I have an '88 760 turbo wagon that has just had the air conditioner serviced (switched over from R12). It works fine (for Volvo air) unless I have the re-circulate on when it will stop blowing air if any load is put on the engine. ie ...going up a hill or any kind of acceleration. The blower sounds like it is still trying to push air but I get no air flow. To me, it seems like some interaction with a drop in vacuum. I've had this problem before and after the service so it isn't something that was done during the R12 conversion. I believe the 2 vacuum check valves under the hood (on top of the intake), were replaced a couple years ago.
Any clues ?

Thanks for any help,
Michael