Volvo: 92 Volvo 940 T A/C: Fan Blows but No Cool Air, pep boys, volvo 940

Question
"Pep Boys" diagnosed the issue as a failed master control unit.  I had the upper-level valve replaced about 2 months ago. Worked fine but now, nada.  Can you confirm the diagnosis or suggest others.  Also, can you provide a repair procedure(s) so I can save time?

Answer
David,
To confirm the diagnosis I need to see the car and preform all the needed tests. If  you do not trust them take the car to a shop that works on Volvos and get there opinion. I have though seen a lot of the controls head to fail by not allowing the power to flow to the A/C compressor.