Hummer H1 (2006+). Manual — part 325

11-34 Heating/Ventilation/Air Conditioning (HVAC)

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The temperature blend door motor operates the temperature blend door. This door is responsible for regulating outlet air tempera-
ture by directing air through the heater core or by blocking air to the core. The temperature blend door motor is electric and can be
positioned at multiple points.

Figure 11-23: Vacuum Door Motors

TEMPERATURE BLEND DOOR

FACE DOOR MOTOR

FLOOR DOOR MOTOR

RECIRCULATE DOOR MOTOR

BLOCK-OFF

MOTOR

DEFROST

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Heating/Ventilation/Air Conditioning (HVAC) 11-35

Heater Core

The heater core is composed of aluminum with numerous passages allowing heated engine coolant to pass through, transferring
heat into the passing air from the blower motor. Coolant flow through the heater core is controlled by the water control valve in the
engine compartment (Figure 11-24).

Figure 11-24: Heater Core

HEATER CORE

RETAINING BRACKET

HVAC CASE HALF

(FRONT)

11-36 Heating/Ventilation/Air Conditioning (HVAC)

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Evaporator

The evaporator is composed of a wide flat aluminum tube bent in a serpentine pattern. Fins extending out from the tube assist in
transferring heat from the passing air into the refrigerant which is evaporating inside of the tubes (Figure 11-25).

Figure 11-25: Evaporator

Thermostatic Cycling Switch

The thermostatic cycling switch is mounted on the side of the main HVAC unit (Figure 11-25). The thermostatic cycling switch is
responsible for turning off the compressor clutch when evaporator temperature approaches freezing. Temperature is sensed by a
capillary tube inserted in the fins of the evaporator. Should the evaporator reach freezing temperatures, moisture condensing on the
fins of the evaporator will freeze and hinder air flow. The thermostatic cycling switch will interrupt current to the compressor
clutch until the temperature rises to about 40° F.

Expansion Valve

The expansion valve controls the flow of refrigerant through the evaporator. Refrigerant must be metered to prevent the liquid re-
frigerant from flooding the evaporator. The expansion valve is exposed to both low and high pressures and bases refrigerant flow
on the pressure which is exiting the evaporator (Figure 11-26).

Figure 11-26: Expansion Valve

EVAPORATOR

HVAC CASE HALF (REAR)

THERMOSTATIC

CYCLING

SWITCH

INLET

OUTLET

EXPANSION VALVE

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Heating/Ventilation/Air Conditioning (HVAC) 11-37

Blower Motor

The blower motor is a permanent magnet electric motor that drives a wheel type fan (Figure 11-27). The air enters the unit from
the outside air intake or from a door on the interior of the vehicle. The air is then forced through the evaporator and heater core.

Figure 11-27: Blower Motor and Housing

MAIN UNIT REPLACEMENT

Removal

1.

Drain the Coolant into an approved container.

2.

Recover the refrigerant.

3.

Remove the rain cap and the adapter.

4.

Remove the air intake elbow, air cleaner and the splash shield.

5.

Remove the four bolts securing the heater core extension tubes to the passthrough plate. Plug all open holes and discard all the
sealing washers (Figure 11-28).

Figure 11-28: Passthrough Fastener Removal

6.

Remove any pliable sealer from the exterior of the passthrough plate.

7.

Remove the center console.

8.

Remove the right side crash pad.

BLOWER MOTOR

BLOWER HOUSING

7-P11-003.1

MANIFOLD

BLOCK

HEATER CORE

EXTENSION TUBE

HEATER CORE

EXTENSION TUBE

PASS-

THROUGH

MOUNT

BOLTS