There is an overheat switch on back of compressor that is too sensitive and was apparently not specified by Volvo to be on the compressors from supplier. Volvo has an overpressure protection on all the R134A systems that will cut out the compressor if dangerous temp/pressure occurs. These switches on the compressor are fine on a system that uses an expansion valve but cause trouble in hot weather on orifice tube systems as in hot weahter the return flow from evap may not contain any unboiled refigerant and the compressor will get hotter but not excessively hot. This same temp level would be indicative of a problem on an expansion system that would mean no oil or refigerant is reaching return line into compressor.
The sytem gets a tad low, which is normal due to loss out of front comp. seal or through hoses over a 2-3 year period, and the switch cuts out prematurely. Bypassing switch is the remedy as long as the sytem has no real leaks of any magnitude. Switch is on back of a/c compressor in the wire to clutch magnetic coil.