Control System Logic

WARNING: This page is about a different car, the 2015 Lincoln MKT. However, it is still accessible from the selected car via links, so may be relevant.

The controls for the climate control system are in 1 or more locations depending on vehicle option content:

FCIM
FDIM (part of APIM)

When the FDIM touchscreen or voice commands are used, the APIM sends a function request message over the I-CAN to the IPC. The IPC sends the information to the BCM over the HS-CAN.

When the FCIM receives the climate control selections from pressing the buttons on its own controls (interface), the APIM or the IPC (remote start). The IPC sends the information to the BCM over the HS-CAN. The BCM sends the requests to the HVAC control module over the MS-CAN.

A/C Request

When the A/C is requested, the HVAC control module sends the message over the MS-CAN to the BCM. The BCM sends the A/C request to the PCM through the HS-CAN.

When an A/C request is received by the PCM, the PCM engages the A/C clutch relay when all of the following conditions exist:

the refrigerant pressure is not excessively high or low.
the engine coolant temperature is not excessively high.
the ambient air temperature is above approximately 0 °C (32 °F).
a Wide Open Throttle (WOT) condition is not present.
the evaporator temperature is above approximately 1 °C (33.8 °F).
the PCM does not detect temperatures from the Mass Airflow/Intake Air Temperature sensor that does not correlate with other temperature sensor readings at ignition ON. (Most Mass Airflow (MAF) sensors have an integrated Intake Air Temperature (IAT) sensor).

The PCM monitors multiple temperature sensors correlation (AAT, CHT, ECT IAT, MAF, MAP (as equipped)). The PCM runs this logic after an engine off and a calibrated soak period, typically 6 to 8 hours. This soak period allows the Ambient Air Temperature (AAT) sensor and the other temperature sensors to stabilize and not differ by greater than a calibrated value, typically 18 °C (32.4 °F). If a sensor input is found to be reporting a temperature imbalance the PCM does not allow the A/C clutch to engage. For more information on PCM sensors, Refer to Engine Controls - Introduction (Except Diesel & Hybrid) .

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 does not allow the A/C clutch to engage.