Pinpoint Test L : The Air Conditioning (A/C) Is Inoperative: Notes

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

Diagnostic Overview

Diagnostics in this article assume a certain skill level and knowledge of Ford-specific diagnostic practices. Refer to Diagnostic Methods in Service Information for information about these practices.

Refer to Automatic Climate Control System , for schematic and connector information.

Normal Operation and Fault Conditions

When the A/C is requested, the FCIM sends the button press message over the I-CAN to the IPC. The IPC sends the button press message to the BCM over the HS-CAN. The BCM sends the button press message to the HVAC module over the MS-CAN. The HVAC module sends an A/C request message through the MS-CAN to the BCM and the BCM sends the A/C request through the HS-CAN to the PCM.

Voltage is provided to the A/C clutch relay coil and switch contacts. When A/C is requested and A/C line pressures allow, a ground is provided to the A/C clutch relay coil from the PCM, energizing the A/C clutch relay. When the PCM energizes the relay, voltage is supplied to the A/C compressor clutch field coil from the relay. Ground is supplied for the A/C compressor clutch field coil.

An accurate evaporator temperature is critical for compressor engagement. The PCM uses the temperature measurement to turn the A/C compressor off before the evaporator temperatures are cold enough to freeze the condensation on the evaporator core.

When an A/C request is received by the PCM, the A/C compressor clutch only engages through the A/C clutch relay if all of the following conditions are met:

The PCM does not detect excessively high or low refrigerant pressure from the A/C pressure transducer.
The PCM does not detect excessively high engine coolant temperature.
The PCM does not detect an ambient air temperature below 1 °C (33.8 °F).
The PCM has not detected a WOT condition.
The HVACcontrol module does not detect an evaporator temperature below 1 °C (33.8 °F).

Possible Sources

Fuse
Wiring, terminals or connectors
A/C system discharged or low refrigerant charge
Network concerns
Evaporator temperature sensor
A/C pressure transducer
A/C compressor clutch field coil
A/C compressor clutch air gap
A/C clutch relay
FCIM
HVAC control module