Workshop Repair and Service Manuals GMC SIERRA
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Air Temperature Description and Operation - part 4

Rating:
This value will not be displayedon the scan tool. The default action ensures that the HVAC system can adjust the insideair temperature near the desired temperature until the condition is fixed. The scantool parameter for the sunload sensor is the actual state of the signal circuit.

A/C Refrigerant Pressure Sensor

The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer.A 5-volt reference, low reference, and signal circuits enable the sensor to operate.The A/C pressure signal can be between 0–5-volts. When the A/C refrigerant pressureis low, the signal value is near 0-volts. When the A/C refrigerant pressure is high,the signal value is near 5-volts. The powertrain control module (PCM) converts thevoltage signal to a pressure value.

The A/C refrigerant pressure sensor protects the A/C system from operating when anexcessively high pressure condition exists. The PCM disables the compressor clutchif the A/C pressure is more than 2957-kPa (429-psi). The clutch will be enabled afterthe pressure decreases to less than 1578-kPa (229-psi).

Heating and A/C Operation

The purpose of the heating and A/C system is to provide heated and cooled air to theinterior of the vehicle. The A/C system will also remove humidity from the interiorand reduce windshield fogging. The vehicle operator can determine the passenger compartmenttemperature by adjusting the air temperature switch. The vehicle passenger can offsetthe passenger temperature as much as 16.7°C (30°F). Regardless of the temperaturesetting,the following can affect the rate that the HVAC system can achieve the desired temperature:

Recirculation actuator settingDifference between inside and desired temperatureDifference between ambient and desired temperatureBlower motor speed settingMode settingAuxiliary HVAC settings

The control module makes the following actions when automatic operation is not selected,and an air temperature setting is selected:

When the air temperature switch is placed in the warmest position, the control modulecommands the air temperature door to divert maximum air past the heater core.When the air temperature switch is placed in the coldest position, the control modulecommands the air temperature door to direct air to bypass the heater core.

When the air temperature switch is placed between the warmest and coldest positions,the control module monitors the following sensor inputs to determine the air temperaturedoor position that diverts the appropriate amount of air past the heater core in orderto achieve the desired temperature:

SunloadDuct temperaturesAmbient temperatureInside temperature

The A/C system can be engaged by either pressing the A/C switch or during automaticoperation. The HVAC control module sends a GMLAN message to the powertrain controlmodule (PCM) for A/C compressor engagement. The PCM will provide a ground for theA/C compressor relay enabling it to close its internal contacts to send battery voltageto the A/C compressor clutch coil. The A/C compressor diode will prevent a voltagespike, resulting fromthe collapse of the magnetic field of the coil, from entering the vehicle electricalsystem when the compressor is disengaged.

Air Delivery Description and Operation - part 5     Inside Air Temperature SensorAmbient Air Temperature SensorLower Left Air Temperature SensorLower Right Air Temperature SensorUpper Left Air Temperature SensorUpper Right Air Temperature SensorRegulate blower motor...
Air Delivery Description and Operation - part 3     The blower motor control module is an interface between theHVAC control module and the blower motor. The blower motor speedcontrol, battery positive and ground circuits enable the controlmodule to operate. The HVAC control...
Air Temperature Description and Operation - part 3     The ambient air temperature is less than 4°C (40°F).The evaporator temperature is less than 3°C (38°F).The throttle position is 100%.The A/C high side pressure is more than 2957-kPa (429-psi).The engine coolant temperature...
Air Temperature Description and Operation - part 5     The following conditions must be met in order for the A/C compressor clutch to turnON if they are not all met and an A/C request is made the LED on the A/C switch willflash: Ambient air temperature above 7°C (45°F)The...
Fastener Tightening Specifications - 4WD Driveline Control     Fastener Tightening Specifications Application Specification Metric English Auxiliary Air Temperature Actuator Screws 1.6-Y 14-lb-in Auxiliary Blower Motor Processor Screws 1.6-Y 14-lb-in...
Air Delivery Description and Operation - part 4     The motor moves the mode door tothe desired position. Front Defrost When defrost is selected, the A/C compressor is activated.The A/C compressor clutch will engage when ambient temperatures areabove 3°C (38 F). The blower...