Hummer H3. Manual — part 1303

DESCRIPTION AND OPERATION

AIR DELIVERY DESCRIPTION AND OPERATION

The air delivery description and operation is divided into 4 areas:

HVAC Control Components

Air Speed

Air Distribution

Recirculation Operation

HVAC Control Components

HVAC Control Assembly

The HVAC control assembly is a non-class 2 device that interfaces between the operator and the
HVAC system to maintain air temperature and distribution settings. An ignition 3 voltage circuit
provides power to the control assembly. The air temperature, mode and recirculation actuator are
electrically controlled. The control assembly does support the following features:

Air Delivery Description and Operation

2. Remove the air inlet assembly. Refer to Air Inlet Assembly Replacement (Left

Hand Drive) or Air Inlet Assembly Replacement (Right Hand Drive) .

3. Disconnect the recirculation actuator electrical connector.

1

Recirculation Housing Screw (Qty: 4)

Tighten: 1.5 N.m (14 lb in)

NOTE:

Refer to Fastener Notice .

2

Recirculation Housing

3

Recirculation Actuator Screw (Qty: 3)

Tighten: 1.5 N.m (13 lb in)

4

Recirculation Actuator
Procedure:
Recalibrate the Actuator. Refer to Actuator Recalibration.

Feature

Availability

2007 Hummer H3

2007 HVAC HVAC - Manual - H3

Air Speed

The HVAC control assembly applies a ground to the blower motor control circuit that
corresponds to the selected blower speed. The resistors and the blower motor are in a series
circuit. The following list represents the number of resistors in series with the blower motor per
particular speed request:

Low speed, 3 resistors

Medium 1 speed, 2 resistors

Medium 2 speed, 1 resistors

When the operator requests High speed, the HVAC control assembly activates a relay which
applies direct ground to the blower motor.

Air Distribution

Mode Actuator

The mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback
potentiometer. Low reference, control A, control B, 5-volt reference and position signal circuits
enable the actuator to operate. Two control circuits enable the actuator to operate. The control
circuits use either ground or a 12-volt value to coordinate the actuator movement. The HVAC
control assembly reverses the polarity of the control circuits to move the actuator in the opposite
direction. 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 circuits are energized 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 opens the control circuits.

Recirculation Operation

The recirculation actuator is a 2-wire bi-directional electric motor. Two control circuits enable
the actuator to operate. The control circuits use either ground or a 12-volt value to coordinate the

Afterblow

No

Purge

No

Personalization

No

Actuator Calibration

Yes

2007 Hummer H3

2007 HVAC HVAC - Manual - H3

actuator movement. The HVAC control assembly reverses the polarity of the control circuits to
move the actuator in the opposite direction. The recirculation operation can function with blower
motor in either the ON or OFF position. Recirculation is not available in Defrost and Mix-Blend
mode. If an operator requests recirc in defrost or mix blend the recirc LED will flash 3 times and
then turn OFF. The system will remain in fresh air mode.

AIR TEMPERATURE DESCRIPTION AND OPERATION

The air temperature controls are divided into 4 areas:

HVAC Control Components

Heating and A/C Operation

Engine Coolant

A/C Cycle

HVAC Control Components

HVAC Control Assembly

The HVAC control assembly is a non-class 2 device that interfaces between the operator and the
HVAC system to maintain air temperature and distribution settings. An ignition 3 voltage circuit
provides power to the control assembly. The air temperature and mode doors are controlled by
cables. The recirculation actuator is electrically controlled. The control assembly does support
the following features:

Air Temperature Description and Operation

Air Temperature Actuator

The air temperature actuator is a 5-wire bi-directional electric motor that incorporates a feedback
potentiometer. Low reference, control A, control B, 5-volt reference and position signal circuits
enable the actuator to operate. Two control circuits enable the actuator to operate. The control
circuits use either ground or a 12-volt value to coordinate the actuator movement. The HVAC
control assembly reverses the polarity of the control circuits to move the actuator in the opposite
direction. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door

Feature

Availability

Afterblow

No

Purge

No

Personalization

No

Actuator Calibration

Yes

2007 Hummer H3

2007 HVAC HVAC - Manual - H3

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 opens the control circuits.

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 pressure is low, the signal value is near 0
volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts.

The A/C refrigerant pressure sensor protects the A/C system from operating when an excessively
high or low pressure condition exists. The powertrain control module (PCM) disables the
compressor clutch under the following conditions:

A/C pressure is more than 2,951 kPa (428 psi). The clutch will be enabled after the pressure
decreases to less than 2,068 kPa (300 psi). A/C high side pressure is less than 310 kPa (44 psi).
The clutch will be enabled after the A/C high side pressure increases to more than 310 kPa (44
psi).

Evaporator Temperature Sensor

The evaporator temperature sensor will not allow an A/C request to the body control module
(BCM) at temperatures less than 0°C (32°F).

Heating and A/C Operation

The purpose of the heating and A/C system is to provide heated and cooled air to the interior of
the vehicle. The A/C system will also remove humidity from the interior and reduce windshield
fogging. The vehicle operator can determine the passenger compartment temperature by adjusting
the air temperature switch. Regardless of the temperature setting, the following can effect the rate
that the HVAC system can achieve the desired temperature:

Recirculation

Difference between inside and desired temperature

Difference between ambient and desired temperature

2007 Hummer H3

2007 HVAC HVAC - Manual - H3