My '06 Allergo Bus has a problem with the air system. Once it reaches pressure, about 115#s it blows off pressure every three to four seconds. So far we have replaced the governor on the air compressor and rebuild the Haldex air dryer. My mechanic wants to replace the dryer but it is a $500.00 part. This seems to be too big a gamble without assurances. Any ideas out there? Thanks in advance, BobPS When I disconnect the small hose on the dryer from the governor, the cycling stops and the pressure rises to about 140

The governor does two things - it tells the air compressor to stop compressing air and it tells the air dryer to purge moist air that it has collected. It sounds like the governor is not working properly, or that the compressor is not stopping compressing air. The governor does this by sending full pressure air to the signal port on both the compressor and the air dryer when it cycles into the high pressure position. That tells the dryer to purge and the air compressor to stop compressing. When system air pressure drops below the set point (usually 90 psi or so) the governor cycles the other way (low pressure position) and removes air pressure from those ports, telling the air compressor to start compressing again and the air dryer to shut the purge valve (which has properly been open all this time) and send air to the wet tank.When you disconnect the air line from the governor to the air dryer, you are effectively telling it to stop purging and start passing air to the rest of the air system once again. that is what it is supposed to do when there is no pressure at it's signal port. Was there pressure in the line from the governor when you disconnected that line at the air dryer?Brian

Does your air drier have a check valve between it and the air tank? It is possible that the check valve is bad, and your air pressure is draining out during the purge cycle. causing your system to recycle fast. Replacing the Air drier would be my very last try. Good luck Gary

All air dryers will have that check valve, and indeed it can stick open as suggested. Since the governor gets it's system pressure somewhere after that check valve it can be that the system pressure is dropping really fast where the governor gets it's signal, yet not where the pressure gauge gets it's signal. Good suggestion!Brian

Thanks guys! I knew someone would have good suggestions. Tomorrow I'll look at the check valve and get back with my findings. Bob

An update. I spoke with a tech rep at Haldex and he thought that it was not the check valve but rather the unloader in the compressor. I went ahead and ordered the check valve as it was only $15 so we'll see what happens. I really don't want to have to remove the compressor, i can't even see it! Bob

Air systen cycles (blows off pressure) every three seconds

VintageRacer
Explorer
Aug 25, 2015
The governor does two things - it tells the air compressor to stop compressing air and it tells the air dryer to purge moist air that it has collected. It sounds like the governor is not working properly, or that the compressor is not stopping compressing air. The governor does this by sending full pressure air to the signal port on both the compressor and the air dryer when it cycles into the high pressure position. That tells the dryer to purge and the air compressor to stop compressing. When system air pressure drops below the set point (usually 90 psi or so) the governor cycles the other way (low pressure position) and removes air pressure from those ports, telling the air compressor to start compressing again and the air dryer to shut the purge valve (which has properly been open all this time) and send air to the wet tank.

When you disconnect the air line from the governor to the air dryer, you are effectively telling it to stop purging and start passing air to the rest of the air system once again. that is what it is supposed to do when there is no pressure at it's signal port. Was there pressure in the line from the governor when you disconnected that line at the air dryer?

Brian

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Air systen cycles (blows off pressure) every three seconds

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