I had posted a problem with my 94 c280 a/c blowing hot out of door vents and cool out of center ones. I had a chance to t/s it today and found the heater control valves not shutting due to possibly a electronic switch problem. I pulled the connector off and found the center pin had 12v all the time and the outer 2 never recieved voltage no matter what position the heater control was in. the valves never closed causing hot coolant to flow through the heater cores all the time. To test my theory, I clamped off the feed line and disconnected the electric circulator pump and BINGO ice cold air out of every vent. Now there are 2 ways to fix this- 1. either the dash switch or the ECM controlling the valves needs to be replaced$$$$$$$$$$ OR 2. install a $10. ball valve in the feed line close it and disconnect the circulating pump until fall ,then open the valve and reconnect it.(very similar to the way things were done years ago on big rigs and old pickups.) The choice is yours. Hope this helps some one else keep their cool.