The air temperature controls are divided into three primary areas. The first, Heater Mode, is related to how the heater system responds when a heater mode is selected, and how the HVAC system provides the desired temperature for each setting. The second, A/C Mode, is related to how the A/C system responds when an A/C mode is selected by the vehicle operator, and how the HVAC system provides the desired temperature for each setting. The third, A/C Cycle, describes the complete A/C cycle.
Heater Mode
The purpose of the heater is to supply heat to the interior of the vehicle. The vehicle operator can determine the level of heat by sliding the temperature control, located on the HVAC control module, to any setting. The temperature control can change the vehicle's air temperature regardless of the HVAC mode setting, heater or A/C.
The fuse block provides power to the left air temperature actuator through the ignition 3 voltage circuit. Power and ground are provided to the HVAC control module by the ignition 3 voltage and ground circuits.
When a desired temperature setting is selected, the HVAC control module outputs a voltage signal to the air temperature actuator over the control circuit of the air temperature actuator. A potentiometer inside the HVAC control module varies the voltage value on the control circuit based on the position of the air temperature switch. Based on the voltage value on the control circuit, the actuator positions the air temperature door to a to divert sufficient air around or through the heater core to achieve the desired vehicle temperature. Ground is provided by the ground circuit of the air temperature actuator.
Dual Zone
The HVAC control module has dual sliding temperature switches. The fuse block provides power to the right air temperature actuator through the ignition 3 voltage circuit.
When a desired temperature setting is selected, the HVAC control module outputs a voltage signal to the air temperature actuator over the control circuit of the air temperature actuator. A potentiometer inside the HVAC control module varies the voltage value on the control circuit based on the position of the air temperature switch. Based on the voltage value on the control circuit, the actuator positions the air temperature door to a to divert sufficient air around or through the heater core to achieve the desired vehicle temperature. Ground is provided by the ground circuit of the air temperature actuator.
The dual zone controls allows for maximum temperature offset between the driver and passenger. It is possible to divert maximum airflow around the heater core with one dual zone switch and divert maximum airflow through the heater core with the other dual zone switch. Each air temperature actuator is independent from the other and the passenger side is not limited in the range of temperature offset.
Engine Coolant
Engine coolant is the key element of the heating system. The normal engine operating coolant temperature is controlled by the thermostat. The thermostat also creates a restriction for the cooling system that promotes a positive coolant flow and helps prevent cavitation.
Coolant enters the heater core through the inlet heater hose, in a pressurized state. The heater core is located inside the HVAC assembly. The heat of the coolant flowing through the heater core is absorbed by the ambient air drawn through the HVAC assembly. Heated air is distributed to the passenger compartment, through the HVAC assembly, for passenger comfort. The amount of heat delivered to the passenger compartment is controlled by opening or closing the HVAC assembly temperature door. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.
A/C Mode
The purpose of the air conditioning (A/C) system is to provide cool air and remove humidity from the interior of the vehicle. The vehicle operator can activate the A/C system by pressing the A/C switch. The A/C system can operate regardless of the temperature setting. A/C is available as long as outside air temperature is above 4°C (40°F).
When the vehicle operator presses the A/C switch, voltage is sent to the PCM through the A/C request signal circuit. The PCM will command on the A/C compressor clutch relay. The A/C compressor is on in selected modes, even in cool weather conditions, to help eliminate moisture from fogging the windshield. The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control module. Otherwise, the A/C system may be running without the A/C LED indicator illuminated.
The PCM turns on the A/C compressor by providing a path to ground through the A/C clutch relay control circuit for the A/C compressor clutch relay. Power is provided to the A/C compressor clutch relay from the underhood junction block. Once the relay closes its internal switch, power is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. The A/C compressor clutch diode prevents voltage spikes from entering the vehicle electrical system. The ground circuit provides a path to ground for the compressor and relay. The A/C clutch relay control circuit is grounded internally within the PCM.
A/C Refrigerant Pressure Sensor
The A/C system is protected by the A/C refrigerant pressure sensor. The sensors' output to the PCM is variable and is dependent upon pressure inside the line. A higher pressure results in a higher voltage output. The A/C pressure is constantly monitored in order to allow the A/C compressor clutch to disengage as needed. If line pressures climb above 2979 kPa (432 psi), the PCM will turn off the A/C compressor clutch until the pressure lowers to 1510 kPa (219 psi). If line pressures fall below 186 kPa (27 psi), the PCM will turn off the A/C compressor clutch until the pressure raises to 207 kPa (30 psi).
A 5-volt reference voltage is sent out over the 5-volt reference circuit, from the PCM, to the A/C refrigerant pressure sensor. A voltage signal on the A/C refrigerant pressure sensor signal circuit provides the PCM with a pressure input. Ground for the A/C refrigerant pressure sensor is provided by the low reference circuit.
Recirculation Mode
Recirculation is only available in MAX. When MAX is selected, vacuum is applied to the recirculation actuator. The force of the vacuum overcomes the spring pressure of the spring inside the actuator. This moves the actuator, which is linked to the recirculation door, into recirculation mode. This brings air from inside the vehicle instead of fresh air from the outside.
Air Temperature Actuator
The vehicle operator can determine the level of A/C by sliding the temperature control, located on the HVAC control module, to any setting. The temperature control can change the vehicle's air temperature regardless of the HVAC mode setting, heater or A/C. The fuse block provides power to the left air temperature actuator through the ignition 3 voltage circuit. Power and ground are provided to the HVAC control module by the ignition 3 voltage and ground circuits.
When a desired temperature setting is selected, the HVAC control module outputs a voltage signal to the air temperature actuator over the control circuit of the air temperature actuator. A potentiometer inside the HVAC control module varies the voltage value on the control circuit based on the position of the air temperature switch. Based on the voltage value on the control circuit, the actuator positions the air temperature door to a to divert sufficient air around or through the heater core to achieve the desired vehicle temperature. Ground is provided by the ground circuit of the air temperature actuator.
Dual Zone
The HVAC control module has dual sliding temperature switches. The fuse block provides power to the right air temperature actuator through the ignition 3 voltage circuit.
When a desired temperature setting is selected, the HVAC control module outputs a voltage signal to the air temperature actuator over the control circuit of the air temperature actuator. A potentiometer inside the HVAC control module varies the voltage value on the control circuit based on the position of the air temperature switch. Based on the voltage value on the control circuit, the actuator positions the air temperature door to a to divert sufficient air around or through the heater core to achieve the desired vehicle temperature. Ground is provided by the ground circuit of the air temperature actuator.
The dual zone controls allows for maximum temperature offset between the driver and passenger. It is possible to divert maximum airflow around the heater core with one dual zone switch and divert maximum airflow through the heater core with the other dual zone switch. Each air temperature actuator is independent from the other and the passenger side is not limited in the range of temperature offset.
A/C Cycle
Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automotive use. R-134a is a very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.
The A/C system used on this vehicle is a non-cycling system. Non-cycling A/C systems use a high pressure switch to protect the A/C system from excessive pressure. The high pressure switch will OPEN the electrical signal to the compressor clutch, if the refrigerant pressure becomes excessive. After the high and the low sides of the A/C system pressure equalize, the high pressure switch will CLOSE. This completes the electrical circuit to the compressor clutch. The A/C system is also mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continues to rise, the high pressure relief will pop open and release refrigerant from the system.
The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat. The refrigerant is discharged from the compressor through the discharge hose, and forced through the condenser and then through the balance of the A/C system.
Compressed refrigerant enters the condenser at a high-temperature, high-pressure vapor state. As the refrigerant flows through the condenser, the heat is transferred to the ambient air passing through the condenser. Cooling causes the refrigerant to condense and change from a vapor to a liquid state.
The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line to the orifice tube.
The orifice tube is located in the liquid line between the condenser and the evaporator. The orifice tube is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the orifice tube, the pressure on the refrigerant is lowered, causing the refrigerant to vaporize at the orifice tube. The orifice tube also measures the amount of liquid refrigerant that can flow into the evaporator.
Refrigerant exiting the orifice tube flows into the evaporator core in a low-pressure, liquid state. Ambient air is drawn through the HVAC module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant to boil inside the evaporator core. The boiling refrigerant absorbs heat from the ambient air and draws moisture onto the evaporator. The refrigerant exits the evaporator through the suction line and flows back to the compressor in a vapor state, completing the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.
The conditioned air is distributed through the HVAC module for passenger comfort. The heat and moisture removed from the passenger compartment condenses, and discharges from the HVAC module as water.
