Diagnose and fix Toyota no AC
Late model Toyota vehicles use a refrigerant flow sensor in addition to the normal low and high pressure switches. The flow sensor is located in the AC compressor. The ECM uses information from the flow sensor to vary engine idle speed to prevent stalling. If the sensor is bad, the AC amplifier won’t send the proper digital signal to the ECM and the ECM won’t engage the AC compressor clutch. You wind up with a Toyota no AC condition.
Toyota no AC symptoms
The AC in your car blows warm. You check the AC compressor and discover the compressor won’t engage when you turn on the AC. Start diagnosis with scan tool. You’ll need a high end scan tool to see a body “B” code. A bad flow sensor will usually show as B1479 open or short in AC flow sensor circuit trouble code.
How the AC flow sensor works
The Toyota AC flow sensor in the compressor receives a 5-volt reference voltage from the AC amplifier located to the right of the accelerator pedal. It varies the output voltage back to the AC amplifier based on refrigerant flow.
Use your scan tool to see if the ECM is receiving an AC ON request from the AC amplifier. If you don’t see that request, perform these tests.
Test the Toyota AC flow sensor
1. Check for 5-volt reference signal on the white wire
2. Check for flow sensor voltage on the red wire.
With the AC OFF and blower switch OFF the voltage on the red wire should be 3.8 to 4.2-volts.
With the AC ON and Blower on HIGH, the voltage on the red wire should be 0.7 to 3.8-volts.
If voltage is less than 0.7 or higher than 4.2, sensor is bad
If no signal on red wire but you see 5-volt reference on white wire, sensor is bad
Replace the sensor
To replace the AC flow sensor you must first evacuate the entire system and reclaim the refrigerant and measure the oil removed. Then replace the sensor. Add the same amount of oil. Evacuate again. Then add a full refrigerant charge.
©, 2019 Rick Muscoplat
Posted on by Rick Muscoplat