. gear drive bushing.I'm beginning to think they did something wrong when they had it apart and blocked the oil passage causing the compressor to starve for oil. I do have good oil pressure i'm running about 38-40 psi going done the road and 23 psi at idle... Also where does the oil come from to lube the compressor is it thru the ass. gear drive bushing or is it a oil galley?? What do you guys think?
 
I would be talking to that KW dealer about your problems if that is when it started. They should be coming good on it if the problem was caused by one of their techs inadvertently screwing something up.
 
n-14 have a oil press. line from the engine block to the compessor. the line may have been kinked when the comp. was changed.
 
But my question is where does the oil come from, does it come thru the ass. gear drive bushing or is there another route the oil takes?
 
It gets oil through the gear cover. If they used silicone to seal the cover, or damaged the gasket or in the re and re, they could have easily blocked the oil galley behind the cover when they torqued it down.
 
Well I dropped the truck off to day at the stealership. And pointed out the fact that I didn't have any problems with my air compressor until after they pulled the front cover to do the main seal and ass. gear drive bushing. they said they would tear it apart and find out what was going on.I also told them if that was the problem their screw up putting the front cover back on and blocking the oil galley, that they cost me $1050 for the new compressor they put on last time that I wanted my money back and I wasn't paying for them to fix it right this time.(not to mention the work/money I have lost basically being broke down for a total of 2 weeks between the 3 compressors that went bad)
 

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