There are three possible problems I know of that are simple to check. First, get yourself one of those pressure check and recharge items from a place like NAPA. Charge the system according to instructions. If the problem persists it could be the temp sensor on the compressor that can be bypassed and is not even used on newer models. There also is the change the air gap on the compressor clutch is too great in which case it needs to be adjusted. Bay thirteen has good stuff on that all. Thus far I have had those three problems on a couple of the FWD Volvo's. Also, there is the sensor above the grab handles that needs to be kept clean. This is above the doors. Just vacuum them out to keep dirt from building up and fowling up the sensors.

Good luck,

dick