Re: Stairwell Cover Not Working
Reply #12 –
As stated above, there can be several explanations for the 2 dash air gauges reading different pressure, especially after the coach has been parked for a while. You are correct, however, in your understanding that this pressure reading difference might be caused by a leaking inlet check valve on one air tank. If you wish to spend a little time and effort, you can test your "faulty inlet check valve" theory by conducting a simple trouble shooting routine that eliminates the "parked for a while" time variable.
1. Run engine until air compressor cut-out (air dryer purges). Shut off engine. The wet tank and both brake tanks are now at the same exact pressure (approximately 120 psi).
2. Check (record) the reading on both dash air pressure gauges.
3. Open the water drain valve on the WET tank (see air system schematic), and allow pressure to bleed off to zero.
3a. What came out of drain valve? Dry air is good. Water, or oily grey "mud", or dry white powder is not so good. Time to service air dryer.
4. Check (record) the reading on both dash air pressure gauges.
5. If both dash gauges read the same pressure in step #2 and step #4, then the inlet check valves on the respective tanks are good. 
Clarification: With "good" check valves, the "front" and "rear" air tanks should not immediately lose any pressure when you drain the wet tank.
6. If either, or both, of the dash gauges lost pressure (in the few minutes) between step #2 and step #4, the inlet check valve on the respective tank is faulty, and should be rebuilt or replaced.
If it turns out you have one (or two) bad check valves, they are not super expensive. Changing them out is not complicated, but can be somewhat difficult depending on how easy it is to get a wrench on the valve.
If they are OEM and have never been removed or replaced, they can be very TIGHT.
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Topic: Stairwell Cover Not Working