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Old 05-17-2003, 08:19 AM   #1
rdm
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Air compressor headaches.

Our compressor builds up the right pressure but lately seems to be blowing off a releif valve when the high pressure is met.
Where can I find additional info on this unit?
Any suggestions to correct the problem.
It seems to happen when we are driving down the road both air bags are at proper inflation.
Last fall I pulled the fuse on the compressor and stopped regularly and the air ride bags stayed up properly.

Thanks in advance for your thoughts
Ray
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Old 05-17-2003, 01:07 PM   #2
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Relief Valve

Ray:

Check the pressure in your tank via the Schrader valve on the very bottom of the volume tank. If it is still holding pressure, everything is copasetic. There is a relief valve that exhausts to atmosphere whenever the compressor cuts out. This is designed so that the compressor does not start against a pressure head. The relief valve blows off the line to the volume tank, and a check valve on top of the volume tank holds pressure in the tank.

If you lose pressure thru the blow down valve, you might want to repair/replace the check valve. Mine on the ’87 was chock a block full of some sort of sticky substance. After cleaning, all is working OK.
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Old 05-17-2003, 01:42 PM   #3
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Thanks Dennis,
The tank is holding pressure.
This occurs with the compressor running and the system is pressured up thats what is confusing. It will continue untill you pull the fuse. after replacing the fuse the compressor will run a very short while (seconds) and stop normally. Then later you will notice this air noise with the compressor running.

Thanks
Ray
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Old 05-17-2003, 01:45 PM   #4
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ok, this brings up my older problem that I am getting nearer to be able to work on. Too many projects too little time!! Add a job and family to that and well....
If I jack up and support the back end with jack stands, can I disconnect the air bags from the compressor, and take the comp. out to see if I can fix it? And while at it, can I just put in a manual valve for input and forget the compressor? My bags don't have a leak I can find, but the comp is dead will blow a big fuse whenever it starts up. If I could safley manually add air, and check the level I would be ok.
Lastly. would it make more sense to go the over the spring air bags as additional help? I see these for about 300 installed.

Peter gave me some ideas on the compressor issue but I have not yet been able to do anything with it. I just bought a larger jack and some stands, so i am getting ready....
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Old 05-17-2003, 02:17 PM   #5
 
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I just happened to stumble unto that on another forum, I think it relates to your question:

"I had the air bags on my gas coach. I was too cheep to spend the $$$ for that system [compressor], so I bought a 12 volt air pump. not much adjustment is needed anyway"

Several people answered that they did the same, using a hand gauge, and bypassing their existing compressor. As long as they don't have any leak in the first place, not much adjustement was necessary.

Hope this helps.
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Old 05-17-2003, 08:29 PM   #6
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Been there -- What I done

Alan:

I’m not sure how the linkage/airfill valve is set up on a single axel, but on a dual axel, whenever you put the drive axel on jacks, or even raise the rear end with the stabilizing jacks the air bags will blow the volume tank down. I don’t know if one of my valves is leaking, or it’s just doing what it’s supposed to do, but if I use the stabilizing jacks the air system slowly bleeds off. My owner’s manual states that it is normal for the compressor to come on when it is started, so I expect that Airstream built some sort of a slow leak into it since they made mention of the fact that compressor operation is normal at startup. When my air bleeds off totally the main spring (the rear of which is shortened for the tag axel) is actually is resting on the frame. Just putting air in the tank will not inflate the bag; it has to be driven s short distance before the bags fill. I assume this action is due to the way the level sense valves operate. Since to lose pressure appears to be normal, I would recommend installing a gauge somewhere on the system (my ’87 has none, only a “low pressure” idiot light), in order to monitor the system. As I stated earlier, without air in the bags, my springs are hitting the outside flange of the frame, so I really need air available at all times.

On another related note, the PO had installed an aftermarket compressor in my unit. It draws 22 amps (Info Plate), and was fed by a 12 gauge wire with a 25 amp fuse in the dash. I don’t think that I could afford enough 25 amp fuses for a long trip. When I cleaned the Electrical Contacts on the start/charge system I ran a 4 gauge wire to the compressor area, protected the new feed with a 30 amp flat mount circuit breaker, and installed a standard relay activated by the original 12 gauge feed.

No more blown fuses, plus some extra amperage available in the rear area to relay/fuse lights and electric brake for the Saturn Toad.

Ray:

The first thing I would check on your system would be the feed to the blow down valve and the pneumatic/electric switch contacts. Sounds as if maybe the blow down valve is not closing all of the time. My sympathies looking for a “sometimes” electric problem. It is so frustrating when everything works at checkout, then fails as soon as you get on the road.
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Old 05-17-2003, 09:01 PM   #7
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Quote:
Originally posted by rdm
Thanks Dennis,
The tank is holding pressure.
This occurs with the compressor running and the system is pressured up thats what is confusing. It will continue untill you pull the fuse. after replacing the fuse the compressor will run a very short while (seconds) and stop normally. Then later you will notice this air noise with the compressor running.

Thanks
Ray
Ray,
there is only one thing in the system that tells the compressor to turn on and off:
The pressure regulator
It's the grey or black box close to the compressor. It has a diaphram that is set by an adjusting screw to close or open contacts to feed 12v to the compressor.
Its a very inexpensive replacement item (less than $10.-) but make sure it has the proper cut-in/cut-out settings (80/100psi)
or you have to install an inline pressure gauge to set it.
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Old 05-17-2003, 09:20 PM   #8
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Quote:
Originally posted by ALANSD
......If I jack up and support the back end with jack stands, can I disconnect the air bags from the compressor, and take the comp. out to see if I can fix it? ....
IF you are not under your rig, you don't have to jack it up to disconnect the compressor.
You may even find that the bags stay pressurized once the compressor is disconnected, which would indicate an inline check valve further down the line.
Just relief the pressure slowly!!!
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Old 05-18-2003, 12:32 PM   #9
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Ray - Air Blowing while Comp. is Running

Ray:

Further reflection indicates the possibility that your blow down valve could have a mechanical or electrical defect.

Like I said, the blow down valve opens when the compressor cuts off, this bleeds the air line from the compressor to the air tank to "0" psi. The check valve at the top of the holding tank is "supposed" to prevent the air leaking back from the volume tank, and out of the open blow down valve. When the compressor comes back on line the blow down valve closes, allowing air output from the compressor to pressurize the tank.

The purpose of the blow down valve is to prevent the compressor to have to come on line against 80 psi or so of pressure.

The compressor has a chance to come up to speed while pumping up (pressurizing) the line from the compressor to the check valve on the top of the volume tank. This eliminates part of the amperage surge required for compressor startup, and wear and tear on the normally pressurized parts of the compressor (discharge valve and piston rings if the discharge valve leaks).

On the '87 a separate line continues up from the aux air fill and feeds the pressure sensor on/off switch, as well as the electric "idiot light" low psi sensor.
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Old 05-18-2003, 08:01 PM   #10
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Thanks for the ideas

Thanks everyone
your comments and ideas are welcomed.
This week we will check into the problem further
Once again thanks
Ray
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Old 05-18-2003, 08:45 PM   #11
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hi
i went thru a learning experience last year with my rear air bags. some units have one leveling valve and others have two. mine had one and it was a breeze to fix it after i looked at the mess for a while and got lots of help from the forum. when you start your unit up the pump/compressor comes on and the leveling valve or valves bring your unit to the pre set height. if this isnt happening you have something wrong with the leveling valve(s). when you jack the unit up to level the leveling valve will vent the air out of the bags. so you dont blow them. the compressor is not a big issue really any compressor that will pump the holding tank to 100 lbs is all that is required.or you can go to the bottom of the tank and put air in. the pressure switch turns the compressor on and off, YOU CAN CHECK MOST PRESSURE TANKS WITH A TIRE GUAGE ON THE BOTTOM OF THE TANK. the valve on the bottom of the tank needs to be vented some from time to time to get the water out of the tank. hope that makes sence my service manual isnt a lot of help.
i see compressors in some of the parts cats i get for 35 to 40 dollars that has a fan and the claim the unit can run for 8 hours and not damage the compressor. but you do need the current a small wire wont work. blown fuse in a hurry. lol
al
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Old 07-20-2003, 06:02 PM   #12
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Exclamation Compressor update

To day I had the chance to work on the air ride system.
The compressor fills the tank to 110 lbs (measured at the valve on the tank) then the relief valve blows off tank pressure goes down to 100 lbs but the compressor keeps running and running and keeps repeating thi s cycle never shutting off.
Does this mean the high pressure regulator needs replacing
Appreciate your help with this
This year has been the year of inside upgrades
New Dometic 2820
New Atwood water heater
We also installed a Fantastic Fan and new Winegard antenna
Hopefully the compressor is a smaller fix
Thanks
Ray
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Old 07-20-2003, 06:54 PM   #13
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Ray,

It sounds like the pressure switch that starts/stops the compressor is not sensing that the operating pressure has been reached. It is the gray box Peter mentioned. Before replacing it I would try to adjust it. It may just think it needs to get to 115 PSI and it can stop. It sounds like the shutdown pressure should be in the 108 PSI range.
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Old 07-20-2003, 07:03 PM   #14
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i would check two things. the check valve would be first and the pressure regulator that turns the compressor on and off. i would back the pressure regulator off to 100 lbs and see what happens after i make sure the check valve is ok. lol
al
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