Vehicle: 2014 Ford Fusion, FWD, L4-1.5L Turbo
Problem: This vehicle was brought to the shop because the A/C was blowing hot air from all vents.
Details: The system was evacuated and recharged just to confirm the refrigerant level was at specification (20oz). The technician attempted to command the A/C compressor “ON” with a scan tool, but it would not engage. When he scanned for diagnostic trouble codes (DTCs), he found DTC P0073 – Ambient Air Temperature (AAT) sensor circuit high.
He followed the Ford diagnostic Pinpoint Test “FA” in ALLDATA and determined that the AAT sensor was faulty (reporting -40°F). He replaced the AAT sensor and cleared the DTC.
At that point, there were no codes, but the A/C compressor still would not engage. If power was applied directly to the compressor, the system would engage and operate as designed. A call was then made to ALLDATA Tech-Assist.
The Tech-Assist consultant advised using the scan tool to review A/C-related temperature and pressure sensors to verify that they all reported accurately and rationally to each other. He further suggested checking to see if the PCM was denying any A/C requests.
The tech inspected the A/C temperature and pressure sensors as advised. He found that the A/C pressure transducer reported only 4 psi in all conditions. Using the wiring diagrams as a guide (see image), he verified that the circuit integrity was good and the PCM was not at fault.
Confirmed Repair: The tech replaced the A/C pressure transducer and cleared the DTC. After the repairs, the A/C operated as designed and the DTC did not return. Fixed!