Originally Posted by Don B

The desiccant is supposed to adsorb moisture from the ambient air as it is inhaled into the air suspension system by the air compressor. From time to time, the Air Suspension Control Module (ASM) commands the exhaust solenoid valve to open, allowing some of the "dried" air in the air suspension system to backflow through the desiccant bed. This is supposed to partially reactivate the desiccant.

In practice, the desiccant beads eventually encounter so much moisture that they become waterlogged and the "reactivation" procedure does little if anything to dry the beads. This is why I and many other members have replaced the desiccant beads when we replaced the piston ring/seal.

mhamilton and I were discussing this procedure and while reviewing some Wabco training documents, I was reminded that for some of their air brake systems they state that the desiccant may need to be replaced every two years. The desiccant for those systems is packaged in a spin-on canister similar to an oil filter. Unfortunately, Wabco made no provision for easy replacement of the desiccant in the compressors it designed for Jaguar/Audi/Porsche etc.

Cheers,

Don

Originally Posted by 2ndeagle

Correct.

Desiccant has a point of expiration.
I worked 20+ years in Telecom maintenance. All of our air-compressos have desiccant canisters, much like air brake systems. Starts off blue, order a can when it gets to violet in color, better have it replaced before it turns pink or risk reprimand.

Originally Posted by Don B

When I was shopping for molecular sieve desiccant beads, I did find that some beads used a color-changing technology, but either because they were more expensive or did not come in the sizes I was seeking I opted for plain old non-color-changing beads. I figured that if I had to remove the compressor and open up the desiccant bed to check on the color of the beads, I might as well be prepared to just replace the beads.

I happened to run across this link in my bookmarks yesterday, which may be relevant to this discussion:

What Are the Most Common Desiccant Bead Materials Used in Air Dryers?

Cheers,

Don