Chevrolet Equinox Service Manual: Manual HVAC Description and Operation

The air temperature and the air delivery description andoperation are divided into eight areas:

HVAC Control ComponentsAir SpeedAir DeliveryHeating and A/C OperationRecirculation OperationEngine CoolantA/C CycleHVAC Control Components

Radio/HVAC Control

The Radio/HVAC control contains all switches, which arerequired to control the functions of HVAC and serve as interfacebetween the operator and the HVAC control module. The selectedvalues are passed to the HVAC control module via LIN-Bus.

HVAC Control Module

The HVAC control module is a GMLAN device that interfacesbetween the operator and the HVAC system to maintain and controldesired air temperature and air distribution settings. The batterypositive voltage circuit provides power that the HVAC controlmodule uses for keep alive memory. If the battery positive voltagecircuit loses power, all HVAC DTCs and settings will be erased fromkeep alive memory. The body control module (BCM), which is thevehicle mode master, provides a device ON-Signal. The HVAC controlmodule provides blower, air delivery mode and air temperaturesettings.

The HVAC control module supports the followingfeatures:

Feature

Availability

Afterblow	Available if reprogrammed by the technician
Purge	Yes
Personalization	Yes
Actuator Calibration	Yes

Mode Actuator

The actuator is a 5-wire bi-directional electric motor thatincorporates a feedback potentiometer. Low reference, 5V reference,position signal, and 2 control circuits enable the actuator tooperate. The control circuits use either a 0 or 12-Vvalue to coordinate the actuator movement. When the actuator is atrest, both control circuits have a value of 0-V. Inorder to move the actuator, the HVAC control module grounds one ofthe control circuits while providing the other with12-V. The HVAC control module reverses the polarity ofthe control circuits to move the actuator in the oppositedirection. When the actuator shaft rotates, the potentiometersadjustable contact changes the door position signal between0–5-V. The HVAC control module uses a range of0–255-counts to index the actuator position.The door position signal voltage is converted to a0–255-count range. When the module sets acommanded, or targeted, value, one of the control circuits isgrounded. As the actuator shaft rotates the changing positionsignal is sent to the module. Once the position signal and thecommanded value are the same, the module removes power and groundfrom the control circuits.

Air Temperature Actuator

The actuator is a 5-wire bi-directional electric motor thatincorporates a feedback potentiometer. Low reference, 5V reference,position signal, and 2 control circuits enable the actuator tooperate. The control circuits use either a 0 or 12-Vvalue to coordinate the actuator movement. When the actuator is atrest, both control circuits have a value of 0-V. Inorder to move the actuator, the HVAC control module grounds one ofthe control circuits while providing the other with12-V. The HVAC control module reverses the polarity ofthe control circuits to move the actuator in the oppositedirection. When the actuator shaft rotates, the potentiometersadjustable contact changes the door position signal between0–5-V. The HVAC control module uses a range of0–255-counts to index the actuator position.The door position signal voltage is converted to a0–255-count range. When the module sets acommanded, or targeted, value, one of the control circuits isgrounded. As the actuator shaft rotates the changing positionsignal is sent to the module. Once the position signal and thecommanded value are the same, the module removes power and groundfrom the control circuits.

Recirculation Actuator

The actuator is a 5-wire bi-directional electric motor thatincorporates a feedback potentiometer. Low reference, 5V reference,position signal, and 2 control circuits enable the actuator tooperate. The control circuits use either a 0 or 12-Vvalue to coordinate the actuator movement. When the actuator is atrest, both control circuits have a value of 0-V. Inorder to move the actuator, the HVAC control module grounds one ofthe control circuits while providing the other with12-V. The HVAC control module reverses the polarity ofthe control circuits to move the actuator in the oppositedirection. When the actuator shaft rotates, the potentiometersadjustable contact changes the door position signal between0–5-V. The HVAC control module uses a range of0–255-counts to index the actuator position.The door position signal voltage is converted to a0–255-count range. When the module sets acommanded, or targeted, value, one of the control circuits isgrounded. As the actuator shaft rotates the changing positionsignal is sent to the module. Once the position signal and thecommanded value are the same, the module removes power and groundfrom the control circuits.

Blower Motor Control Processor

The blower motor control processor controls the speed of theblower motor by increasing or decreasing the voltage drop on theground side of the blower motor. The HVAC control module provides alow side pulse width modulation (PWM) signal to the blower motorcontrol processor via the blower motor speed control circuit. Asthe requested blower speed increases, the HVAC control moduleincreases the amount of time that the speed signal is modulated toground. As the requested blower speed decreases, the HVAC controlmodule decreases the amount of time that the signal is modulated toground.

Evaporator Temperature Sensor

The evaporator temperature sensor is a 2-wire negativetemperature co-efficient thermistor. The sensor operates within atemperature range of −40 to +85°C (−40to +185°F). The sensor is installed at the evaporator andmeasures its temperature. If the temperature drops under3°C (38°F), the compressor will be switched off inorder to prevent a frozen evaporator.

A/C Refrigerant Pressure Sensor

The A/C refrigerant pressure sensor is a 3-wire piezoelectricpressure transducer. A 5-V reference voltage, lowreference, and signal circuits enable the sensor to operate. TheA/C pressure signal can be between 0.2–4.8-V.When the A/C refrigerant pressure is low, the signal value is near0-V. When the A/C refrigerant pressure is high, thesignal value is near 5-V. The engine control module(ECM) converts the voltage signal to a pressure value. Whenpressure is too high or too low, the ECM will not allow the A/Ccompressor clutch to engage.

A/C Compressor

The A/C compressor is belt driven and operates when themagnetic clutch is engaged. When the A/C switch is pressed, theHVAC control module sends an A/C request message to the ECM viaCAN-Bus. Therefore the ECM grounds the A/C compressor clutch relaycontrol circuit, which will switch the A/C compressor clutch relay.With the relay contacts closed, battery voltage is supplied to theA/C compressor clutch. The A/C compressor clutch will beactivated.

Air Speed

The blower control switch is part of the Radio/HVAC control.The selected value of the blower switch position is sent to theHVAC control module via LIN-Bus.

The blower motor control module is an interface between HVACcontrol module and blower motor. The blower motor control moduleregulates supply voltage and ground circuits to blower motor. TheHVAC control module provides a PWM signal to the blower motorcontrol module in order to command the desired blower motor speed.The blower motor control module supplies battery voltage to theblower motor and uses the blower motor ground as a low side controlto adjust the blower motor speed. The voltage amounts between2–13-V and changes linear to the height of thePWM signal.

Air Delivery

The HVAC control module controls the distribution of air bythe use of recirculation and mode actuator. The modes that may beselected are:

DefrostDefogPanelFloor

The desired air distribution mode can be selected with theair distribution switches at the Radio/HVAC control. The Radio/HVACcontrol delivers the values to the HVAC control module via LIN-Bus.The HVAC control module controls the air distribution actuator sothat it drives the flap to the calculated position. Depending onthe position of the flap, air is distributed through various ductsleading to the outlets in the dash. Turning the mode flap to thedefrost position, the HVAC control module will move therecirculation actuator to outside air, reducing window fogging.When defrost is selected, the blower motor will be activated,regardless of the coolant temperature. The HVAC control moduleenables a high volume of air delivered to the front defrost vents.A/C is available in all modes.

The rear window defogger does not affect the HVACsystem.

Heating and A/C Operation

The purpose of the heating and A/C system is to provideheated and cooled air to the interior of the vehicle. The A/Csystem will also remove humidity from the interior and reducewindshield fogging. Regardless of the temperature setting, thefollowing can affect the rate that the HVAC system can achieve thedesired temperature:

Recirculation actuator settingDifference between inside and desired temperatureBlower motor speed settingMode setting

Pressing the A/C switch enables the HVAC control module torequest A/C compressor engagement and turn ON the A/C switch LED.The HVAC control module sends a message to the engine controlmodule (ECM) for A/C compressor engagement. The ECM will provide aground for the A/C compressor relay enabling it to close itsinternal contacts to send battery voltage to the A/C compressorclutch coil. The A/C compressor diode will prevent a voltage peak,resulting from the collapse of the magnetic field of the coil, fromentering the vehicle electrical system when the compressor isdisengaged.

The following conditions must be met in order to activate theA/C compressor:

Battery voltage is between 9–18-VEngine coolant temperature is less than 124°C(255°F)Engine speed is greater than 600-RPMEngine speed is less than5-500-RPMA/C high side pressure is between269–2-929-kPa(39–425-PSI)Throttle position is less than 100%Evaporator temperature is greater than 3°C(38°F)ECM does not detect immoderate torque loadECM does not detect insufficient idle qualityThe ambient temperature is above 1°C(34°F)

The sensor information is used by the ECM to determine thefollowing:

The A/C high side pressureAn A/C system load on the engineAn immoderate A/C high side pressureThe heat load at the A/C condenser

The air streams into the passenger compartment through theheater core and the evaporator core. The air temperature actuatordrives the mixed air flap to induce the airflow. If the interiortemperature should be increased, the mixed air flap is put into theposition in which more air streams through the heater core. If theinterior temperature should be decreased, the mixed air flap is putinto the position in which more air streams through the evaporatorcore.

Recirculation Operation

The recirculation switch and the fresh air switch are part ofthe Radio/HVAC control. The selected switch position is sent to theHVAC control module via LIN-Bus. The HVAC control module controlsthe air intake through the recirculation actuator. Therecirculation switch closes the recirculation flap in order tocirculate the air within the vehicle. Through selection of thefresh air switch, the recirculation flap is opened again in orderto route outside air into the vehicle.

Recirculation is only available if the defrost mode is notactive. When the defrost mode is active, the recirculation actuatoropens the recirculation flap and outside air is circulated to thewindshield to reduce fogging.

Engine Coolant

Engine coolant is the essential element of the heatingsystem. The thermostat controls the normal engine operating coolanttemperature. The thermostat also creates a restriction for thecooling system that promotes a positive coolant flow and helpsprevent cavitation.

Coolant enters the heater core through the inlet heater hose,in a pressurized state. The heater core is located inside the HVACcontrol module. The ambient air drawn through the HVAC controlmodule absorbs the heat of the coolant flowing through the heatercore. Heated air is distributed to the passenger compartment,through the HVAC control module, for passenger comfort. Opening orclosing the air temperature flap controls the amount of heatdelivered to the passenger compartment. The coolant exits theheater core through the return heater hose and recirculates back tothe engine cooling system.

A/C Cycle

Refrigerant is the key element in an air conditioning system.R-134a is presently the only Environmental Protection Agencyapproved refrigerant for automotive use. R-134a is a very lowtemperature gas that can transfer the undesirable heat and moisturefrom the passenger compartment to the outside air.

The compressor builds pressure on the vapor refrigerant.Compressing the refrigerant also adds heat to the refrigerant. Therefrigerant is discharged from the compressor, through thedischarge hose, and forced to flow to the condenser and thenthrough the balance of the A/C system. The A/C system ismechanically protected with the use of a high pressure reliefvalve. If the A/C refrigerant pressure sensor fails or if therefrigerant system becomes restricted and refrigerant pressurecontinued to rise, the high pressure relief will pop open andrelease refrigerant from the system.

Compressed refrigerant enters the condenser in a hightemperature, high pressure vapor state. As the refrigerant flowsthrough the condenser, the heat of the refrigerant is transferredto the ambient air passing through the condenser. Cooling therefrigerant causes the refrigerant to condense and change from avapor to a liquid state.

The condenser is located in front of the radiator for maximumheat transfer. The condenser is made of aluminum tubing andaluminum cooling fins, which allows rapid heat transfer for therefrigerant. The semi-cooled liquid refrigerant exits the condenserand flows to the Receiver/Dehydrator (R/D).

The R/D contains desiccant that absorbs moisture that may bein the refrigerant system. The R/D also acts as a storage vessel toensure that a steady flow of liquid reaches the thermal expansionvalve. The refrigerant exits the R/D and flows through the liquidline to the thermal expansion valve.

The thermal expansion valve is located at the front of dashand attaches to the evaporator inlet and outlet pipes. The thermalexpansion valve is the dividing point for the high and the lowpressure sides of the A/C system. As the refrigerant passes throughthe thermal expansion valve, the pressure on the refrigerant islowered. The thermal expansion valve also meters the amount ofliquid refrigerant that can flow into the evaporator.

Refrigerant exiting the thermal expansion valve flows intothe evaporator core in a low pressure, liquid state. Ambient air isdrawn through the HVAC control module and passes through theevaporator core. Warm and moist air will cause the liquidrefrigerant boil inside of the evaporator core. The boilingrefrigerant absorbs heat from the ambient air and draws moistureonto the evaporator. The refrigerant exits the evaporator throughthe suction line and back to the A/C compressor, in a vapor state,and completing the A/C cycle of heat removal. At the A/Ccompressor, the refrigerant is compressed again and the cycle ofheat removal is repeated.

The conditioned air is distributed through the HVAC controlmodule for passenger comfort. The heat and moisture removed fromthe passenger compartment will also change form, or condense, andis discharged from the HVAC control module as water.