Sensor Inputs

SENSOR INPUTS
Five temperature inputs and one solar input are monitored by the Air Conditioning Programmer (ACP) for the climate control system. Thermistors are used to measure temperatures by decreasing in resistance as temperature increases. Each of the thermistor type sensors and solar sensor is described below:

INSIDE AIR TEMPERATURE SENSOR





The inside air temperature sensor is located in the Instrument Panel (I/P) to the left of center. To provide interior air temperature sensing, a small amount of air is drawn into the sensor housing and passed over the thermistor. The air movement is accomplished by using an aspirator mounted on the top of the HVAC module. Air flow from the HVAC module creates a slight vacuum at one end of the aspirator which draws inside air through the sensor housing and over the thermistor.

OUTSIDE TEMPERATURE SENSOR
This sensor is located in front of the radiator. The sensor data is processed by the ACP and displayed on the Climate Control Center (CCC).

During periods of city traffic and idle conditions, engine heat can surround the area of the outside temperature sensor and cause temperature readings that are higher than the actual outside air temperature. To help eliminate these "false" readings, programming techniques are used to minimize unwanted temperature variations.

A temperature "memory" feature is used in the ACP outside temperature programming to help provide greater accuracy under engine restart conditions. If engine coolant temperature is less than 10°C (18°F) above the outside temperature sensor reading, the actual sensed outside temperature is displayed. However, if engine coolant is greater than 10°C (18°F) above the sensor reading, "memorized" outside temperature is displayed. This is the displayed temperature sensed when the engine was previously operating. At car speeds greater than 20 mph, the outside temperature display may be allowed to increase, but only after a built-in 80 second time delay which allows for outside air to cool the sensor. The 80 second time delay starts when vehicle speed reaches or maintains at least 20 mph. If the sensor reading is ever less than the displayed value or if the vehicle speed is 45 mph or greater, there is no delay and outside temperature changes are displayed as rapidly as possible.

COOLANT TEMPERATURE SENSOR
The coolant temperature sensor is located in a coolant passage of the intake manifold. Sensor resistance is monitored by the PCM which in turn sends the coolant temperature value to the ACP over the data circuit.

A/C HIGH SIDE TEMPERATURE SENSOR
The high side sensor is located in the high pressure refrigerant liquid line between the condenser and orifice tube. The Air Conditioning Programmer (ACP) monitors the refrigerant temperature and transfers that data to the PCM to use in conjunction with the coolant temperature to determine the need for cooling fans, and to prevent the A/C compressor from operating at high discharge pressures.

A/C LOW SIDE TEMPERATURE SENSOR
The low side sensor is located in the low pressure refrigerant line between the orifice tube and evaporator. The Air Conditioning Programmer (ACP) monitors this sensor to determine the low side pressure based on the pressure/temperature relationships of R-134a.

SOLAR SENSOR
The solar sensor uses a light sensitive photocell to control the signal voltage to the ACE The Air Conditioning Programmer (ACP) will see a low voltage in direct light and a higher voltage in shaded conditions.