K 3500 Truck 4WD V8-5.7L VIN R (1998)
Control Assembly: Description and Operation
Control Assembly, HVAC
The air conditioning system on C/K models is electronically controlled. Three backlit, rotary knobs provide full control of the system. These rotary
knobs control blower speed, air temperature, and mode of operation. Two push-to-latch buttons select recirculation mode for maximum cooling and
control over the air conditioning compressor.
The blower speed rotary control has four fan speeds and an off position. When the blower fan is turned off, all HVAC operations turn off also.
The temperature rotary control has 180° of travel. A detent at the full cold-end of travel engages recirculation. Operating the system with the temperature
control placed in this detent will result in maximum cooling. Air inside the passenger compartment will be recirculated through the blower case. Outside
air use will be minimal. Recirculation can also be manually selected by pushing the RECIRC button.
The mode rotary control has three major detents to indicate VENT FLOOR, and DEFROST mode positions.
Placing the control anywhere in between the major detents results in air output blending between the two modes. The recirculation mode is not available
anytime DEFROST is selected, or while air is being blended out the defrost outlets.
Automatic recirculation will occur when compressor head pressures exceed 2275 kPa (350 psi) and disable after head pressures reach 1724 kPa (250
psi). When activated, it cannot be manually disabled by the MAX button.
