[rcweingart]

That wouldn't explain the frost on the line from the evaporator to the compressor which is supposed to be carrying hot evaporated refrigerant, not cold liquid refrigerant. This is Jeff's situation. I can't speak for other Mark II cars but I kind of doubt that a undocumented reported header heat situation is unique to the Mark II cars and not the original series. I was able to get my A/C to blast cold air by replacing the recirculating factory heater valve with a simple in-line heater valve and adding a shut-off valve to the heater core return line thereby isolating the heater core from getting hot engine water so that it doesn't interfer with and heat up the cold A/C air circulating through the HVAC box.