I have a 2007 Mitsubishi Eclipse that's losing voltage in the cab when the AC is turned on. There's no battery guage, but I do have a phone charger that also reads the current voltage when the car is on. I took it to a mechanic thinking it was the alternator, but nope! Everything in the engine compartment was fine. Alternator was working fine, nothing wrong with the battery.
Could this be a BCM issue or a massive electrical leak in the AC system? This is confusing the veteran mechanics in my area.
losing voltage in the cab when the AC is turned on
I'd be looking at the AC system then. Compressor, clutch, accessory belt, etc.
@imperator AC system looks fine. The issue just got worse as well; it's no longer keeping a steady voltage and it's now affecting the engine.
Just got a new alternator. The erratic voltage is no longer triggered by the AC getting turned on and has dropped down to 9 volts before jumping to 12, so we're thinking that the voltage regulator is dying (and I've double checked: the regulator is built into the alternator, not the ECM, thankfully). Hopefully this'll fix the issue.