The $4,200 Lesson I Learned About Skipping Tune-Ups Three years ago, I made what seemed like a smart financial decision. Why pay someone $150 every year to "check" my air conditioner when it was running fine? The unit cooled the house. No weird noises. No problems. That logic cost me $4,200 one July night when the system died during a heat wave. But here's what really stung — the...