I bought this car about 18 months ago, and the A/C did not work. Two weeks ago, finally paid the cash to get the A/C working (new compressor and expansion valve), and R12 recharge, and now my car overheats very quickly. Highway driving, the temp. gauge rests right in the middle of the gauge, as it always has, but after as little as five minutes of stop and go driving, the gauge zooms up to near or actually in the red!

Other info:

The coolant was flushed and filled at the proper mixture three or four months ago.

When turning the temp all the way to hot and max fan speed, the temp gauge will return to normal fairly quickly, but in this 95 degree weather, it's just sheer madness.

Yesterday, after a twenty minute drive and the temp gauge almost in the red, I checked the coolant overflow, to see if perhaps it is just the gauge misreading. There was pressure in the overflow bottle which began to escape as I opened the cap. Did not fully remove the cap, as the coolant had flowed in to fill the overflow, and would have spilled out.

I had the work done by my mechanic, who is an independent mechanic, and is not a Volvo expert, but has done good work on my three Volvos.

My questions:

What are likely causes?

Is there some electrical connection that may play a part in this and should be checked?

Thanks in advance!