Hummer H1 (2006+). Manual - part 324

11-30 Heating/Ventilation/Air Conditioning (HVAC)

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BLOWER MOTOR RESISTOR REPLACEMENT

Removal

1.

Remove the right side crash pad.

2.

Unplug the blower motor resister connector.

3.

Remove the two screws securing the resister to the HVAC unit and remove the resister (Figure  11-17).

Installation

1.

Secure the resistor to the HVAC unit with the screws. 

2.

Plug the HVAC harness connector into the resistor.

3.

Check the blower motor operation.

4.

Install the right side crash pad.

Figure 11-17:   Blower Motor Resistor Replacement

HIGH PRESSURE CUTOFF SWITCH

The high pressure cutoff switch is located in the rear of the compressor. The switch is wired in series with the compressor clutch
and exposed to high side pressure in the compressor. Should pressure exceed the switch setting, current will be interrupted to the
compressor clutch until the pressure drops to safe levels, then the switch will close allowing the clutch to engage.

Service

The high pressure cutoff switch is serviced as an assembly with the A/C compressor.

BLOWER

MOTOR

RESISTER

HVAC

UNIT

BLOWER

MOTOR

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 Heating/Ventilation/Air Conditioning (HVAC)  11-31

HVAC CONTROLS

Figure 11-18:   HVAC Control Panel

The HVAC system is operated using a control panel. The panel has controls for:

• Blower speed

• Air temperature

• Mode

• Air conditioning

Status for all of the controls is shown using painted marks on the faceplate of the control panel. Operation is based on driver input,
no automatic function is incorporated. Controls for the HVAC system are based on (vacuum) door motors and water valve controls
and (electric) blower motor and temperature door motor controls (Figure  11-18).

Blower Speed Dial

The blower speed dial has 4 positions. 

• Low

• Med 1

• Med 2

• High

The operator selects the fan speed by rotating the dial clockwise (Figure  11-19).

Figure 11-19:   Blower Speed Dial

Temperature Dial

The temperature dial controls the temperature of the air exiting the HVAC unit. When the dial is rotated to the cold position, the
water valve is shut off and the temperature door isolates the heater core. When the dial is rotated to the HOT position, the water
valve opens and the temperature blend door directs air through the heater core. Between COLD and HOT, temperature is regulated
by changing the amount of air that passes through the heater core (Figure  11-20).

HVAC CONTROL HEAD

7-S11-073

7-S11-073

11-32 Heating/Ventilation/Air Conditioning (HVAC)

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Figure 11-20:   Temperature Control Dial

Mode Dial

The mode dial allows the operator to direct air to a selected area. When the driver rotates the dial clockwise and chooses a mode,
vacuum is sent to the vacuum motors that must close (Figure  11-21).

NOTE: When the main HVAC unit is without vacuum, air will be directed to the defrost and floor vents and fresh air will be used.
The blower motor on the HVAC unit will not function if the mode dial is set to the OFF position. When the dial is positioned in an
A/C mode, the compressor clutch will be activated.

Figure 11-21:   Mode Dial

HVAC UNIT SERVICE

WARNING:  When working with refrigerant, always use protective equipment to prevent injury. Refrigerant han-
dling should be done only by technicians trained and certified in the use of refrigerant and refrigerant service
equipment.

CAUTION: Use only equipment and materials designed to operate with R134a refrigerant. Never substitute parts or materials de-
signed for R12.

CAUTION: Never use sealers in or on the HVAC unit that are not designed for ventilation systems. Some sealers release noxious
or irritating odors that will be offensive to operators of the vehicle. Neutral cure sealers should be used when sealing any area of
the HVAC unit that could potentially expose the operator of the vehicle or the passengers to the released chemicals.

7-S11-073

7-S11-073

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 Heating/Ventilation/Air Conditioning (HVAC)  11-33

MAIN HVAC UNIT

The main HVAC unit is comprised of a heater core for heating air, an evaporator for cooling air, mode doors to direct airflow and
an electric blower motor/ fan to force air through the case to be heated or cooled (Figure  11-22).

Figure 11-22:   Main HVAC Unit

Diverter Doors

Three diverter doors occupy the outlet area of the main unit. Various positions and combinations of three doors provide the system
with the following mode selections:

• Off

• Maximum A/C - Recirculate

• A/C

• A/C Face/Floor blend

• Face

• Floor

• Defrost

All four of the mode doors are operated using vacuum motors mounted externally to the case (Figure  11-23). The motors are as
follows:

• Floor door motor

• Defrost block-off motor

• Face door motor

• Recirculate door motor

The vacuum motors are capable of two positions: fully extended (spring pressure) or fully retracted (vacuum). The face door motor
is an exception, having a third position in the center of travel. A second vacuum inlet is added to the face door motor for this pur-
pose (Figure  11-23).

FACE OUTLET

DRAIN TUBE

MAIN HVAC UNIT

VACUUM

MOTOR

COVER

BLOWER

MOTOR

RESISTER