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ISL Engine driven air compressor constantly cycles

Yahoo Message Number: 115432
I've noticed the air dryer purge valve discharging every few minutes while driving, even though the pressure gauge indicates about 120 PS is being maintainedI. My understanding of the air compressor is that it should cycle off at 120 PSI when the purge valve discharges, and not cycle back on again until PSI drops down to about 90. I've changed the air governor and the frequent discharge continues. I took the coach to Cummins to have the dryer cartridge replaced and the purge valve rebuilt. The frequent cycling of the compressor continues. The Cummins tech who rebuilt the purge valve told me the frequent cycling of the compressor shouldn't be a concern with the relatively low mileage of a motor home compared to a high mileage commercial vehicle. I'm skeptical and would hate to to learn too late that the constant cycling of the compressor caused it to fail at a most inappropriate moment.

I'm curious if anyone here has experienced similar issues or concerns? Because the Cummins tech told me not to be too concerned about it I'm hesitant to throw money at a fix if unwarranted. Dos anybody else notice frequent operation of the purge valve even though the PSI remains close to 120?

John Coleman
'02 Intrigue 11467

Re: ISL Engine driven air compressor constantly cycles

Reply #1 –
Yahoo Message Number: 115434
I have noticed ours doing the same thing but haven't replaced governor yet. Keeping an eye on this.

Re: ISL Engine driven air compressor constantly cycles

Reply #2 –
Yahoo Message Number: 115436
John

Did the purge valve get rebuilt? I have a C-9 so we are not talking about the same unit; but, when I replaced my air dryer I was told that they no longer produced the purge valve re-build kit. My purge valve does not cycle repeatedly.

Dan 2006 2006 Allure 31348 (C-9)

Dan

Re: ISL Engine driven air compressor constantly cycles

Reply #3 –
Yahoo Message Number: 115437
Hey Dan - How long ago was this? I had rebuilt kit put into our unit at OMC about 18 months ago. (But possible they still had some in stock. And suppose the Allure's with C9's could have a different units?)

From memory, we have a Bendix AD-IP in our 04 Allure with ISL. And I believe I remember Colton saying it was sort of an odd unit, as many coaches had I believe the AD-9. Colton kept rebuild kits available for the AD-9, but had to have a parts delivery swing by with the kit for the AD-IP.

OP - Any signs of moisture as you bleed your system?

As FYI. I've never had noticeable moisture when bleeding my air system. I supposed due to the Western USA travels we most frequently due, with lower humidity. (Well, except the Olympic Peninsula has just a tad of moisture in the region:)!)

Best to all,
Smitty

04 Allure 31017
04 Allure Sold to a nice new owner! Now enjoying a 07 Magna Rembrandt 45' ISX600 #6775
"We're ONDROAD for THEJRNY!" (Toad and Coach license plates, say Hi if you see us!)

Re: ISL Engine driven air compressor constantly cycles

Reply #4 –
Yahoo Message Number: 115443
I did have the purge valve rebuilt, and there hasn't been any moisture discharge from tank bleed valves. I've been able to find a handful of web site discussions about frequent cycling air compressors There are a few likely culprits, but with the rebuilt purge valve that eliminates one. Other possibles are the air line between compressor and governor or to dryer might have leak, or the compressor unloader valve is faulty. A few other possible causes too.

I bought the coach 4 years ago and have put on about 18K miles. This being my first vehicle having air brakes I didn't realize that short cycling isn't normal and I've been merrily rolling along But after reading that short cycling is the most common cause of a failed compressor, now I have another item for the immediate to-do list.

John

Re: ISL Engine driven air compressor constantly cycles

Reply #5 –
Yahoo Message Number: 115444
Not good. He is home but we are not going to the lake as he is too weak. They had the grandkids come this past weekend and that wore him out.

I think it's finally hitting Julia. He isn't rebounding from this.

BVL
2003 Country Coach
Allure 1st Ave 30900

Re: ISL Engine driven air compressor constantly cycles

Reply #6 –
Yahoo Message Number: 115448
I would check for an air leak. The air line from the wet tank to the governor, purge valve, ride height valves.
The air pressure gauge only reads pressure on the primary and secondary tanks. The governor works off the wet tank pressure. So, you could be leaking air, but the pressure gauge shows full pressure. The ride height valves work off the wet tank. Does it cycle when your parked and the engine running?

Bill

Re: ISL Engine driven air compressor constantly cycles

Reply #7 –
Yahoo Message Number: 115468
John

Are you losing air pressure over night? I had leaking ride height valves and I would get up in the morning and the pressure in both tanks would be low. After a couple of days would be down to zero.

Dan 2006 Allure 31348

Dan

Re: ISL Engine driven air compressor constantly cycles

Reply #8 –
Yahoo Message Number: 115470
Thanks for the information about wet tank line to governor and ride height valves... I didn't realize this is the arrangement. The primary and secondary tanks don't show significant loss after being parked for weeks at a time and so I thought leakage wouldn't be the problem. This gives me something to look at...