Thank you for your reply.
Under normal conditions, it is the battery voltage.
When the fan speed is 1 to 4, the voltage is 1.2 to 2 volts.
According to the Mazda manual, the judgment that the AC works is less than 3 volts.
So this voltage seems to be correct.
The problem that the AC request was not correctly recognized by the plug-in ECU also occurred to a friend other than me.