AC compressor clutch won’t engage on Toyota

Fix B1479 Flow sensor and AC compressor clutch won’t engage

If the AC compressor clutch won’t engage on your late model Toyota and you find a B1479 Flow Control Circuit trouble code stored, the problem is usually a bad flow control sensor. Toyota uses the AC flow control sensor to detect the amount of refrigerant flow through the compressor. Based on the reading, the ECM can adjust idle speeds and engine load parameters to save gas.

The AC flow sensor converts flow rate to a voltage that’s sent to the AC amplifier which communicates digitally with the ECM.

A B1479 Flow Control Circuit code indicates either a short or open in the flow control sensor circuit. To eliminate the possibility of an open to the sensor, disconnect the electrical connector and check for 5 volts. The flow control sensor receives 5V DC from the AC amplifier. It then monitors the change in that voltage to determine flow rate. If you detect 5V from the AC amplifier, turn on the AC and check for return voltage. It must be above 0.3V and less than 4.7V and should vary. If it reads below 0.3V or higher than 4.7V (gor more than 5-secs), replace the sensor.

How to fix a B1479 and AC compressor clutch won’t engage

Unfortunately, Toyota doesn’t seem to sell just the sensor and recommends replacing the entire compressor. However, some sources in China (Alibaba) do sell the sensor. Keep in mind that you’ll have to discharge the refrigerant to replace the sensor. Then you’ll have to pull a vacuum and recharge.

©, 2016 Rick Muscoplat

Save