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Topic: Air system and gauges questions (Read 348 times) previous topic - next topic

Air system and gauges questions

I have been working on air leaks to the 1999 U320 air system.  Found and fixed a protection valve and drain valve on the front right tank.  I also found a big leak at my air horn switch under the dash.  Since working on the leaks I have sprayed soapy water on all connections I have found.  My lower gauge on the dash is holding rock steady at 110 psi but the upper gauge is initially at 110 but goes down to around 45 psi in about an hour then holds steady.  See picture attached.  I know the top gauge is connected to the horn and other things.  I have some questions about the gauges and what they are connected to.  As you can see from the picture, both gauges are quite different in pressure, upper at 35-40 psi and lower at 110 psi.  I thought they should be similar.  Should they be so different?  Please describe the items on each of the gauges on the dash.  The air system schematic does not make that destinction/i.e. confusing.  Brakes on which gauge, air bags on which gauge (??), etc.  Are there check valves in the lines that would make the pressure at the gauges so different? 

Greatly appreciate the help.  Thanks.  Jerry
Jerry Poettker
1999 U320 40', build #5561
2015 Lexus RX350 w/ Tow Dolly

Re: Air system and gauges questions

Reply #1 –

So the gauge that is dropping is indicating a leak. This leak can be at a check valve and you will never see bubbles because it is leaking internally. Through isolation you can just keep searching and isolating till you find it. You can also use an ultrasonic listening device. By placing on each fitting and valve, you will hear the air leaking internally. obviously check the easy things first. Like drain valves. Has the desiccant filter been changed? Was there any signs of the filter failing i.e. white powder? Can easily isolate by just opening the drains to see which tank is empty. Lines, valves, filters, solenoids, regulators, leveling valves, airbags, leveling, solenoid packs, and everything in between Can leak internally and is difficult to find.
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Re: Air system and gauges questions

Reply #2 –
Scott,

Thanks for your reply.  I found no desiccant powder coming from any drain valve on the tanks.  I do not know when the last time the air dryer components were changed/replaced/rebuilt.  We have had the coach about 20 months.  Upper gauge was again at zero this morning and lower gauge was low (30).  Crawled under the front of the coach and right tank had pressure, nothing on left tank.  Gauge between front tanks was at zero.  Step gauges were at zero. Opened drain valve on back tank and was at zero pressure.  I would really like to solve the leaks but I am thinking they are all now internal leaks.  I don't have a sniffer but may get one in the future.  The coach is useable as is so I'll continue at a later date.  I'm still trying to figure out what is on each dash gauge by taking notes as I mess with the coach.

The Amazon link did not work. It seems to be incomplete.  I'll check the tanks again in the morning as it seems to leak down over night on the systems on the upper gauge.  Thanks.

Jerry
Jerry Poettker
1999 U320 40', build #5561
2015 Lexus RX350 w/ Tow Dolly
 

Re: Air system and gauges questions

Reply #3 –
Fixed link. Sorry.  Just an example, havent purchased. I replaced my entire dryer when I bought the coach with a rebuilt unit and replace the desiccant filter annually. Sometimes a couple month late, but that was the plan. Will replace the dryer again at the five year date