My suspicion is low refrigerant as this is common on P2 Volvos to have the driver's side warm up if the refrigerant is low.
Quicke check for low charge is to run engine at a high idle (1200-1500 rpm) for a few minutes. I have a mailer tube I put on accel pedal and run the power seat forward to hold my throttle. A wooden dowel or old broom handle cut to the proper length also works. After a few minutes find the larger a/c pipe that comes out of center of firewall. It should be cold. If not it is low on refrigerant.
If the line is icy cold then check for the servos that move the doors in climte system to regulate temp not functioning right.
Turn the driver's side temp to to full hot till knob stops , wait a couple of minutes and then turn it to full cold. Do this with engine running and fan on in middle position. Listen and feel for air temp changes and for the sound to change, repeat for the passenger side.
The 2005 and up volvos damper control system can get confused and full travel commanded through full hot to full cold end points may reset it.
If you can't get resolution then it is time to go to a shop that has VIDA or other scan tool that can do COMPLETE vehicle.