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Pure Air Plus filter replacement question

March 21, 2018, 06:07:41 pm

Three years and 18,000 miles ago we had the Haldex Pure Air Plus air dryer replaced with a rebuilt unit. I was told by a knowledgeable person that the desiccant filter should be replaced every three years and the complete air dryer changed out around every five years. We've had no issues with the air dryer and the holding tanks have never had moisture in them.
I purchased a L31120 partial rebuild kit that included the desiccant and coalesing filters, purge shield, and relief valve. The coach has mainly been driven in drier enviroments and less than 10 times driven in the rain.
I removed the desiccant filter (which was clean except for a few tiny pieces of dirty grit by the screens), then the coalesing filter (which was dirty and a little oily but definitely not soaked with oil). There was a 1/4-3/8" thick layer of a yellowish, oily substance below and to the outside of the coalesing filter in an area that looks like it may have been designed as a catchment area for contaminants. Strangely, the old desiccant filter feels like it weighs the same as the new desiccant filter. It seems that the old filter should weigh somewhat more do to the moisture it would have accumulated during operation.
I removed the yellow oily substance with a micro cloth and replaced the coalesing filter but held off on replacing the desiccant filter for now.
Questions. What caused the yellow oily substance and is it normal to have some oily contamination in the area below and to the outside of the coalesing filter? Would having the oily contamination in and of its self be a reason to automatically change the desiccant filter? Shouldn't an old desiccant filter weigh somewhat more than the new filter do to absorbed moisture?
Any input would be greatly appreciated? Gary

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Re: Pure Air Plus filter replacement question

Reply #1 – March 21, 2018, 07:56:31 pm

Our Haldex desiccant big filter is heavy.  I don't think the desiccant absorbs moisture and get heavier from accumulator water.  The 'junk' that accumulates during a drying cycle, gets blown out the bottom after the compressor cycles (that is the sound we hear).  The large wide bottom holds 'stuff' until it gets blown out.

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Re: Pure Air Plus filter replacement question

Reply #2 – March 22, 2018, 12:00:48 am

Check haldex website for change intervals, I have a Bendix and RVs fall into a different category due to lower mileage.

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Reply #3 – March 22, 2018, 11:15:21 am

Thanks for the replies. I spoke to a Haldex tech support guy this morning. He said basically the same thing as Barry about the desiccant filter not absorbing water (not gaining weight) and that the desiccant filter expelled the water during each purge cycle. He also said that the accumulation of contaminants outside of the coalesing filter was normal and that the dryer was designed to expel the contaminants during each purge cycle. He thought the yellowish oily substance was probably produced by the air compressor. He thought that 3 years was a little too long of an interval for changing the desiccant filter because motorhomes generally sit a lot and the desiccant filter is affected by the moisture in the air even more than a vehicle that was constantly being driven. I assume because the moisture would be constantly removed during use. Even though the tech thought the desiccant filter should be changed more often than every 3 years, the region of the country where the motorhome was primarily used and parked would be a major factor in determining the change interval.
If the tech was correct in that the yellowish oily substance came from the air compressor, would the air compressor loose lubrication oil over time and need replenishing?

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Re: Pure Air Plus filter replacement question

Reply #4 – March 22, 2018, 11:33:57 am

The compressor oil is the engine oil. It is recirculated through the compressor. Bad rings on a compressor let oil into the air output.

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Reply #5 – March 22, 2018, 11:39:36 am

Same info as I got from Bendix for our AD-IP. They say every six years, mine is overdue, last replaced in 2010, but the rep said since the coach lives in "The Dry Country" not to worry. I am going to replace it this year with either a fresh or re-man unit.

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Re: Pure Air Plus filter replacement question

Reply #6 – March 22, 2018, 04:17:08 pm

Thanks for the additional input. Craneman, hopefully the rings in compressor aren't too worn. The tech did say that some oily residue is normal. The filter installation guide said to inspect the bottom of the coalescing filter cavity for contaminants or debris and that the presence of solid contaminants or debris indicates the purge valve, Turbo-Saver valve and outlet check valve should be serviced and/or replaced using kit#DQ6020.  Ours only had a few tiny pieces of solid debris. Wish I had taken one of the yellowish oily substance before cleaning it. I did go ahead and installed the new desiccant filter. I'll add a few pics if I can figure out how to add pics to this post.

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