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I have a leak(s) in the air system and am wondering if anyone has an idea as to where I should start.  I have sprayed soapy water on the front tank, treadle valve and all hoses and connections that I can reach.  I need to get the coach up on blocks to access the rear tank and surrounding area.  Listed below are the results of my various tests.  
 Note:  I started a thread a couple of weeks ago regarding oil in the air tanks.  I changed out the World American filter to a WABCO oil coalescing filter and it looks like that fixed the problem .  I will wait awhile before I go back to that thread and report success (or whether I have to rebuild my compressor ).          

Parking brake pops at 30 PSI

30 PSI - 125 PSI 1:55
 
Compressor cut out 125 PSI
 
Compressor cut  in 104 PSI
 
Engine off, parking brake off, service brakes on, drops from 110 PSI to 70 PSI front, 50 PSI rear in 2 minutes
 
Engine off, parking brake off, starting pressure 110 PSI, at 1:50 100 PSI, at 4:00 90 PSI, at 6:30 80 PSI
 
Engine running, parking brake off, service brakes on, starting pressure 112 PSI, drops to 103 PSI in 20 seconds, compressor cuts in
 
Engine running, parking brake on, starting pressure 113, after 2 minutes no change (still 113)
 
Engine running, parking brake off, service brakes off, starting pressure 113 PSI, drops to 107 in 1 minute, at 1:40 drops to 104 and compress cuts in
 
Open bottom valve near generator, black hose to dry side of front tank, both tanks drain to 0
 
Open top valve near generator, red hose to wet side of front tank, both tanks drop to 0.  
 
Open rear tank drain, front tank holds starting pressure (120 PSI), rear tank drops to 0

Based on these tests, I have no way of draining only the front tank.  

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It looks like you have a few issues.

First, dropping 9 psi in 20 seconds with the brakes on says you have a leak in the air brake system with brakes applied.  That's a pretty large leak and with a helper pressing the brakes you should be able to find it.

Second, if draining the wet tank cause the front dry air tank to also drain air, you have a failed check valve between the wet and front dry tank.  If your front tank is a dual wet/dry tank that check valve is internal and in most cases to change it the tank needs to come out.

A leak with engine off and brakes off also exceeds 3psi/min.  Once the coach is safely supported, check all tank fittings and the air dryer housing.

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7 hours ago, dandick66 said:

Open top valve near generator, red hose to wet side of front tank, both tanks drop to 0.

In addition to @Frank McElroy suggestion of the wet side/dry side internal check.  My air system supplies air from the front wet side, to the rear dry tank through a "charging check valve".   If you are saying that when you drain the wet tank the rear tank drops to zero also, it may be a bad "charging check valve".  I had to replace mine for this reason.   https://www.finditparts.com/pdpexp/wabco-4341000240-3501386?srcid=CHL01SCL010-Npla-Dmdt-Gusa-Svbr-Mmuu-K3501386-L66&srcid=CHL01SCL010&gclid=Cj0KCQjwr82iBhCuARIsAO0EAZwmYL73XjW9DTsWKzfCXwoZflY5TpbdkOsvXcwXJy7OVxGpkxAZpGgaAvanEALw_wcB

7 hours ago, dandick66 said:

Open bottom valve near generator, black hose to dry side of front tank, both tanks drain to 0

My front dry side tank also has a shuttle two way check valve that will equalize the pressure between the front dry and rear dry tanks.  And in the case of a pressure loss of one of these tanks this valve should isolate the two.  A bad shuttle valve could also be causing the some of your issues.   https://www.finditparts.com/pdpexp/haldex-kn25080-368736?srcid=CHL01SCL010-Npla-Dmdt-Gusa-Svbr-Mmuu-K368736-L134&srcid=CHL01SCL010&gclid=Cj0KCQjwr82iBhCuARIsAO0EAZw3XtBrjnzLBTBOgz2JaulQPz-nCSgSJdxYQgH20oeZl5skwRBMLa4aAk6nEALw_wcB

 

 

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6 hours ago, Frank McElroy said:

It looks like you have a few issues.

First, dropping 9 psi in 20 seconds with the brakes on says you have a leak in the air brake system with brakes applied.  That's a pretty large leak and with a helper pressing the brakes you should be able to find it.

Second, if draining the wet tank cause the front dry air tank to also drain air, you have a failed check valve between the wet and front dry tank.  If your front tank is a dual wet/dry tank that check valve is internal and in most cases to change it the tank needs to come out.

A leak with engine off and brakes off also exceeds 3psi/min.  Once the coach is safely supported, check all tank fittings and the air dryer housing.

Frank,

Thanks.  I looked at the tank and it does have plugs in the side of both the wet and dry sides.  Do you know which side I would remove to access the internal valve?  I might be able to access it without dropping the tank, but it doesn’t look all that hard to remove it.  I need to figure out how to remove the large (5/8)lines.  I tried pressing down with an open end wrench, but that didn’t release the line.  I might try twisting it with a pair of pliers first.

Here’s a photo of my front tank looking fore to aft.  The wet side is to the right and dry side is to the left.  On the wet side, the 5/8 hose runs to the rear tank. 
IMG_3719.thumb.jpeg.d92e11840da5232633ec9c115ec807f6.jpeg

13 minutes ago, Bill R said:

In addition to @Frank McElroy suggestion of the wet side/dry side internal check.  My air system supplies air from the front wet side, to the rear dry tank through a "charging check valve".   If you are saying that when you drain the wet tank the rear tank drops to zero also, it may be a bad "charging check valve".  I had to replace mine for this reason.   https://www.finditparts.com/pdpexp/wabco-4341000240-3501386?srcid=CHL01SCL010-Npla-Dmdt-Gusa-Svbr-Mmuu-K3501386-L66&srcid=CHL01SCL010&gclid=Cj0KCQjwr82iBhCuARIsAO0EAZwmYL73XjW9DTsWKzfCXwoZflY5TpbdkOsvXcwXJy7OVxGpkxAZpGgaAvanEALw_wcB

My front dry side tank also has a shuttle two way check valve that will equalize the pressure between the front dry and rear dry tanks.  And in the case of a pressure loss of one of these tanks this valve should isolate the two.  A bad shuttle valve could also be causing the some of your issues.   https://www.finditparts.com/pdpexp/haldex-kn25080-368736?srcid=CHL01SCL010-Npla-Dmdt-Gusa-Svbr-Mmuu-K368736-L134&srcid=CHL01SCL010&gclid=Cj0KCQjwr82iBhCuARIsAO0EAZw3XtBrjnzLBTBOgz2JaulQPz-nCSgSJdxYQgH20oeZl5skwRBMLa4aAk6nEALw_wcB

 

 

I plan on making my ramps tomorrow, so I’ll be able to slide under and look at the rear tank area.  There are no valves like what you’ve posted anywhere up front.

 

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36 minutes ago, dandick66 said:

Frank,

Thanks.  I looked at the tank and it does have plugs in the side of both the wet and dry sides.  Do you know which side I would remove to access the internal valve?  I might be able to access it without dropping the tank, but it doesn’t look all that hard to remove it.  I need to figure out how to remove the large (5/8)lines.  I tried pressing down with an open end wrench, but that didn’t release the line.  I might try twisting it with a pair of pliers first.

Here’s a photo of my front tank looking fore to aft.  The wet side is to the right and dry side is to the left.  On the wet side, the 5/8 hose runs to the rear tank. 
IMG_3719.thumb.jpeg.d92e11840da5232633ec9c115ec807f6.jpeg

I plan on making my ramps tomorrow, so I’ll be able to slide under and look at the rear tank area.  There are no valves like what you’ve posted anywhere up front.

 

You remove the check valve from the wet tank side.  Attached is a copy of the procedure.

PXL_20230504_224355397~2.jpg

To remove the large hose try an open end flare wrench and give it a good hit to push in the ring.  There can't be any air pressure on the line to release it.

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49 minutes ago, dandick66 said:

There are no valves like what you’ve posted anywhere up front.

In your picture on the left side right behind the ride height control arm is what I believe is the three port shuttle check valve.  Look at the part number stamped on that valve.  On my rig the silver line goes to the rear tank and the green line goes to the spring brake relay.   Your front and rear tanks should still be isolated, even if the internal check valve between the wet and dry side is bad.  Unless, either or both the shuttle and charging check valves are not working.

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1 hour ago, Frank McElroy said:

You remove the check valve from the wet tank side.  Attached is a copy of the procedure.

PXL_20230504_224355397~2.jpg

To remove the large hose try an open end flare wrench and give it a good hit to push in the ring.  There can't be any air pressure on the line to release it.

Thanks.  It’s interesting that they specify a 1/4 inch drive, 1/2 inch deep well socket, but then you use a 1/4 inch to 3/8 adapter and extensions.  I wonder why you just done use 1/4 or 3/8 for the entire process.  I’ll do it the way they say.

I’ll try the flare wrench trick, too.

57 minutes ago, Bill R said:

In your picture on the left side right behind the ride height control arm is what I believe is the three port shuttle check valve.  Look at the part number stamped on that valve.  On my rig the silver line goes to the rear tank and the green line goes to the spring brake relay.   Your front and rear tanks should still be isolated, even if the internal check valve between the wet and dry side is bad.  Unless, either or both the shuttle and charging check valves are not working.

My line routing is the same.  I’ve attached the schematic I got from REV.  I had assumed that since I didn’t see bubbles, that the valve was ok.  But, I guess it can be stuck internally and not show signs or a leak.  I’m still trying to understand the whole wet/dry setup.  Why do they call it a wet tank when it comes from an air dryer (not trying to be a wise guy).  Also, there is a connection from the wet tank to the rear tank, so I don’t know why there’s a line from the dry tank to the rear tank, too.  

18623342_B (Schematic Pneumatics DEKA 43ft) Model (1).pdf

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Posted (edited)
1 hour ago, dandick66 said:

Thanks.  It’s interesting that they specify a 1/4 inch drive, 1/2 inch deep well socket, but then you use a 1/4 inch to 3/8 adapter and extensions.  I wonder why you just done use 1/4 or 3/8 for the entire process.  I’ll do it the way they say.

I’ll try the flare wrench trick, too.

  

18623342_B (Schematic Pneumatics DEKA 43ft) Model (1).pdf 367.11 kB · 1 download

Make sure you tape everything, including your socket! Don't want anything dropping in there 😬!

Let us know how it went!

One of the two lines between tanks is so that if you have a failure on one system, your emergency / parking brake won't come on if you still have enough air in the other system. If both drop below 30-40psi, your E-Brake comes on.

Edited by 96 EVO
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58 minutes ago, dandick66 said:

 I’m still trying to understand the whole wet/dry setup.  Why do they call it a wet tank when it comes from an air dryer (not trying to be a wise guy).  Also, there is a connection from the wet tank to the rear tank, so I don’t know why there’s a line from the dry tank to the rear tank, too.  

Yes, it would be the internal check mechanisms failing that would cause your issues.  The wet tank serves as a secondary water removal if the air dryer is not working for some reason.  Just a mechanical trap.  That is why you want to drain it once a month to see if any water is in there and to confirm the air dryer is working.

The dry tanks supply dry air to the operating systems, air ride system, air horn, leveling, some other pneumatic systems, and for the air brakes.  The two dry tanks, front and rear, provide redundancy of the air braking system.  So if you had some sort of major air system breach or failure to one tank, the other tank stays charged and provides enough air pressure to use your air brakes for braking.  This is the purpose of the shuttle valve.  What you are describing now would indicate that if you had a failure all tanks would loose air and you would not have air brakes and your spring emergency park brake would engage and stop the coach.

If the charging check valve (rear tank) and shuttle check valve (front tank) are sticking, this would explain why all tanks go to 0 when you drain just one of them.  Or it could be a combination of them and the wet/dry internal check.  I would pull them and check there operation. 

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1 hour ago, 96 EVO said:

Make sure you tape everything, including your socket! Don't want anything dropping in there 😬!

Let us know how it went!

One of the two lines between tanks is so that if you have a failure on one system, your emergency / parking brake won't come on if you still have enough air in the other system. If both drop below 30-40psi, your E-Brake comes on.

 

48 minutes ago, Bill R said:

Yes, it would be the internal check mechanisms failing that would cause your issues.  The wet tank serves as a secondary water removal if the air dryer is not working for some reason.  Just a mechanical trap.  That is why you want to drain it once a month to see if any water is in there and to confirm the air dryer is working.

The dry tanks supply dry air to the operating systems, air ride system, air horn, leveling, some other pneumatic systems, and for the air brakes.  The two dry tanks, front and rear, provide redundancy of the air braking system.  So if you had some sort of major air system breach or failure to one tank, the other tank stays charged and provides enough air pressure to use your air brakes for braking.  This is the purpose of the shuttle valve.  What you are describing now would indicate that if you had a failure all tanks would loose air and you would not have air brakes and your spring emergency park brake would engage and stop the coach.

If the charging check valve (rear tank) and shuttle check valve (front tank) are sticking, this would explain why all tanks go to 0 when you drain just one of them.  Or it could be a combination of them and the wet/dry internal check.  I would pull them and check there operation. 

Ok, I have a much better understanding now.  I think I’ll start with the shuttle valve since it’s the easiest to get to.  
I hope I can get to this tomorrow.  I’ll post the results.  
Thanks again 

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Based on your data, it looks like you have multiple issues with your air system aside from the air leaks with the service brakes on or off..

With the engine off, when draining the wet tank, both dry tanks need to hold air pressure.  In your case the front tank goes to zero.  This means that the internal tank check valve between the wet and dry tank has failed and needs to be replaced. 

Also, when you drain the front dry tank the rear tank also goes to zero - that's a bad shuttle valve and it will need to be replaced.  This valve is designed to keep the parking brakes released if either tank holds enough air and with internal check valves not allow air to pass to an empty tank.  The rear dry air tank is your main air braking tank for the drive and tag axles.  If air is lost in the front AUX dry air tank, you would have braking power on the Drive and tag axles only from air in the rear primary air tank.  If you lost air in the rear primary air tank, from the front Aux air tank, you would have braking on the front steer and via controlled modulation of the parking brake you would have braking on the drive axle for up to at least 6 full brake applications.  Once your system becomes fully operational, these safety features will need to be tested to make sure that the parking brake modulation control valves still work.  This can all be done with the engine off and the coach stopped with the wheels chocked.  

It's a bit unusual to have so many issues at one time unless the coach sat a very long time or the air dryer wasn't maintained and a lot of moisture got into the system.  I would not be surprised if the pressure safety valves and the PPV valves on the tanks are also leaking.

At this point, set by step, you'll need to replace the defective components one by one until you get the air system back to a safe operating condition. 

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7 hours ago, Frank McElroy said:

Based on your data, it looks like you have multiple issues with your air system aside from the air leaks with the service brakes on or off..

With the engine off, when draining the wet tank, both dry tanks need to hold air pressure.  In your case the front tank goes to zero.  This means that the internal tank check valve between the wet and dry tank has failed and needs to be replaced. 

Also, when you drain the front dry tank the rear tank also goes to zero - that's a bad shuttle valve and it will need to be replaced.  This valve is designed to keep the parking brakes released if either tank holds enough air and with internal check valves not allow air to pass to an empty tank.  The rear dry air tank is your main air braking tank for the drive and tag axles.  If air is lost in the front AUX dry air tank, you would have braking power on the Drive and tag axles only from air in the rear primary air tank.  If you lost air in the rear primary air tank, from the front Aux air tank, you would have braking on the front steer and via controlled modulation of the parking brake you would have braking on the drive axle for up to at least 6 full brake applications.  Once your system becomes fully operational, these safety features will need to be tested to make sure that the parking brake modulation control valves still work.  This can all be done with the engine off and the coach stopped with the wheels chocked.  

It's a bit unusual to have so many issues at one time unless the coach sat a very long time or the air dryer wasn't maintained and a lot of moisture got into the system.  I would not be surprised if the pressure safety valves and the PPV valves on the tanks are also leaking.

At this point, set by step, you'll need to replace the defective components one by one until you get the air system back to a safe operating condition. 

Frank,                              
I’ve owned the coach  for a little over 5 years.  I installed a dual mechanical air gauge about 2 1/2 years ago.  The coach has the Medallion system and sweep gauges (with transducers).  When you turn the ignition on, the Medallion will display “Engine Not Running “ until you start it, so no PSI display.  Once you start the engine you only get the low pressure alarms until the pressure reaches about 75 PSI.  The dash gauges will work only when the ignition is on.  They aren’t the greatest to read as the display goes from 0-150 on a very small scale.  
                                                      
Ever since I’ve owned the coach it has slowly dropped pressure while driving.  The compressor would built to 125, drop to 115, and then slowly drop to 104 (about 2 or 3 minutes) and then the cycle would repeat.  While depressing the service brakes, the pressure would drop then hold.  What I didn’t realize was that the compressor was just keeping up with the loss and slowly fill.  I never tested for a leak with the engine running and parking brake off.   As far as draining the tanks, before this I never looked at the gauges to see what tanks drained when I opened the valves.  I would open the front valve and then walk to the rear and open it.  
                     
About 3 years ago after I noticed my air was at 0 when it sat for a couple of days, I took the coach to a bus garage and they found 2 brake hoses leaking and replaced them and the governor.  Unfortunately, it still leaked to 0 in a couple of days.  Until I installed the mechanical gauges the only way to read pressure was to have the ignition on.  
                       
It looks I have my work cut out for me.  I have a much better understanding of how things are supposed to work.  The compressor feeds the dryer, which feeds the front and rear tanks.  Since the check valve in the front tank is bad, it appears as one big tank.  It all makes sense now.  I hope I can access the check valve without dropping the tank, but I’m prepared to drop it if necessary.  I’ll post my findings.
                                   
 

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7 hours ago, Frank McElroy said:

If you lost air in the rear primary air tank, from the front Aux air tank, you would have braking on the front steer and via controlled modulation of the parking brake you would have braking on the drive axle for up to at least 6 full brake applications. 

Frank, great post,  could you expound on controlled modulation?  Is that automatic or something I might need to do?  I'm guessing it's automatic and at that time the system would change from air pressure applying the rear brakes to the parking brake spring applying them and air modulating that spring pressure.  Am I even close?

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A problem like this can progress pretty quickly.  In early 2021 my system would stay up for +1 week, then in Nov while on a trip I was surprised one morning when my low air alarm came on after stopping for the night.  So I kept an eye on it, the pressure loss increased quite a bit.  While in TX I did a quick soapy spray bottle test, every one of my PPV's were leaking.  Finally called it quits when the tanks would drain enough to trigger the low air alarm after ~30 minutes, I headed home to fix.

Built 6 ramps (glad I did and have used them multiple times since) and started working on the rig changing all PPV's and any other part that had rubber components thinking age was catching up to the system.  I did have a copy of a schematic for a Dynasty that closely mirrored my rig that had the various parts, hose size/color, and their function.  Working on the system helped me understand it.

Luckily not major other issues,  I decided to change out a bunch of the PTC fittings with new, kept the old as spare and I also built an emergency kit consisting of union PTC fittings, tubing, and some other fittings.  All fits in a 5 gallon bucket that's easily stowable.

Good luck on your fix

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Monacoers] Coach Air Suspension Allowable Leak  Down

I was going through some old Monaco Inc. Files and found this information that was sent to me years ago and thought it might be of interest to the Group as this question of what is the allowable leak down rate on a coach is often discussed here.

D.O.T. Standard Allowable Leak Down. Rev. 06-03-2004

The Department of Transportation (D.O.T.) standard for allowable leak down in the air systems is as follows.

1. A 4 PSI drop in the front air system in a 2 minute time period is allowed.

2. A 4 PSI drop in the rear air system in a 2 minute time period is allowed.

This translates into a 120 PSI drop in a one hour time period. In other words, both needles would be allowed to go to zero PSI in one hour. All of the control valves, relay valves, check valves, etc., have allowable leak rates, even for new components. It is not within the Scope of Monaco Inc., or any Manufacturer, to completely eliminate air leaks. Therefore, the D.O.T. sets the standard for allowable leak down rules in the interest of safety. However, Monaco, Inc.'s leak down rate is set as follows:

Monaco, Inc. Allowable Leak Down

1. A 6 PSI drop in the front air system in a one hour time period.

2. A 6 PSI drop in the rear air system in a one hour time period.

This translates into an approximate 60 PSI allowable leak down rate, for each air system, in the overnight park mode(10 Hours). This is an extremely small air leak. The Monaco, Inc. and other Manufactures standard is 20 times more stringent than the D.O.T. required safety standards, which allows 120 PSI per hour.

 
 
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13 minutes ago, Paul A. said:

Monacoers] Coach Air Suspension Allowable Leak  Down

I was going through some old Monaco Inc. Files and found this information that was sent to me years ago and thought it might be of interest to the Group as this question of what is the allowable leak down rate on a coach is often discussed here.

D.O.T. Standard Allowable Leak Down. Rev. 06-03-2004

The Department of Transportation (D.O.T.) standard for allowable leak down in the air systems is as follows.

1. A 4 PSI drop in the front air system in a 2 minute time period is allowed.

2. A 4 PSI drop in the rear air system in a 2 minute time period is allowed.

This translates into a 120 PSI drop in a one hour time period. In other words, both needles would be allowed to go to zero PSI in one hour. All of the control valves, relay valves, check valves, etc., have allowable leak rates, even for new components. It is not within the Scope of Monaco Inc., or any Manufacturer, to completely eliminate air leaks. Therefore, the D.O.T. sets the standard for allowable leak down rules in the interest of safety. However, Monaco, Inc.'s leak down rate is set as follows:

Monaco, Inc. Allowable Leak Down

1. A 6 PSI drop in the front air system in a one hour time period.

2. A 6 PSI drop in the rear air system in a one hour time period.

This translates into an approximate 60 PSI allowable leak down rate, for each air system, in the overnight park mode(10 Hours). This is an extremely small air leak. The Monaco, Inc. and other Manufactures standard is 20 times more stringent than the D.O.T. required safety standards, which allows 120 PSI per hour.

 
 

Good stuff….experience and also complaining to a dealer on my NEW 2009, still in warranty as well as extended warranty….I would leak down to almost zero, when really cold….like sitting in my driveway In February with average ambient in the mid daily low 40’s.  That would be a 2 day period….NOT COVERED.

OK…in the summer….I could go maybe 6 days….low air…probably close to zero.  In BOTH instances, ….the coach was perfectly level and I did not use (it was broken pressure switch….aux air compressor was fine).  So, I just ignored it. Fixed switch.  Annoying coming on and off.  Shut down “Auto” and it stays level.

But, every 3 - 4 years, my OTR shop bubble tests all lines and fittings.  Usually fixes at least one fitting.  My Wabco started to bubble leak after say 10 years. I could see the average “run” PSI was down 5 PSI or so.  Cheaper to pay them put on my new Wabco than for them to rebuild.

 

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Posted (edited)

Dan, you have to have 3 drain valves.

You stated when you drained the wet tank, the primary dry tank gauge dropped to 0psi. When you opened the primary tank drain valve, after draining the wet tank, did any air pressure come out?

Which chassis is your 2012 coach built on?

Edited by 96 EVO
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4 hours ago, dandick66 said:

Frank,                              
I’ve owned the coach  for a little over 5 years.  I installed a dual mechanical air gauge about 2 1/2 years ago.  The coach has the Medallion system and sweep gauges (with transducers).  When you turn the ignition on, the Medallion will display “Engine Not Running “ until you start it, so no PSI display.  Once you start the engine you only get the low pressure alarms until the pressure reaches about 75 PSI.  The dash gauges will work only when the ignition is on.  They aren’t the greatest to read as the display goes from 0-150 on a very small scale.  
                                                      
Ever since I’ve owned the coach it has slowly dropped pressure while driving.  The compressor would built to 125, drop to 115, and then slowly drop to 104 (about 2 or 3 minutes) and then the cycle would repeat.  While depressing the service brakes, the pressure would drop then hold.  What I didn’t realize was that the compressor was just keeping up with the loss and slowly fill.  I never tested for a leak with the engine running and parking brake off.   As far as draining the tanks, before this I never looked at the gauges to see what tanks drained when I opened the valves.  I would open the front valve and then walk to the rear and open it.  
                     
About 3 years ago after I noticed my air was at 0 when it sat for a couple of days, I took the coach to a bus garage and they found 2 brake hoses leaking and replaced them and the governor.  Unfortunately, it still leaked to 0 in a couple of days.  Until I installed the mechanical gauges the only way to read pressure was to have the ignition on.  
                       
It looks I have my work cut out for me.  I have a much better understanding of how things are supposed to work.  The compressor feeds the dryer, which feeds the front and rear tanks.  Since the check valve in the front tank is bad, it appears as one big tank.  It all makes sense now.  I hope I can access the check valve without dropping the tank, but I’m prepared to drop it if necessary.  I’ll post my findings.
                                   
 

I also have a Medallion display that will display engine not running or low air pressure with the ignition on but when I press the button to go to a different screen I can still get to the tank air pressure screen.  I also have a separate air pressure gauge on the dash.  Don't know if yours is like mine but there should be a way to read air pressure with the engine off to be able to do DOT air brake tests.

3 hours ago, Ray Davis said:

Frank, great post,  could you expound on controlled modulation?  Is that automatic or something I might need to do?  I'm guessing it's automatic and at that time the system would change from air pressure applying the rear brakes to the parking brake spring applying them and air modulating that spring pressure.  Am I even close?

Yes - your thinking is correct.  The system is automatic.  The parking brake is modulated to apply the drive brakes by in effect using the parking brake diaphragms.  Give it a try.  Dump the wet and rear dry tank.  With the parking brake released, you should get at least 6 full brake applications before the parking brake automatically sets due to low air pressure.

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On 5/4/2023 at 8:08 AM, Frank McElroy said:

It looks like you have a few issues.

First, dropping 9 psi in 20 seconds with the brakes on says you have a leak in the air brake system with brakes applied.  That's a pretty large leak and with a helper pressing the brakes you should be able to find it.

Second, if draining the wet tank cause the front dry air tank to also drain air, you have a failed check valve between the wet and front dry tank.  If your front tank is a dual wet/dry tank that check valve is internal and in most cases to change it the tank needs to come out.

A leak with engine off and brakes off also exceeds 3psi/min.  Once the coach is safely supported, check all tank fittings and the air dryer housing.

Also check your air dryer. Mine finally provided air leaks sooooooo bad that when I drove my coach ('06 Sig) the entire system dumped air and my emergency brake like began to flash!!!!!

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2 hours ago, 96 EVO said:

Dan, you have to have 3 drain valves.

You stated when you drained the wet tank, the primary dry tank gauge dropped to 0psi. When you opened the primary tank drain valve, after draining the wet tank, did any air pressure come out?

Which chassis is your 2012 coach built on?

 

1 hour ago, Frank McElroy said:

I also have a Medallion display that will display engine not running or low air pressure with the ignition on but when I press the button to go to a different screen I can still get to the tank air pressure screen.  I also have a separate air pressure gauge on the dash.  Don't know if yours is like mine but there should be a way to read air pressure with the engine off to be able to do DOT air brake tests.

Yes - your thinking is correct.  The system is automatic.  The parking brake is modulated to apply the drive brakes by in effect using the parking brake diaphragms.  Give it a try.  Dump the wet and rear dry tank.  With the parking brake released, you should get at least 6 full brake applications before the parking brake automatically sets due to low air pressure.

I did not know that about the Medallion system.  When I turn the key on and try to select any readings, nothing happens.  I just tried again, but this time I hit “enter” and was able to access all of the screens.  Thanks!  However k if I start the engine and the pressures are low, I get the low air display and cannot clear it until the pressure bulbs to approximately 75 PSI.

I lowered the coach and was able to access the plug on the wet side of the tank.  I figured out why you can’t use a 3/8 socket to access the valve - it won’t fit into the drain plug hole.  The dividing plate is about 19 inches into the wet side.  I took the socket and extension and fumbled around, but could not get it onto the valve, so, put the plug back into the side.  I’m definitely going to have to drop the tank.  I still am not having any luck removing the PTC fittings.  I have tried the flare nut wrench trick, but no joy.  I’m afraid I’m going to break the line at this point.  
                                               
I started the coach to raise it back up off of the stops.  Now, when I drain the wet tank the front tank pressure holds!  The rear tank still drops pressure.  I tried it 3 times and it was the same.  When I open the front (dry) tank, pressure drops in both front and rear tanks.  When I open the rear tank, only the rear drains.  I don’t know if I “unstuck” the valve when I poked around with the extension.  I need to run some errands this afternoon and then I’ll try again this evening.    Even if it gets good, I think I still have the problem with the shuttle valve.  I still need to find a way to get those #$#&& PTC fittings apart.

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1 hour ago, dandick66 said:

 

I did not know that about the Medallion system.  When I turn the key on and try to select any readings, nothing happens.  I just tried again, but this time I hit “enter” and was able to access all of the screens.  Thanks!  However k if I start the engine and the pressures are low, I get the low air display and cannot clear it until the pressure bulbs to approximately 75 PSI.

I lowered the coach and was able to access the plug on the wet side of the tank.  I figured out why you can’t use a 3/8 socket to access the valve - it won’t fit into the drain plug hole.  The dividing plate is about 19 inches into the wet side.  I took the socket and extension and fumbled around, but could not get it onto the valve, so, put the plug back into the side.  I’m definitely going to have to drop the tank.  I still am not having any luck removing the PTC fittings.  I have tried the flare nut wrench trick, but no joy.  I’m afraid I’m going to break the line at this point.  
                                               
I started the coach to raise it back up off of the stops.  Now, when I drain the wet tank the front tank pressure holds!  The rear tank still drops pressure.  I tried it 3 times and it was the same.  When I open the front (dry) tank, pressure drops in both front and rear tanks.  When I open the rear tank, only the rear drains.  I don’t know if I “unstuck” the valve when I poked around with the extension.  I need to run some errands this afternoon and then I’ll try again this evening.    Even if it gets good, I think I still have the problem with the shuttle valve.  I still need to find a way to get those #$#&& PTC fittings apart.

Good to learn about your Medallion system…read more about it.  Yes…you can NOT, BY DESIGN, clear it….you need full air pressure….

Keep learning….PM me a photo of the DIC and your button panel.  I may have the same one and have a Medallion print with all the various inputs.  Each is a GROUND signal…I’ll send it to you…it may be in the 2009 Camelot drawings….need to check.  If not, I’ll update and add.

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@dandick66 Are you sure that when you drain the rear tank the wet tank still holds pressure?   If both your wet tank and rear tank are loosing pressure at the same time, but your front dry holds, then you have a problem with the charging check valve on the rear tank that I mentioned earlier.  

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10 minutes ago, Tom Cherry said:

 

Keep learning….PM me a photo of the DIC and your button panel.   

Ya may want to type that one out completely, especially for those of us that 'no comprende' 🤨!

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3 hours ago, dandick66 said:

 

I did not know that about the Medallion system.  When I turn the key on and try to select any readings, nothing happens.  I just tried again, but this time I hit “enter” and was able to access all of the screens.  Thanks!  However k if I start the engine and the pressures are low, I get the low air display and cannot clear it until the pressure bulbs to approximately 75 PSI.

I lowered the coach and was able to access the plug on the wet side of the tank.  I figured out why you can’t use a 3/8 socket to access the valve - it won’t fit into the drain plug hole.  The dividing plate is about 19 inches into the wet side.  I took the socket and extension and fumbled around, but could not get it onto the valve, so, put the plug back into the side.  I’m definitely going to have to drop the tank.  I still am not having any luck removing the PTC fittings.  I have tried the flare nut wrench trick, but no joy.  I’m afraid I’m going to break the line at this point.  
                                               
I started the coach to raise it back up off of the stops.  Now, when I drain the wet tank the front tank pressure holds!  The rear tank still drops pressure.  I tried it 3 times and it was the same.  When I open the front (dry) tank, pressure drops in both front and rear tanks.  When I open the rear tank, only the rear drains.  I don’t know if I “unstuck” the valve when I poked around with the extension.  I need to run some errands this afternoon and then I’ll try again this evening.    Even if it gets good, I think I still have the problem with the shuttle valve.  I still need to find a way to get those #$#&& PTC fittings apart.

Yep, you have a bad shuttle valve and a bad check valve between the wet and rear dry air tank.  At least these valves are accessible.

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1 hour ago, Tom Cherry said:

Good to learn about your Medallion system…read more about it.  Yes…you can NOT, BY DESIGN, clear it….you need full air pressure….

Keep learning….PM me a photo of the DIC and your button panel.  I may have the same one and have a Medallion print with all the various inputs.  Each is a GROUND signal…I’ll send it to you…it may be in the 2009 Camelot drawings….need to check.  If not, I’ll update and add.

Not sure what the DIC is, but here’s the control panel and dash/display.

 

IMG_3740.jpeg

IMG_3739.jpeg

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