[Richard]

Hi Larry,

Do you mean the compressor is running, but the system pressure is not climbing? If so, first diagnostic is to disconnect airline downstream of check valve and ensure the air is flowing through the check valve.

Oops, I forgot you may also have the unloader solenoid valve. I am assuming that check valve is downstream from unloader. If you have airflow downstream of check valve then both are good. If not, you will have to remove the check valve to see if the unloader is passing air.

I don't know if this applies to you or not, but two of the unloader solenoid valves I tried were pilot operated. Meaning the solenoid didn't really open the valve, it opened a passageway in the valve body to allow air to flow. The air flow then opened the valve. So what, you say. If the system did not have any pressure, the valve would not open, since the air required to open the valve was on the opposite side of the valve from the compressor. If for some reason I didn't have any system pressure, the aux compressor would open the valve. And since the 12V compressor is check valved to only provide seal, potty, and door air, it wouldn't help to open the valve.

Sounds like you are having "fun". If you get totally frustrated with the diagnostics, try this. Just hard pipe the air line to the compressor. Leave the unloader and check valve out. See if it will build system pressure. If it does, you know that the problem is in what you left out. If it doesn't build system pressure that way, then we are all working on the wrong thing by fiddling with the check valve and unloader.