The RECIRCULATION and AC OFF lights are flashing after start up. The owners manual says that this indicates and HVAC Fault. It does not do this everytime I start-up, only randomly. Also everything appears to work during this time. I can cycle the AC on/off, turn recirculation on/off, adjust the temp, adjust the fan speed, and the auto functions appear to work. How can I determine what is causing the "fault"?

I forget what year your car is but you will need to pull codes from the A/C system.

It is a 1998 S70 GLT. Can the codes be read with a regular code scanner or is this some Volvo thing?

I think you need to have Volvo do it unless you have a real expansive one that reads A/C codes.