2000 Volvo S70 Intermittent A/C issue

Air Conditioning problem
2000 Volvo S70 Front Wheel Drive Automatic 154500 miles

My A/C has an intermittent fault -- the fan keeps blowing, but the cooling stops. I've not detected a certain cause, but it happens in traffic, on the interstate, and sometimes if I start or stop quickly or gun it to accelerate. My mechanic says the coolant is to spec, but it didn't happen during the day he had it.

Turning off the A/C switch on the dash for a few minutes will -sometimes- cause the cooling to start again when I re-engage it.

Any ideas? This is one of the 2000 S70s that has continual electrical shorting issues -- tail lamps going out, etc. Could that be involved?