Controls and Compressor Cycling

WARNING: This page is about a different car, the 2013 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.

The HVAC system uses inputs from the FCIM , FDIM and voice commands to provide the interface for the vehicle occupants to control the climate control system. When selections are made, the FCIM communicates the selections to the HVAC module which adjusts the climate control system components to achieve the desired state. When the climate control system is operating in AUTO mode, the required climate control system settings are determined by the HVAC module. The HVAC module then adjusts the climate control system components to the desired state.

The HVAC module utilizes an FET protective circuit strategy for its actuator outputs. Output load (current level) is monitored for excessive current (typically short circuits) and is shut down (turns off the voltage or ground provided by the module) when a fault event is detected. For additional information on HVAC module FET protection, REFER to CLIMATE CONTROL - DATC , HEATING VENTILATION AIR CONDITIONING (HVAC) MODULE - HVAC .

The PCM monitors the discharge pressure measured by the A/C pressure transducer. The PCM interrupts A/C compressor operation in the event the A/C pressure transducer indicates high system discharge pressures. It is also used to sense low charge conditions. If the pressure is below a predetermined value for a given ambient temperature, the PCM will not allow the A/C clutch to engage.

The evaporator temperature sensor is an input to the HVAC module. The HVAC module maintains evaporator core temperature and prevents icing of the evaporator core by switching the A/C request signal off before the evaporator temperatures are cold enough to freeze the condensation and by switching the A/C request signal on when the evaporator temperature rises above acceptable levels.

The HVAC module adjusts the air inlet door depending on the humidity measured by the in-vehicle temperature and humidity sensor. If the vehicle cabin becomes too humid and recirculated air is selected, the HVAC module adjusts the air inlet door to allow more fresh air. When the humidity level drops, it may adjust back to partial recirculated air. The HVAC module also adjusts the system based on in-vehicle temperature.

The sunload sensor supplies information to the HVAC module indicating the intensity of the sun on the vehicle and the HVAC module will make system adjustments based on the intensity.

When battery voltage is applied to the A/C compressor clutch field coil, the clutch disc and hub assembly is drawn toward the A/C clutch pulley. The magnetic force locks the clutch plate and hub assembly and the A/C clutch pulley together as one unit, causing the compressor shaft to rotate. When battery voltage is removed from the A/C compressor clutch field coil, springs in the clutch plate and hub assembly move the clutch plate away from the A/C clutch pulley.

For more information on compressor operation, REFER to CLIMATE CONTROL - DATC , EXTERNALLY CONTROLLED VARIABLE DISPLACEMENT COMPRESSOR (2.0L/3.5L GTDI) or REFER to CLIMATE CONTROL - DATC , INTERNALLY CONTROLLED VARIABLE DISPLACEMENT COMPRESSOR (3.5L AND 3.7L TWIN INDEPENDENT VARIABLE CAM TIMING (TI-VCT) ).