tennsmith
Well-known member
Just prior to Christmas I posted an article on how the air dryer on our Itasca coach had failed and left us stranded overnight at a rest area. This is the promised follow-up on what happened. New Year's eve presented a 65 degree day so I scrambled under the motorhome and removed the entire air dryer unit. In the process of removing it, I actually brushed against the black dessicant filter atop the unit and it turned!! That most certainly should NOT have happened. Not knowing if this was the failure or what, I continued with removal of the dryer and ordered everything that could be replaced in/on it, feeling guilty for not servicing it before it failed.
I found nothing amiss inside the dryer but replaced all valves, check valves, the heater, and the two filters anyhow. At one point, I thought the heater element had failed, but then later learned from reading Haldex material that the heater is equipped with a temperature sensitive switch that is open if the air temperature is above freezing. This allows the heater to operate only in "below freezing" temperatures and I guess its purpose is to prevent any freezing of water captured inside the unit. Unfortunately, I had already tested the heater at room temperature and it was open so I ordered a replacement prior to discovering the thermal sensor, so now I have a spare.
The culprit, however as best I can determine, was the loose dessicant cannister. All I can postulate as a failure mode is that the dessicant cannister was not tightened sufficiently when replaced at some time in the past. This initial "looseness" combined with vibration and particularly the cold weather (the trip where it failed was the coldest weather in which we had taken it on the road since we've owned it) caused the gasket seal to shrink a bit and lose it's resilience, thus losing the airtight seal with the housing. Once air began flowing beneath the seal, any/all contact with the dryer housing was lost and vibration just caused it to get worse. The check valve within the dryer unit prevented any of the stored air ahead of it from escaping, but the poor air compressor was just pumping against an essentially "open" line. I guess since there was no significant air pressure being generated, there was no loud "hiss" from the leaking dryer and the noise of the diesel was loud enough to hide the low pressure leak. This loss of air seal happened sometime previous to our stop and the process of braking and use of the emergency brake, associated with the stop, depleted the air in the storage tanks to the point where there was not sufficient air pressure to remove the emergency brake, thus we were stranded.
I have learned a lot from servicing the dryer and will construct a separate post which is suitable for the library on how to service the unit. Until I got into it and started reading about it, I thought it was a passive device consisting of two filters, but it is a bit more complicated than that and needs to be serviced/maintained regularly and perhaps "overhauled/refurbished" at 5-10 year intervals. What I found inside mine was a lot of road grit/grime despite the shield that is intended to prevent such material from entering.
I found nothing amiss inside the dryer but replaced all valves, check valves, the heater, and the two filters anyhow. At one point, I thought the heater element had failed, but then later learned from reading Haldex material that the heater is equipped with a temperature sensitive switch that is open if the air temperature is above freezing. This allows the heater to operate only in "below freezing" temperatures and I guess its purpose is to prevent any freezing of water captured inside the unit. Unfortunately, I had already tested the heater at room temperature and it was open so I ordered a replacement prior to discovering the thermal sensor, so now I have a spare.
The culprit, however as best I can determine, was the loose dessicant cannister. All I can postulate as a failure mode is that the dessicant cannister was not tightened sufficiently when replaced at some time in the past. This initial "looseness" combined with vibration and particularly the cold weather (the trip where it failed was the coldest weather in which we had taken it on the road since we've owned it) caused the gasket seal to shrink a bit and lose it's resilience, thus losing the airtight seal with the housing. Once air began flowing beneath the seal, any/all contact with the dryer housing was lost and vibration just caused it to get worse. The check valve within the dryer unit prevented any of the stored air ahead of it from escaping, but the poor air compressor was just pumping against an essentially "open" line. I guess since there was no significant air pressure being generated, there was no loud "hiss" from the leaking dryer and the noise of the diesel was loud enough to hide the low pressure leak. This loss of air seal happened sometime previous to our stop and the process of braking and use of the emergency brake, associated with the stop, depleted the air in the storage tanks to the point where there was not sufficient air pressure to remove the emergency brake, thus we were stranded.
I have learned a lot from servicing the dryer and will construct a separate post which is suitable for the library on how to service the unit. Until I got into it and started reading about it, I thought it was a passive device consisting of two filters, but it is a bit more complicated than that and needs to be serviced/maintained regularly and perhaps "overhauled/refurbished" at 5-10 year intervals. What I found inside mine was a lot of road grit/grime despite the shield that is intended to prevent such material from entering.
