-
AIR LEAK AT ENGINE COMPRESSOR
This one’s got me stumped…so far. Year or two ago, started to notice an audible air leak in the area of the engine driven compressor when the engine was shut down. The leak was intermittent and stopped after a few minutes with no serious loss in pressure on any of the dash gauges…brake 1, 2 or aux.
Now the leak is louder and occurs virtually every time I shut down. Haven’t found it yet. Checked hoses but this seems unlikely. Guessing it’s some sort of unloader or pressure valve. Anyone?
1999 XLV X-6872, liberty #440 -
15 Replies
-
The leak stops after a while?
I bet if you take a pressure reading at the Schrader fill valve at the RH side below the tail light stack you will find the leak stops when that hits zero. It should have no affect on your system pressures.
-
Yes, the leak stops after 10 minutes or so and sound like it’s coming from the rear of the compressor.
-
I’m not saying the leak is OK or acceptable but would like to pin down the possibility of it affecting or not affecting the systems in the coach.
I am trying to remember how my previous coach was set up and I think your coach has the governor at the compressor. The reason for my brain heading in that direction is to see if it is associated with the signal line or the governor for example.
1999 XLV X-6872, liberty #440 -
I can check the schrader valve tomorrow and advise.
-
You might try shooting some soapy water on that three inch bellows(baby air bag) that tensions your over the road air conditioning compressor belts.
-
Joel, we have very different buses, but I also have hissing for about 5-10 minutes after engine shutdown. Mine comes from the area of the air dryer, which on my bus is outside the engine bay behind the tag axel. I also have a few ping tanks in the area so I’m not positive of the source. Mine hisses for 5 to 10 minutes and then the air shuts off decisively, like a valve has snapped shut. It seems to me that it’s a pressure relief that closes when it hits a designated pressure. Like you, my dash gauges don’t change during the hiss. Is your air dryer in the vicinity of the compressor? Mine has always done this, so I assumed it was normal.
-
Joel when the wet tank drians it does not effect the gauges there will be a line running from the wet tank to the compressor / governor check lines at comp on governor , there is a check valve at primary tank after it leaves wet tank ,it can not drain primary tank if its at wet tank or to the compressor, I also think yours will have a second primary tank that is just in front of the motor up high there is no check valve on that one it is very hard to see it can also leak from the feed line or the pet cock ,tank is not that big , it is behind the primary tank at back of bus
-
Bryan: Yes, my receiver/dryer is located fwd of the drive axle and the leaking noise I hear at shutdown doesn’t come from there. Pretty sure it’s not normal as I didn’t notice it at all until a year or two ago and it’s definitely getting worse now.
Jon: You hit the ball; still don’t know if it will be a home run. The leaking stops when I bleed off air pressure at the rear schrader fill valve to about 60psi. BTW, I’ll be posting a question on HVAC soon that’s probably right up your alley.
-
Thanks, Joel. Now I need to find out if mine is broken, or normal for MCI.
-
I hate to admit this, but I have to dig around to be able to properly and accurately describe why. I did know many moons ago when I experienced that, but right now all I think I remember is the loss of air is only after the compressor cycles off and it does not affect pressure in any of the tanks or pneumatic systems.
Would anybody believe me if I said my brain has so much information when a new piece of information is inserted, one of the old pieces of information falls out?
-
No, I don’t believe it.
IF it only leaks air after cycling off, it’s no big deal but wouldn’t that be true of everybody’s? I’m more concerned with it leaking constantly when pressure is up which I can’t hear because of engine noise and the possible implications of compressor overwork or major failure on the road. If I could identify the source of the air, I could check to see if leaking when compressor is running. I suspect, however, something is actually wrong or everyone would experience this (and mine wasn’t this way in the distant past) and I want to get it fixed at MY convenience as opposed to a truck stop’s convenience.
-
Joel,
You do have a leak which is why you hear air. However that line with the Schrader valve on all coaches will show full system pressure, but over time, if nothing changes such as the engine running to cycle the compressor that line goes to zero pressure. That is normal. Undoubtedly you should not hear a leak because it means your compressor is pumping air to atmosphere, but I don’t think the leak in the line to the Schrader valve will cause the loss of air in the systems.
Anybody out there able to bail me out on this one? If not I have to pull out some pneumatic diagrams. I think it is the signal line to the governor.
-
If that line goes to the gov’ner and the leaking stops when pressure in the line is reduced, sounds like it would be a leak in that line or the gov,ner??? I’ll wait till you check a schematic but I’ll see if I can find one on Prevost. Is the gov’ner replaceable?
-
do they auto dump when you shut coach down? Around that period they had that function briefly.
-
Not tags.
According to the schematic, the scrader valve line goes to the drier and a line from the drier labeled ‘control’ goes back toward the compressor and appears to terminate in mid-air near the compressor!?!? Could I have a problem in the drier venting air to an outlet near the compressor??
Log in to reply.