Vacuum locking hubs

I have had an issue with my vac hubs not engaging.
At first I diagnosed it as a vacuum leak due to perished rubber hose, after replacing the hose the system still didn’t operate properly. The Green light flashes a few times, then goes solid but there is no clunk. After playing around with it for a bit I noticed the vac line to disengage the hubs has constant vacuum so when the vacuum to engage it goes on it doesn’t work because both sides are in vacuum. If I take off the disengage hose and press 4wd it engages fine because one side is atmospheric and other is vac how it should be.

any idea why the disengage hose has a constant vacuum?

Thanks for this tip, where is the best place to attach the compressor nozzle?

Thanks

I put a couple psi of air in the line but it still has constant vac.
Is there anything else it could be it do I just need a new solenoid now?

One more thing to try which is swapping the solenoids around. If the problem moves with it then you need a new solenoid, They are plentiful, available from anyone who has fitted manual hubs.