Controls

Automatic Heater A/C Control:

Blower Motor Controller Module Duty Cycles:

The automatic A/C control, uses short-travel, soft-touch buttons for selecting the mode, temperature and blower speeds manually, if desired. In the automatic mode, the desired temperature is set by the driver and a microprocessor utilizes this information along with the two air temperature sensor inputs and a solar sensor input, to provide the desired comfort level. The driver can override the automatic system by selecting mode or blower. The HVAC system will operate in manual mode only.

The microprocessor also provides for system self-tests which result in diagnostic codes being displayed. Faults in the inside and outside temperature sensor circuits and temperature valve control circuit are identified when the control is set to the diagnostic mode.

Basic control operation is shown in the first illustration.

BLOWER MOTOR CONTROLLER MODULE

The blower motor controller module contains solid state circuitry which utilizes a pulse width voltage signal (at a given duty cycle), from the control head and returns an inverse pulse width signal to the blower motor, see the second illustration. The control head pulse width signal is based on the user set temperature, outside air temperature, in vehicle temperature and solar sensor. For example, if the in vehicle temperature is much colder or hotter than the user set temperature, and the "AUTO" button has been selected, the blower motor controller module will control the blower from a high speed to a low speed as the difference in set temperature and in vehicle temperature decreases.

TEMPERATURE SENSORS

Automatic control of in-vehicle temperatures depends on the functioning of an in-vehicle sensor and an outside air sensor. Both sensors are temperature sensitive thermistors whose resistance varies inversely to the temperature. The resistance value determines the signal level which is sent to the heater A/C control. In turn, the heater A/C control microprocessor utilizes this information to develop command signals for the vacuum solenoid module, temperature motor actuator and blower motor pulse width module.

A hose duct connects the in-vehicle sensor housing to an aspirator, and air flow from the HVAC module creates a slight vacuum at the aspirator end of the hose. This vacuum draws in-vehicle air over the in vehicle sensor and improves the accuracy of the sensor's ability to predict cabin temperature.

SUN LOAD TEMPERATURE SENSOR

he sun load temperature sensor is located on a removable grille in the center of the I/P upper trim pad. This sensor measures the amount of heat generated from the sun shining in the vehicle.

VACUUM ELECTRIC SOLENOID

The vacuum solenoid module converts electrical signals from the heater A/C control microprocessor into vacuum commands which position the mode, A/C-defrost, and outside air valves in the air distributor. Vacuum is constantly applied to the module which distributes the vacuum to five solenoid-controlled valves on the module. When the heater A/C control signals the module to change an air distributor valve position, the associated solenoid energizes and vacuum is applied to the proper actuator.

TEMPERATURE VALVE ELECTRIC ACTUATORS

The system also utilizes two bi-directional DC mode valve actuators. The actuators operate on signals from the A/C control that are inputs from the in-vehicle, outside air temperature, solar sensor, and the set temperature. As the actuators turn they move the temperature valves in the HVAC module to obtain the correct blend of heated air from the heater and cooled air from the A/C evaporator.

COMPRESSOR CONTROLS

Compressor control relays, switches and transducers are similar to those in the manual HVAC system described in "Compressor Repair Procedures".