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cebunting
cebunting, Contractor
Category: Heavy Equipment
Satisfied Customers: 8
Experience:  Tractor Trailer and reefer repair since 1999
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A 2005 T800 with a cummins isx 450..Periodically..compressor..kick

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I have a 2005 T800 with a cummins isx 450. Periodically while driving the air pressure drops below where the compressor would normally kick in. When this happens, air pressure continues to drop as air is used, to the point where the low air warning buzzer sounds. Air pressure will not build. When this happens, the only way I can get air to build is to shut the engine off, wait a minute, then restart the engine. When this is done, air pressure builds normally, and everything is fine again for a few days.

My local shop has replaced the governor and the compressor. The problem persists. Is there an electrical sensor, relay, or switch of some type on these models that may be faulty? Any other ideas what's causing it?

cebunting : Do you know what kind of air drier it ha
cebunting : Sounds like a Bendix AD-IS .... if so that mostlikely is it
Customer: replied 4 years ago.
Not sure what type of air dryer... it's the kind with a spin-on filter. Don't think it's bendix, had one of those on my last truck. This one is smaller than that was. the bendix I had didn't have a spin on filter.
The ad-is has a spin on plus it has a little tank on the side of it.
Customer: replied 4 years ago.
My mechanic says the air dryer is a meritor. He also contends that there's nothing electrical in the air system (other than the heater element in the dryer). It's all mechanical, so stopping and restarting the engine (ie. key off then on) doesn't make sense. I can't just keep replacing parts in the hope that we fix the issue. Can you explain why a dryer problem would cause this to happen?
The ad-IS drier has the check valves built into it, the meritor does not. The drier is not the problem, ask him about the check valve between the wet tank and primary tank. If the wet tank has air the governor will not tell the compressor to operate. If there is a blockage between the wet tank and the primary tank the primary tank will not charge.
Customer: replied 4 years ago.
Would a check valve blockage of this type cause intermittant behaviour? This problem recurs once a week or so. Most of the time everything is ok.
Sorry I misread the question. Are you on the road now or in the shop?
Customer: replied 4 years ago.
I'm at home. I go out again tonight. The truck is parked at the yard, so I don't have quick/easy access to it at the moment.
Customer: replied 4 years ago.
hmmm.... sorry for the confusion on the type of air dryer. I looked at pictures of both online, and was unsure my mechanic was telling me correctly - he was doing it from memory after all and he sees a lot of trucks. I called my vin in tothe dealer, and he confirmed you are correct. It is a bendix ad-IS.

Hopefully that will assist you in pinpointing the problem.
I would say 95% chance the air drier is at fault then. It has valves built into it that are not serviceable...
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