Heating and Air Conditioning: Description and Operation

Fig. 2 System input & output components.:

The automatic temperature control system on this vehicle uses various sensors which are installed at the head and foot levels in order to maintain the temperature of both positions at optimum levels. When starting the engine in cold weather, the system immediately operates in the defroster mode until coolant temperature rises. As the coolant temperature rises, the outlet door is automatically switched to the foot level for starting the heating operation. The system begins to control the air flow automatically as the outlet air temperature reaches the optimum level. When the DEF switch is ON, the air flow is automatically set to the HI position. However, the air flow can also be switched to the LO position by setting the manual switch to the LO position. The objective temperature fine control switch (Set Temp. Adjuster) is used. This switch permits adjustments of the upper objective temperature and the lower objective temperature within a range of plus or minus 3.6 degrees F. A manual DEF switch is also used so the system can be fixed in the DEF mode of operation for driving even when a malfunction occurs within the control function. A control unit display section (digital display and air flow indicator) is utilized for self-diagnosing each sensor and actuator. A proportional integral control system is used within the temperature control system and provides quick and accurate response without generation of steady-state error during stabilized operation.