Hummer H2. Manual - part 1959

Fig. 39: Sun Load Sensor & I/P Upper Trim Pad 
Courtesy of GENERAL MOTORS CORP. 

1. Remove the I/P upper trim pad. Refer to Trim Pad Replacement - Instrument Panel (I/P) Upper in 

Trim Pad Replacement-I/P Upper.  

2. Remove the sun load sensor from the I/P upper trim pad by turning counter clockwise.  

3. Disconnect the electrical connector from the sun load sensor.  

Installation Procedure 

 

2004 Hummer H2 

2004 HVAC HVAC Systems - Automatic - Hummer H2

  

Fig. 40: Sun Load Sensor & I/P Upper Trim Pad 
Courtesy of GENERAL MOTORS CORP. 

1. Connect the electrical connector to the sun load sensor.  

2. Install the sun load sensor to the I/P upper trim pad by turning clockwise.  

3. Install the I/P upper trim pad. Refer to Trim Pad Replacement - Instrument Panel (I/P) Upper .  

DESCRIPTION AND OPERATION

 

2004 Hummer H2 

2004 HVAC HVAC Systems - Automatic - Hummer H2

  

AIR DELIVERY DESCRIPTION AND OPERATION

The air delivery description and operation is divided into 5 areas: 

z

HVAC Control Components  

z

Air Speed  

z

Air Delivery  

z

Recirculation Operation  

z

Automatic Operation  

HVAC Control Components 

HVAC Control Module 

The HVAC control module is a class 2 device that interfaces between the operator and the HVAC system to 
maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the 
control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all 
HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle 
mode master, provides a device on signal. The control module supports the following features: 

Air Delivery Description and Operation 

Mode Actuator 

The mode actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 
3 voltage, low reference, control, 5-volt reference and position signal circuits enable the actuator to operate. The 
control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at 
rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the actuator movement in 
opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door 
position signal between 0-5 volts. 

The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal 
voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control 
signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the 
commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the 
position signal and the commanded value are the same, the module changes the control signal to 2.5 volts. 

Blower Motor Control Processor 

The blower motor control processor controls the speed of the blower motor by increasing or decreasing the 

Feature

Availability

Afterblow

No

Purge

No

Personalization

Yes

Actuator Calibration

Yes

 

2004 Hummer H2 

2004 HVAC HVAC Systems - Automatic - Hummer H2

  

voltage drop on the ground side of the blower motor. The HVAC control module provides a linear pulse 
modulated signal to the blower motor control processor over the blower motor speed control circuit. As the 
requested blower speed increases, the HVAC control module increases the amount of time that the speed signal 
is modulated to ground. As the requested blower speed decreases, the HVAC control module decreases the 
amount of time that the signal is modulated to ground. 

Air Speed - Front Control 

The blower control switch is integrated into the HVAC control module. The two rocker type switches provide 
the vehicle operator the ability to select several blower speeds. The HVAC control module uses a bar graph type 
display to indicate the selected blower speed. The HVAC control module provides a linear pulse modulated 
(LPM) signal to the blower motor through the blower motor speed control circuit. The blower motor changes 
speed based on the received LPM signal from the HVAC control module. Power and ground are provided to the 
blower motor through the battery positive voltage and ground circuits. When the HVAC control module is 
operating in AUTO mode, the system automatically controls the blower speed. Power and ground are provided 
to the HVAC control module by the ignition 3 voltage and the ground circuits. 

Air Distribution 

The HVAC control module controls the distribution of air by the use of a mode actuator. The modes that may 
be selected are: 

z

Defrost  

z

Defog  

z

Panel  

z

BI-Level  

z

Floor  

Mode Actuator 

The mode actuator is connected to the mode door by a cam type linkage system. Depending on the position of 
the door, air is directed through the HVAC module and distributed through various ducts leading to the outlets 
in the dash. If the HVAC control module detects a fault with the mode door the HVAC control module will try 
to drive the actuator for a predetermined amount of time, to defrost, which is the defaulted position for the mode 
door actuator. When the mode switch is placed in the defrost or defog positions the A/C is commanded ON and 
the recirculation door is moved to the outside air position to help reduce window fogging. A/C is available in all 
modes and recirculation is only available in the panel and bi-level modes. 

Front Defrost 

When defrost is selected, the A/C compressor is activated. The A/C compressor clutch will engage when 
ambient temperatures are above 3° C (38° F). The blower motor will be activated, regardless of the coolant 
temperature. The HVAC control module will override the auxiliary HVAC control module so a high volume of 
air is delivered to the front defrost vents. The rear window defogger does not affect the HVAC system. 

Recirculation Operation 

 

2004 Hummer H2 

2004 HVAC HVAC Systems - Automatic - Hummer H2