The constant dying of the a/c every time I went up a hill was getting too much for me in my 1993 960. I hoped against hope that it would be the vacuum check valves in the engine compartment but their replacement solved nothing.
With heart in hand I followed Dick Riess' bypass surgery approach on FAQ for vacuum servos.
If I had followed the Volvo recommended route I would still have my big head up the dashboard.
Some observations:
1. The plastic did not bend back - it broke off! No problem it is all held together now with epoxy resin and duct tape.
To test the vacuum valve I used a 1/4" tube and lung power. I was going to buy one of those vacuum guages but I reckoned it went against the spirit of the operation. Thankfully, it was one the double hose bellows ports (yellow hose) that would not hold a vacuum. If it were one of the other two bellows I would have given up.
I would enlarge the hole in the photo downward another 4 cm to have more room to maneuver (in for a penny, in for a pound).
Place a rag in the bottom of the hole to prevent "bits" falling down. One jewelers screwdriver was consigned to the deep! Fortunately it does not cause any rattles! With the next screwdriver I got the lock washer of the air-diverter post. Lots of patience required here. You can push and pull this post to ease of the bellows retainer. A tight fit!
2. In my car 3/8" nuts held the vacuum "bellows" on. These were a pig to get off. I used a 1/4" ratchet with a universal joint extension stiffened by wrapping it in duct tape.
End of Day One
3. I did break off one of the new studs (a last little tighten I thought, the bellows seem to be made from stiff polystyrene) and used a radio bracket mount to fasten it with self tapping screws above and below bellows.
The air now works like it should- a great improvement.
Many thanks to Dick for this elegant shortcut.
Warning! You cannot overestimate how long this job will take you.
Leave plenty of time to go to stores for extra bits and pieces.
Do not attempt with a sore back or hangover.
I now want to charge the a/c system with refrigerant. What is the recommended max. pressure?

Dan