I had the same problem with my S70 since new. It would only happen when the outside temperature was in the 90s and I sat in a parking lot waiting. Over the years it happen more often and at lower ambient temperatures. Don't waste your money on sensors until you determine if electrical power is getting to your compressor clutch. If all your sensors are working properly your system will be sending power to the compressor clutch to ingage. If it is getting power the problem is an internal thermoswitch that is sensing an overheat condition. When the compressor cools down the thermoswitch closes the circuit and the a/c works again for several minutes until it heats up again. I have read that some Volvo techs have found a way to short out the sensor to make the A/C work. I was unable to find one so I had to have the compressor replaced. Expect to pay around $800.