Workshop Repair and Service Manuals GMC SIERRA
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Air Temperature Description and Operation - part 6

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To place the auxiliary HVAC system in Automatic mode, the following is required:

The auxiliary blower motor switch on the auxiliary HVAC control assembly must be inthe Auto position.The auxiliary mode switch on the auxiliary HVAC control assembly must be in the Autoposition.The auxiliary air temperature switch must be in any other position other than fullhot or full cold position.

Once the desired temperature is reached, the auxiliary blower motor, auxiliary modeand auxiliary temperature actuator will automatically be adjusted to maintain thetemperature selected. The auxiliary HVAC control module performs the following functionsto maintain the desired air temperature:

Upper Air Temperature Sensor – AuxiliaryLower Air Temperature Sensor – AuxiliaryRegulate auxiliary blower motor speedPosition the auxiliary air temperature actuatorPosition the auxiliary mode actuator

Engine Coolant

Engine coolant is the essential element of the heating system. The thermostat controlsthe normal engine operating coolant temperature. The thermostat also creates a restrictionfor the cooling system that promotes a positive coolant flow and helps prevent cavitation.Coolant enters the heater core through the inlet heater hose, in a pressurized state.The heater core is located inside the HVAC module. The ambient air drawn through theHVAC module absorbs the heat of the coolant flowing through the heater core. Heatedair is distributed to the passenger compartment, through the HVAC module, for passengercomfort. Opening or closing the air temperature door controls the amount of heat deliveredto the passenger compartment. The coolant exits the heater core through the returnheater hose and recirculated back through the engine cooling system.

Remote Start

Remote Start Activation

The following describes the HVAC control head functionality upon receiving the remotestart active serial data message and a power mode status is set to off/awake. Theoutside air temperature (OAT) sensor on automatic systems, is utilized to determinethe moding of the following features: Blower Mode, Bi-level, Floor, Defrost, Recircand Rear Defrost. Calibratable temperatures are utilized to provide low, mid and hightemperature rangesfor the selectable feature . Blower and mode have the range to select any valid featurepositions. When the remote start active serial data is received, ignition-OFF loopHVAC algorithms will act the same as if a run power mode was received, i.e. re-calibration,afterblow, ignition-OFF motor positioning etc. The OFF timer and the ignition ON timerhave the functionality as in the Run mode.

The remote start system operates in one of three zones of operation:

Cold ambient temperature that is below 5°C (41°F)Hot ambient temperature that is above 30°C (86°F)Mid ambient temperature that is anything between the cold and hot valuesIn cold ambient, the system uses 74°F setpoint , auto blower, defrost mode, rear defrostand/or heated mirrors on, heated seats on, rear in mimic.In mid ambient, the system uses 74°F setpoint, auto blower, auto mode, rear in mimic.In hot ambient, the system uses 74°F setpoint in 2007, in 2008 and beyond a 60°F setpointwill be used, auto blower, auto mode, rear in mimic.

Remote Start De-activation

When the remote start is exited, GMLAN power mode equals run mode or remote startengine. In the case of automatic settings, the displays will revert to the actualstate of operation of the features, on the basis of their normal control algorithms.

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