Control Assembly Description Pontiac
The heating, ventilation
and air conditioning (HVAC) control head uses three knobs and one push button
in order to control the following features:
Temperature Control Knob
The temperature control knob regulates the HVAC system air temperature.
The knob is located in the center of the HVAC control head. A temperature
control cable mechanically links the knob to the temperature valve (door).
| • | Turn the knob toward the driver for heat. |
| • | Turn the knob toward the passenger for air conditioning (A/C). |
Mode Control Knob
The mode control knob is located on the right side of the HVAC control
head. The following are the eight different modes:
OFF
The following actions occur when the knob is in the OFF position:
| • | The blower motor does not operate. |
| • | Electrical power is not supplied to the blower motor. |
| • | An A/C request signal is not sent to the powertrain control module
(PCM). |
| • | A small amount of air is forced into the HVAC module by the forward
movement of the vehicle. The air is discharged through the heater and defrost
outlets. |
MAX
The following actions occur when the knob is in the MAX position:
| • | An A/C request signal is sent to the PCM. |
| • | The blower motor operates in one of four blower motor speed control
settings. |
| • | Air is discharged only from the instrument panel air outlets. |
| • | In order to provide MAX A/C, most of the air entering the HVAC
module is taken from the vehicle interior (re-circulated). This interior air
is cooler than the outside air. MAX is the only setting at which the air
is re-circulated. |
Use the MAX setting when the following conditions exist:
| • | The outside air has an objectionable odor |
A/C
The A/C setting functions the same as the MAX setting, except that only
outside air enters the HVAC module. There may be a slight reduction of blower
noise compared to the MAX setting because the re-circulation valve (door)
is closed.
BI-LEVEL A/C
The following actions occur when the knob is in the BI-LEVEL A/C position:
| • | An A/C request signal is sent to the PCM in order to allow the
blower motor to operate in one of four settings. |
| • | Only outside air enters the HVAC module. |
| • | Air is distributed through the instrument panel outlets and the
floor outlets. |
| • | A small amount of air is distributed to the defrost outlet. |
VENT
The VENT setting does not activate an A/C request signal but allows
the blower motor to operate normally. The VENT setting is one of two economy
settings (other than OFF) in which there is no A/C request signal. Air is
discharged through the instrument panel outlets only.
HEATER
The HEATER setting functions the same as the VENT setting, except that
most of the air is discharged through the floor outlets with a small amount
of air discharged through the defroster outlets. Use the HEATER setting for
cold weather operation unless windshield or side window defogging/defrosting
is required.
DEFROST/BLEND
The following actions occur in the DEFROST/BLEND setting:
| • | The blower motor operates. |
| • | An A/C request signal is sent to the PCM. |
| • | Air is discharged through the defroster and floor air outlets. |
The DEFROST/BLEND setting provides greater passenger comfort than the
DEFROST setting, but it is not as effective in defogging/defrosting the windshield
and side windows.
DEFROST
The DEFROST setting functions the same as the DEFROST/BLEND setting
except that most of the air is discharged through the defroster outlets. A
small amount of air goes through the heater and side windows defoggers.
Blower Motor Speed Control
| • | The blower motor runs in all mode positions except the OFF position
when the ignition switch is in the RUN position. |
| • | The blower motor speed is controlled by a four-position electrical
blower motor speed control switch. The switch is located at the left side
of the control. |
| • | The blower motor speed control switch provides a choice of the
following speeds: |
| • | Power is routed from the HVAC fuse in the fuse block to the mode
control switch. |
| • | The mode control switch breaks the circuit when the switch is
in the OFF position. The switch closes the circuit in all other positions. |
| • | From the mode control switch the circuit goes to the blower motor
speed control switch. |
| • | When the blower motor speed control switch is turned to the LOW
setting, voltage is conducted to the resistor. At the resistor, the voltage
passes through all three resistors and is reduced to provide the low blower
motor speed. |
| • | When the blower switch is in either of the two medium speed positions,
the switch closes. This action sends voltage through one or two of the resistors.
Because the current follows the path of least resistance, the circuit branch
that leads directly to all three resistors becomes ineffective. At this point
the current bypasses either one or two resistors, depending upon which medium
speed position is selected. The reduced resistance increases the current flow
and blower motor speed. |
| • | When the blower motor switch is turned to the HIGH setting, the
action energizes the high blower relay. Power is taken from a separate circuit
that is protected by a fusible link. The separate power circuit is hot at
all times. The circuit has the capacity to handle the current demands of
the blower motor at high speed. |
| • | The circuit to the blower motor is completed to ground at the
instrument panel through the instrument panel wiring harness. |
Control Assembly Description Chevrolet
The heating, ventilation
and air conditioning (HVAC) control head uses three knobs and one push button
in order to control the following features:
Temperature Control Knob
The temperature control knob regulates the HVAC system air temperature.
The knob is located in the center of the HVAC control head. A temperature
control cable mechanically links the knob to the temperature valve (door).
| • | Turn the knob toward the driver for heat. |
| • | Turn the knob toward the passenger for air conditioning (A/C). |
Mode Control Knob
The mode control knob is located on the right side of the HVAC control
head. The following are the eight different modes:
OFF
The following actions occur when the knob is in the OFF position:
| • | The blower motor does not operate. |
| • | Electrical power is not supplied to the blower motor. |
| • | An A/C request signal is not sent to the powertrain control module
(PCM). |
| • | A small amount of air is forced into the HVAC module by the forward
movement of the vehicle. The air is discharged through the heater and defrost
outlets. |
MAX
The following actions occur when the knob is in the MAX position:
| • | An A/C request signal is sent to the PCM. |
| • | The blower motor operates in one of four blower motor speed control
settings. |
| • | Air is discharged only from the instrument panel air outlets. |
| • | In order to provide MAX A/C, most of the air entering the HVAC
module is taken from the vehicle interior (re-circulated). This interior air
is cooler than the outside air. MAX is the only setting at which the air
is re-circulated. |
Use the MAX setting when the following conditions exist:
| • | The outside air has an objectionable odor |
A/C
The A/C setting functions the same as the MAX setting, except that only
outside air enters the HVAC module. There may be a slight reduction of blower
noise compared to the MAX setting because the re-circulation valve (door)
is closed.
BI-LEVEL A/C
The following actions occur when the knob is in the BI-LEVEL A/C position:
| • | An A/C request signal is sent to the PCM in order to allow the
blower motor to operate in one of four settings. |
| • | Only outside air enters the HVAC module. |
| • | Air is distributed through the instrument panel outlets and the
floor outlets. |
| • | A small amount of air is distributed to the defrost outlet. |
VENT
The VENT setting does not activate an A/C request signal but allows
the blower motor to operate normally. The VENT setting is one of two economy
settings (other than OFF) in which there is no A/C request signal. Air is
discharged through the instrument panel outlets only.
HEATER
The HEATER setting functions the same as the VENT setting, except that
most of the air is discharged through the floor outlets with a small amount
of air discharged through the defroster outlets. Use the HEATER setting for
cold weather operation unless windshield or side window defogging/defrosting
is required.
DEFROST/BLEND
The following actions occur in the DEFROST/BLEND setting:
| • | The blower motor operates. |
| • | An A/C request signal is sent to the PCM. |
| • | Air is discharged through the defroster and floor air outlets. |
The DEFROST/BLEND setting provides greater passenger comfort than the
DEFROST setting, but it is not as effective in defogging/defrosting the windshield
and side windows.
DEFROST
The DEFROST setting functions the same as the DEFROST/BLEND setting
except that most of the air is discharged through the defroster outlets. A
small amount of air goes through the heater and side windows defoggers.
Blower Motor Speed Control
| • | The blower motor runs in all mode positions except the OFF position
when the ignition switch is in the RUN position. |
| • | The blower motor speed is controlled by a four-position electrical
blower motor speed control switch. The switch is located at the left side
of the control. |
| • | The blower motor speed control switch provides a choice of the
following speeds: |
| • | Power is routed from the HVAC fuse in the fuse block to the mode
control switch. |
| • | The mode control switch breaks the circuit when the switch is
in the OFF position. The switch closes the circuit in all other positions. |
| • | From the mode control switch the circuit goes to the blower motor
speed control switch. |
| • | When the blower motor speed control switch is turned to the LOW
setting, voltage is conducted to the resistor. At the resistor, the voltage
passes through all three resistors and is reduced to provide the low blower
motor speed. |
| • | When the blower switch is in either of the two medium speed positions,
the switch closes. This action sends voltage through one or two of the resistors.
Because the current follows the path of least resistance, the circuit branch
that leads directly to all three resistors becomes ineffective. At this
point the current bypasses either one or two resistors, depending upon which
medium speed position is selected. The reduced resistance increases the current
flow and blower motor speed. |
| • | When the blower motor switch is turned to the HIGH setting, the
action energizes the high blower relay. Power is taken from a separate circuit
that is protected by a fusible link. The separate power circuit is hot at
all times. The circuit has the capacity to handle the current demands of
the blower motor at high speed. |
| • | The circuit to the blower motor is completed to ground at the
instrument panel through the instrument panel wiring harness. |
