Last night, while camping in our hi-lo, we noticed that when we turn on the AC unit, the 12 volt lights get brighter. Anyone know why?

The only reason that could happen is that the battery voltage increased. My guess is, the converter somehow increased the battery charging voltage when it passed the 120V AC power to your Air Conditioner. Possibly, the battery charging state was in "float" (a maintenance state) and transitioned to a higher "bulk" or "absorption" mode. I don't know why it should do this however.

- Jack

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Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH, Progressive Dynamics Converter, Fan-Tastic Fan, LiFePO4 battery 12V DC Electrical System
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew

Is this the original converter? Talk to one of the techs at Best converter. Have your converter model available. Jack is usually spot on with his advice. I have experience when the furnice kicks in that our lights would dim. This meant that we had to replace the original converter.