You need to check if the valve works and if the vac circuit it is opening/closing flows freely, but sounds like it is getting power as expected.
Heres the full wiring diagram for the AC:
If you are seeing 9.8V at the solenoid (E) instead of ~12V, probably you are seeing some voltage drop due to the compressor clutch (F) and it is nothing to worry about.
If you take the solenoid out and connect the pins to battery +/- you should be able to activate it. If you connect two hoses to it, and suck through one, you should find it is blocked when the solenoid is disconnected from the battery, but allows air through when it is energised.
If the solenoid is opening/closing as expected, then next check the vac hoses to/from it. You should be able to blow air through them. If you can't, you can try putting some carby cleaner and bottle brush into the vac ports to clear them.
It may also be worth taking the throttle body off and cleaning it as it also can complicate idle, especially with an H cam.
