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. After 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.

The PCM will engage the A/C clutch any time the engine speed is below 5000 RPM and the A/C is requested unless any of the following conditions exist:
^ Throttle angle is 100 percent
^ The A/C refrigerant pressure sensor is less than 186 kPa (27 Psi)
^ The A/C refrigerant pressure sensor is more than 2979 kPa (432 Psi)
^ Engine Coolant Temperature (ECT) is more than 121°C (250°F)

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 selling 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.