The dashboard heater/ AC slide control cable on my 1978 Volvo 244 has broken behind the console where it connects to the blower case. This cable switches the climate control from heater to AC. Now it is stuck on heater and with the summer coming it is becoming unbearable. Is there any way to manually operate this mechanism? I think it operates a door or shutter in the blower case. I can't find any diagrams or schematics except one in my Haynes shop manual that is totally useless. Can anyone help me?