Here are some simple things homeowners can check before calling: 1. Check your thermostat—Do you have it set for heating or cooling and is the choice appropriate for the season or is it inadvertently in the "off" position? 2. Check the air filter. If it’s very dirty – if it hasn’t been changed in months and it’s clogged with dirt – your system’s working hard to get ANY air through. Replace the filter and see if the system then operates properly. 3. Check that nothing is