Vehicle: 2012 Ford Focus, L4-2.0L, Automatic Transmission/Transaxle

Mileage: 89,306 miles

Problem: The vehicle was brought to the shop because the A/C stopped working.

Case Details: The A/C system’s high and low pressure readings were a little low, so the technician recovered the freon, then recharged the A/C system to factory specifications. Unfortunately, the compressor still wouldn’t activate. He connected a scan tool and checked for diagnostic trouble codes (DTCs), but found none. All scan tool PID data seemed to be normal, except for the intake air temperature (IAT) sensor, which was reading 10°F, though the ambient temperature was about 72°F.

When he read the A/C system description and operation in ALLDATA, he found that the IAT can affect A/C operation, but he thought it was odd that there were no DTCs.

NOTE: Because the PCM was getting a low temperature input signal from the IAT sensor, it inhibited A/C operation without generating any DTCs.

Confirmed Repair: The technician replaced the MAF sensor, since IAT sensor is integrated into the MAF sensor. All PID information read back to normal, and the A/C system worked perfectly. Fixed!