Aux leveling system compressor

[Chargerman]

I pulled my compressor because it isn’t working. When my Coach is level and I leave the system on (HWH) after some time my system will exhaust air to keep it level. The compressor never came on since I’ve owned the Coach (8yrs). I’ve confirmed that the compressor works and the pressure switch also works. The pressure switch opens at approx 90 psi. I know that the two wires on the plug are  both for 12vdc+ And I’ve confirmed that it functions properly on the bench. I have also confirmed that the plug on the Coach is supplying 12 to the red wire. The other wire on the plug should provide 12volt when the system recognizes that it needs the compressor to turn on. I don’t know how to force this to happen. Does anyone know where these wires come from on the Coach?  I want to confirm continuity and also check the fuse. 
 

Thanks!

[Ivan K]

My compressor only comes automatically on when level can not be reached by deflating. But I can force it on with any up-arrow (in manual mode). BTW, the signal wire comes from the controller itself.

Edited July 20, 2022 by Ivan K

[vito.a]

When we purchased our coach the aux compressor did not work.  It took me several months and a steep learning curve to finally get it working. 

I replaced the following parts:  Thomas 405ADC38/12 compressor, Nason pressure switch in the pump assembly, the 15A blade fuse in the pump assembly wiring, and finally the White Rodgers solenoid.  

There are some great diagrams in the link below (#24 and 29 by CountryB).  

https://www.irv2.com/forums/f115/replacing-hwh-auxilary-air-pump-369684-2.html

The best way to test the Aux compressor is to level the coach.  Then dump the air by pumping the brakes several times.  Turn ignition to ACC, Depress the Air button once (this places the system in manual mode).  Now depress any of the Up arrows.  The system will command additional air and switch on the aux compressor.  Remember, it's very quiet as it's the same compressor used in dental offices.  

If your Thomas 405ADC38/12 Aux air compressor isn't working with 12v applied directly, you can purchase a new one on eBay for $399 or a used one for about $200. A rebuild kit is also about $200.  

[Tom Cherry]

37 minutes ago, vito.a said:

When we purchased our coach the aux compressor did not work.  It took me several months and a steep learning curve to finally get it working. 

I replaced the following parts:  Thomas 405ADC38/12 compressor, Nason pressure switch in the pump assembly, the 15A blade fuse in the pump assembly wiring, and finally the White Rodgers solenoid.  

There are some great diagrams in the link below (#24 and 29 by CountryB).  

https://www.irv2.com/forums/f115/replacing-hwh-auxilary-air-pump-369684-2.html

The best way to test the Aux compressor is to level the coach.  Then dump the air by pumping the brakes several times.  Turn ignition to ACC, Depress the Air button once (this places the system in manual mode).  Now depress any of the Up arrows.  The system will command additional air and switch on the aux compressor.  Remember, it's very quiet as it's the same compressor used in dental offices.  

If your Thomas 405ADC38/12 Aux air compressor isn't working with 12v applied directly, you can purchase a new one on eBay for $399 or a used one for about $200. A rebuild kit is also about $200.  

Mine is probably simpler than the HWH systems, but should work on the same principle. The pressure switch (typically an ON @ 90 PSI and OFF @120 PSI0 is T'ed into the main "leveling circuit".  Don't get me into the check valves, there are diagrams. When the air bag pressure leaks down below 90 PSI, the aux compressor comes on. That can actually be a "physical leak" or when the motor home "moves" as in someone walks and one corner might "shift", the Auto Leveling will cycle. Get enough of the tweaks and the air will go down...bingo...you hear it run.

Some of us, and others with far more experience, will either use the auto level or level manually....then turn OFF the auto level to prevent the MH from moving around.  

Good Luck...

[Chargerman]

Thanks guys for the reply’s and info. I am very confident that my compressor works properly. I will try to pump down the pressure and then put it in manual and ask for it to raise an end and see what happens. I also have the HWH manual so I will see if it tells where the signal wire fuse is. Be back to you tomorrow. 

[Tom Cherry]

9 minutes ago, Chargerman said:

Thanks guys for the reply’s and info. I am very confident that my compressor works properly. I will try to pump down the pressure and then put it in manual and ask for it to raise an end and see what happens. I also have the HWH manual so I will see if it tells where the signal wire fuse is. Be back to you tomorrow. 

Progress.  FWIW, my Valid system may be different.  My compressor feed is just a plain, always HOT, FUSED 12VDC line….going straight to the pressure switch, then from there, to the compressor.  I do not know if the HWH has a more exotic or sophisticated system…..whereby there is some sort of signal or line that nuts feed 12VDC and the pressure must be below 90 PSI.  I BELIEVE we have prints in the files….search for WIRING DIAGRAM and make sure that the FILES option is checked..two pages of them.  
 

Good Luck.  BTW, I do know that folks with Dynasty HWH systems, probably very similar, to yours do not like the annoying “pump comes on at odd hours in the early AM and switch off the AUTOLEVEL.  My switch was corroded and it was 4 years before I found it and put in a new switch.  Then it got annoying and now it only comes on when I tweak the level in MANUAL.  I never leave it in AUTO and never drop a corner or have it sag..

[Chargerman]

HWH is similar except it has a second 12v wire for signaling. The first wire is always hot and it goes to the main lug of a relay with the other lug feeding the pump. The signal wire goes through the pressure switch and then to signal terminal of the relay. Then other terminal on relay goes to ground. I have to find out why I apparently am not getting power to the signal wire. 

[Chargerman]

Ok so I tested the compressor by letting down the air pressure and asking the coach to lift and the compressor works. Now I have to wait until I’m out in a week or so and see if it kicks on at all. In the past the Coach has always just exhausted air on one side or the other to keep it level. Will the compressor only come on if I dump all of the air then level?

[Ivan K]

1 hour ago, Chargerman said:

Ok so I tested the compressor by letting down the air pressure and asking the coach to lift and the compressor works. Now I have to wait until I’m out in a week or so and see if it kicks on at all. In the past the Coach has always just exhausted air on one side or the other to keep it level. Will the compressor only come on if I dump all of the air then 

 By dumping air, do you mean from the touch pad or brake pedal? Brake pedal dumping does not effect bags but you know that. Normally it will start raising if one of the bags that would need to be dropped to obtain level only has like 10 psi left. It won't let it drop anymore and will air up which ever ones are needed and aux compressor comes on. To prevent twisting. Hope it makes sense?

[Chargerman]

I meant dumping the air on the touchpad and then leveling. I don’t do that but I know some folks do. I have always got to my spot and hit the level button twice to let it auto level. My suspension looses very little air but after a few days the front or rear will exhaust some air to maintain level. I’ve never heard the compressor come on

[Ivan K]

I don't think that you have a problem. It just did not come to a situation where it needed air. If it did and the compressor wasnt running when it should, you would get Excess slope light.

Now if there still was enough air in your tank, that air would be used as long as it is above the PPV pressure whether the compressor works or not.