[BusNit]

After a few months of sitting dormant and tons of work that I performed, today I took it out for a drive. Rear brake air check valve seems to work now and built up pressure when I exhausted the air from the brake test. I wanted to make sure it would build up air. That said, I brought along my compressor just in case. I drove for about 50 miles with smiles on my face. This thing rides oh so nice and smooth. One of the things I did over the winter was install an LED indicator lamp next to the Jake brake switch which is tied to the circuit going to the engine solenoids. When engaged, the light turns on so I know the solenoids are getting power. Seems to work although I really don't feel the braking force. I never had a 2 stroke before so I have nothing to compare it to other than my 2018 Ram Cummins diesel. That truck will almost stop itself on jakes alone. New front a/c works phenomenal and I am thrilled to have a comfortable drive again. Now that it is parked over the pit where I can get to the wet tank, I will remove it, have it cleaned and replace any and all check valves I find back there. I am thinking of removing the auto drain under the wet tank and putting in manual drain valves where I can access them without getting under the coach. It was a good day.

[MrE]

I can't help you with the Jake brakes, mine never worked on my 8V92 before it blew. I do know about compression braking on motorcycles, a four-stroke slows down better letting off the gas than a two-stroke with a compression release. It sounds like although you're getting juice to the solenoids, they're not working.
Congratulations on the front AC! That will make it nice, seems to be an issue with a lot of Newells.

[BusNit]

I took it to a local Detroit dealer who swapped $600 from my wallet to say the jakes are working properly. Took them a week and I received the coach full of mud and road dirt. It was a couple weeks into the new paint work...

Regarding the solenoids, I manually tested them and they do click on and off without the engine running when I had the valve covers off.
Yeah, the A/C was an expensive affair but one that was needed. The better test is when it is over 110º out. Hard to keep any coach cool when underway.