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Aux Air Pressure Switch
My pressure switch in the steer bay started leaking this weekend out of the pressure release pin/valve, I replaced with a new switch, but after the aux pump shuts off, and the switch contacts the pin valve, the air leaks down to 90 lbs. and turns the pump back on. This continues on and on, back and forth, where as before, after reaching 120psi, the pump shut off, and didn’t come back on until air dropped below 80 psi.
Why does it even need the little pin valve in the picture? Is it like a pop off valve? It’s connected into the same air coming from the compressor.
Isn’t the aux air protected somewhere else as far as building up too much pressure.?
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15 Replies
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Did you replace with the exact same part number ? There are so many part numbers available …..it’s a problem.
The whole ship is regulated at 120 LB with Prevost air topping off at 130 lbs max. Prevost AUX air is normal 120 LB max.
This pressure switch can be adjusted both min and max pump on/off. I dialed mine down to 80lbs. to run less.
Overall this pressure switch is very reliable and rarely do we read about malfunction.
AL
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The only switch I could find locally was the same other than instead of a 125psi shut off, the new switch is a 175psi. I dialed it down to 120psi by loosening the lock nut on top of the spring. The problem is, when it reaches 120psi, the pump shuts off, but the arm activates the bleed valve, and immediately lets the pressure down to 80 psi and the pump comes back on. It does this continuously.
If I remove and plug the bleed air line, it works perfect. So, why do I need it?
Couldn’ I install a 120psi pop off valve and do the same thing?
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I think it’s a safety pressure blow off.
If you can locate the exact original part number…I believe your problem would resolve.
When I had trouble with this valve…Marathon suggested the exact part number as spec per coach build. Located mine on ebay.
Hope this helps…I share your frustration.
AL
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That seems to be a remote type exhaust that relieves pressure when the compressor cycles. I don’t see any problem with eliminating it as you suggested Jerry and adding a separate relief. Usually compressors have the exhaust as part of the assembly.
I set mine at 90/70 since it all my Marathon side air needs are low pressure and regulated.
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Thanks,
I’m gonna try that, I’ll post results later.
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Jerry,
No offense to anyone, here is what that device really does.
That device is a pressure relief valve for the compressor. It’s purpose is to bleed all the air pressure out of the supply line from the compressor to the first check valve/ air reservoir (tank) when the air pressure reaches the high pressure switch set point turning off the compressor. Later when the pressure drops to the pressure switch start point, this permits the compressor to start (first few seconds) with no initial load (back pressure) on the compressor. This allows the compressor to start more easily, reduces the electrical load on the motor and electrical system, and ensures that the motor will not stall on start up and possibly blow a fuse/breaker. It greatly enhances the the life of the compressor motor.
If it leaks continuously, there is another component that has failed. Likely a check valve. Usually somewhere in the line that goes to the tank. The check valve can be anywhere AFTER where the pressure relief line T’s off of the line from the compressor to the tank.
Not trying to stir up anything, just trying to point you in right direction for troubleshooting. Good luck.
With the right pictures we might be able to spot the offending component. Maybe pictures of supply line after the Tee that branches to the pressure switch line.
Hate to speculate and send you off in the wrong direction but in picture #3 the line above the gauge has a check valve in it. Is that the supply line for the tank?
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I admit to being surprised to see that type switch used in the application. I have only had Liberty coaches, but my aux compressor pressure switch is nothing more than a switch that opens at a certain pressure, and closes at a lower pressure. For my purposes I have cut out at 80 and cut in at 60.
I has no other function that to open and close the switch controlling the compressor and does not relieve air pressure back to the compressor.
There are likely some applications that require pressure back to the compressor to be bled off so the compressor does not restart under load, but I was surprised to see that type switch on a coach.
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This is my 3rd Featherlite, and all of them have had the same Square D Pressure switch, but this one has the bleed line.
That could be a check valve I’ll look closer.
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Fixed!
Tim, you were correct, it was the check valve causing the problem. The bleed valve is supposed to leak air out of the line from the compressor to the switch when it reaches max pressure. It was letting all the air out because the check valve was bad. Good catch!
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Glad I could help.
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I am having the exact same issue…..where exactly did you find the defective check valve ? Which T was it on yours? Thanks
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Most likely the pressure release is connected by a tee and the check valve is usually on the down stream of that tee.
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Marius, it was directly below where the 1/4″ line for the bleed off valve goes into the air source from the pump, just above the pressure gauge in my pictures above. Very easy to replace, just make sure you pay attention to the arrow on the check valve, and install it in the right direction as to air flow.
I bought a check valve from a local Fleetpride truck shop, it was actually for a brake system made by Bendix, but works great.
1999 XLV X-6872, liberty #440 -
I don’t have a check valve there…..I looked everywhere…and there is no check valve on the compressor output line in the generator compartment. Somebody modified the system it seems…..
I have to chase some leaks. The Aux compressor starts every 30 min and runs about a minute.
Anybody can tell me what is part of the Aux system on a Vantare ? I know about the pocket doors, generator airbags, engine tensioner bags it seems, stairwell cover, what else ? I have electric dump valves and Headhunter toilet that does not seem to need air.
I took off the 1/4″ line with needle bleed valve from the pressure switch so that the tab does not push the needle anymore and so far, the compressor starts and re-starts fine without problem.
Took off the line off the compressor head to see if I have any air bleed back and I don’t…so there is a check valve somewhere in-line but I just can’t find it.
The needle valve does not leak when in closed position but will bleed the air out of the system 4-5 times out of 10 if I let it connected to the pressure switch….sometimes it bleeds the line as it should, sometimes it keeps bleeding air, pressure drops under 75 psi and the compressor restarts….weird…
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They are hard to see, some of them look just like a union fitting or nipple joining two fittings together. You could always put another in to stop that.
Also, leaving the bleed line plugged off would work until you can find or install one.
I wouldn’t worry about it too much. If I hadn’t found mine, I was just going to cap it off.
Post a good close up picture of your steer bay, maybe someone can see it, as they did mine.
Nothing else that a Vantare uses air for, other than what you mentioned, unless you have an overhead swing down TV up front.
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