Headlights dim when using AC — normal or problem?

A brief dim when the AC compressor kicks in is normal — the compressor clutch engages and puts a sudden load on the engine/alternator. But if they STAY dim or it happens repeatedly while driving, your alternator is getting weak. These Malibus use a clutch-type compressor that cycles on and off, so you might notice it at every cycle. Get the alternator output tested — should hold 14V+ even with AC on and headlights on.

Also check your serpentine belt. A glazed or slightly loose belt will slip when the AC compressor engages, momentarily reducing alternator output. Belt should have no cracks and proper tension. The tensioner on these Malibus wears out around 80-100k miles.