I have a 2006 Monaco Diplomat and I'm having trouble with the rear air suspension. When I try to dump the air before leveling with my jacks, the rear air bags don't seem to go all the way down like they should. The front dumps fine, but the back stays partially inflated.
I'm still pretty new to RV maintenance and not sure where to start troubleshooting this. Should I be hearing air escaping when I activate the dump? What are the most common causes when rear air bags won't dump completely? Any guidance on what to check would be really appreciated!
Rear air bags not dumping fully indicates a stuck exhaust valve, check valve issue, or height control valve problem. Listen for air exhausting when dump is activated. Check for obvious blockages and try manually releasing air via Schrader valves on bags.
Your 2006 Monaco Diplomat's rear air bags aren't fully deflating because there's likely a faulty dump valve, restricted air lines, or a problem with the leveling system's solenoid valves. The rear air suspension has independent dump valves that control deflation, and when one or both malfunction, the bags won't release all their air like the front ones do. This is a common issue on Monaco coaches of this vintage, especially with the HWH leveling systems typically installed.
The most common culprit is the rear dump valve solenoids sticking or failing to open completely. On your Diplomat, these are usually Hadley or similar brand valves located near the rear axle area. Over time, moisture and debris can cause the internal mechanisms to stick partially closed, preventing full air release.
Another possibility is restricted or kinked air lines leading to the rear bags. The rubber air lines can deteriorate after 15+ years, developing internal restrictions or complete blockages. Check for any obvious kinks, especially where lines route around the frame or suspension components.
The leveling system control module could also be sending incomplete dump signals to the rear valves. Monaco coaches from 2006 typically use HWH or Kwikee leveling systems, and the control boards can develop issues with relay contacts that don't fully energize the dump valves.
Finally, the air bags themselves might have internal damage, though this is less common than dump valve or control issues.
Basic hand tools including 9/16" and 1/2" wrenches for air line fittings, screwdrivers for electrical connections, and a multimeter for testing electrical circuits. You'll also need a can of soapy water solution for checking air leaks.
Have replacement dump valve solenoids on hand - for Monaco coaches, these are typically Hadley part numbers H00412C or similar 12-volt air valves available for around $40-60 each. You may also need DOT-approved 3/8" air line if replacements are needed.
A basic air pressure gauge will help you monitor system pressures, and electrical contact cleaner can help with corroded connections. Safety glasses are essential when working with pressurized air systems.
Start by locating the rear dump valves, typically mounted on the frame rail near the rear axle. With the engine off and parking brake set, manually activate the leveling system's dump function while listening to each rear valve. You should hear a distinct "whoosh" of air - if one side is quiet or weak, that valve is your problem.
Test the electrical supply to each dump valve using your multimeter. With the dump function activated, you should read 12 volts at each valve connector. If voltage is present but the valve doesn't open, the solenoid is bad and needs replacement. If no voltage is present, trace the wiring back to the leveling control module.
Before performing any electrical testing or valve replacement work, first ensure all air pressure is released from the system for safety. To replace a faulty dump valve, Disconnect the electrical connector and mark the air line positions before removal. Remove the mounting bolts and install the new valve in reverse order, ensuring proper torque on air fittings (typically finger-tight plus 1-2 turns or per manufacturer specifications).
If valves test good, inspect the air lines for restrictions. Disconnect lines at both ends and blow compressed air through them - they should flow freely. Replace any lines that show internal collapse or restriction. When reassembling, ensure fittings are properly seated (most pneumatic fittings use O-rings or tapered threads that don't require sealant) and test the system thoroughly before putting the coach back in service.
Call a professional if you find multiple system failures or if the leveling control module itself is malfunctioning. These units can be complex to diagnose and often require specialized knowledge of the specific system installed in your Monaco.
If you discover air bag damage or height control valve problems, these repairs often require chassis work and proper lifting equipment that most DIYers don't have access to. Professional shops also have the proper tools to pressure test the entire system safely.
Electrical issues beyond simple valve replacement, especially problems with the main control board or complex wiring harness damage, are best left to RV technicians familiar with Monaco's specific systems. The labor cost is usually $100-150 per hour, but a proper diagnosis can save you from replacing unnecessary components.
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