Heat performance tuneup times three systems. Changed out customer supplied filters. Inspect blowers, evaporators and ductwork. Checked all safety features how limited rollouts. Tighten the wire connections. Verified all thermostats are operating properly at this time. No carb monoxide or gas leak detected at home. Systems are 12 years old and are operating fine at this time. Although given the age of the systems they are prone to break down at the worst time. Recommendation is to start thinking about new equipment. I