Frick RXF Unt has a problem with its XJF 120 compressor Unloading.

[Grizzly]

Ok. Mahmoud.
Thanks for the update.
You have me foxed that's for sure.
Historically I had a similar situation and was able to prove the slide operation with Nitrogen.
By disconnecting the slide oil feeds at either end and then pressurising either fitting.
You have to be careful of the surplus oil that drains out though.
Once I had proven that the slides physically moved I replaced the relevant solenoid block.
Which solved the problem.
You use the term loading unloading solenoid block. There are 2 blocks one lets the oil into the relevant end of the slide piston. The others bleeds away the oil at the opposing end.

So if you are pushing at the return slide end the opposite end should allow the oil at that end to be drained away. Just a thought! it may just be worthwhile proving the mechanical operation of the slide through its valves.
Because the piston unloading spring will naturally take over at the comp stops as the oil pressure forcing the slide open drops off, you will find the slide returns when the comp is turned off!
Grizzly