Air conditioner: repair, replace, or maintain?
Air conditioner is weak: last year it took upwards of 3 hours to get the house to 21 degrees, and even sitting directly near a vent did little. The house is 1500-2000 square feet with a finished basement, semi duplex. Normally I would open windows and use ceiling fans (installed on all floors except basement), but with a new baby on the way we're leaning towards making more use of air conditioning this year. I've never had a house with air conditioning before (last residence was a condo so I left it to the condo corporation to manage that, and my parents' houses never had air conditioning), so I'm not sure what is "normal" for maintaining these units.
What would be the recommended course of action? Can you overhaul an air conditioner like you can with a car engine to bring it back to spec? Or would it be better just to replace? Some sites say 10-15 years is average lifespan, which makes me think this one is about ready to go.