These are some steps you can take to possibly avoid a service visit. They are in no particular order.
- Check if the thermostat is on. If it takes batteries, try changing them.
- Check if there are any breakers off. If there are try resetting them. (Only try this once)
- Have you replaced the filter lately? Check the filter. If it is very dirty, replace the filter, then turn the AC/Furnace off (wait 1 minute) and then back on again.
- If your AC/Furnace is in a basement, there may be a "Kill Switch" at the top of the basement stairs. They sometimes have a red cover plate on them, but they look just like a light switch. Make sure it is on.
- If you have a newer gas furnace, check the white PVC vent pipes outside. They could be blocked with snow or other debris.