Theory Of Operation

WARNING: This page is about a different car, the 2015 Fiat 500. However, it is still accessible from the selected car via links, so may be relevant.

The Powertrain Control Module (PCM) receives a signal requesting the A/C Compressor to be turned on from the HVAC. When the PCM receives this request it grounds the control side of the relay. The Powertrain Control Module (PCM) receives feedback from the A/C Pressure Transducer to monitor the pressure in the high side of the A/C refrigerant system. The A/C Pressure Transducer connects to a fitting on the A/C discharge line and its internal resistance changes in response to the pressure in the system. The PCM provides a 5-Volt reference signal and a sensor ground to the A/C Pressure Transducer, then monitors the output voltage of the transducer on the sensor signal circuit to determine refrigerant pressure. The PCM is programmed to respond to this and other sensor inputs and control the operation of the A/C Clutch and the Radiator Cooling Fan to help optimize A/C system performance and to protect the A/C system components from damage. The PCM will request disengagement of the A/C Clutch when high side pressure rises above the calibrated maximum limit and re-engage the clutch when high side pressure drops back below the limit. The PCM will also disengage the A/C Clutch if the high side pressure drops below the calibrated minimum limit and will re-engage the clutch when the high side pressure rises back above the limit. When the refrigerant pressure rises above a calibrated pressure specific to the PCM, the PCM will actuate the cooling fan.