Awhile ago I saw a post re heater servos dropping out under acceleration. My 92 960 would drop the A/C every time I climbed a low incline or booted it to go round. I found a quick and easy fix with the installation of a vacuum storage tank. I went to a Pick and Pull, found an older Saab and pulled the vacuum storage tank from it. They were routinely used in all the Saab cars and I think even in some older Volvo models that didn't produce enough constant vac for the climate control. It is installed under the right hand fender in the Saab. Then I built up the rquired air line adaptors and inserted it in series with the heater servo vacuum line outside the firewall. After the fix I could climb long grades and always had A/C.