A/C Signal: Description and Operation

Air Conditioning (A/C) Signal (Vehicle with A/C only)
This signal is sent from the A/C amplifier. The A/C amplifier outputs this signal to ECM (PCM) when A/C ON conditions are satisfied on the A/C amplifier side. (The air conditioning does not turn ON in this state.) When ECM (PCM) detects through the A/C signal that A/C ON conditions are satisfied on the A/C amplifier side, it uses the A/C signal as one of the factors to output A/C ON signal and to control IAC valve and fuel injection respectively.

Battery Voltage
The fuel injector is driven by its solenoid coil based upon the ECM (PCM) output signal.

There is some delay called as "Ineffective injection time", which doesn't provide fuel, between ECM (PCM) signal and valve action. As the ineffective injection time depends on the battery, voltage, ECM (PCM) takes voltage information to compensate it in fuel injection time.