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If you are loosing air out of both primary and secondary gauges when parked and park brake on and coach shut off look at park brake valve yellow knob and R14 valve, if they are leaking they will both drain down both gauges together, or the two gauges air lines in steering bay going to gauges up to dash

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Ron,

One thing to be aware of with air leaks is there are so many potential places for leaks to occur you have to see a pattern in order to shorten the investigative process.

Peter’s analysis is on target relative to the brake systems. Typically if both the primary and secondary drain down simultaneously the problem is associated with the system associated with the parking brake. I suspect you can hear it if it is the yellow knob valve you use to apply and release the parking brake. It more likely is a relay valve and that is something relatively cheap and easy to access from inside the rear axle area under the coach floor. If that valve fails you cannot build pressure so it is not a leak to be ignored.

But there are other potential causes including leaking hoses or fittings, an air tank petcock not sealing, etc. Someone needs to get beneath the coach and find the leak.

But you also mention the aix pressure, and that is unrelated to the brake system pressure loss unless you have issues with the check and protection valves between the braking and aux systems. Depending on how your converter set up the aux system your problem there can be easy to solve or a nightmare, but the aux system will cause your compressor to run, but the brake systems should not contribute to that issue. A small voice inside my head suggests if the aux compressor run cycle has quickly increased in frequency and is getting worse, see if you can hear leakage at one of the slide seals.

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While on our way to visit a relative in TN, we had stopped at Jeff’s place, which is close-by, and he took a look at the air system. The Prevost side of the air system was holding pressure as you would expect with typical leaks. So I must have been seeing things when I reported that I was losing ALL air shortly after shutting down the engine. However, the problem still existed on the house side. Jeff and the boys checked underneath the bus and in the compartment under the driver and pinched off various air lines trying to isolate the leak. Even with the air door valves shut-off at the manifold, I still lost all of the house air overnight. A lot of head scratching took place because nobody could figure out where the problem was.

It turned out to be the aux compressor. The original Jun-Air 6 was installed inside the storage area behind the front bumper where some people may stow a spare tire. There was no reason to look there (so we thought), so the compartment remained closed and we continued hearing the compressor kick in and run forever.

I just happened to have opened that compartment to look for a tool, when the compressor came on and I heard a hissing noise.

Come to find out that the compressor was blowing back air out of the air filter nozzle. So … whatever amount of air the compressor generated when it was running, it was soon lost through that nozzle and if I had not been right close-up and next to it, we would not have found it. Or, at least, not for a long time.

I wanted to replace the Jun Air 6 with the same (at a cost of close to $1,000) but after having made several calls to distributors, I learned that nobody stocked this unit and it would have had to be special ordered with a lead time of about 3 weeks.

I found a used unit on eBay being sold by a company at a significant savings but before I hit the “buy now” button, I also happened to have a conversation with Jim McNulty who, together with his wife Nancy, was spending quality time at ETLC having a different kind of leak fixed, which had taken over a week already due to the lack of parts from Prevost.

Jim told me about a compressor which had been used to replace a Jun Air on Bill Bunch’s coach. He had found an inexpensive air cooled compressor at Home Depot. A 1HP compressor with a 1.6 gallon tank for under $2000 – He had it in use for quite a while and highly recommended it to a few people.

I ordered a newer model on Amazon (California Air Tools Model 2010A), being a 1HP with a 2 gallon tank model at a cost of about $1800

The compressor was waiting at our next stop in Nashville. Installing it took a few minutes.

This California Air Tools compressor is VERY quiet.

Bottom line is, with the new compressor in place, aux air is holding very well now for as long as 5 hours before the compressor kicks in at the low end of about 90 PSI to pump it back up to about 105-115 PSI, which takes about 3 minutes.

Yes, I do still have air leaks. Beginning with the air rams on the pocket doors. But, at least, instead of hearing the aux compressor come on every 45 minutes and run for 10 minutes each time, we have regained some control by having replaced the compressor.

Cheers,

Ronald

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2+ yrs ago we removed the noisy failing Gast brand aux compressor and installed a quieter California Air Tools MP100. We built a new box for it to live in since it’s a different shape. Works great, last a long time.

https://www.amazon.com/California-Air-Tools-MP100-Compressor/dp/B005AECACW