Do It Yourself
Inspect Your Thermostat
The thermostat is where you have the most control. It is at the thermostat that you set your desire temperature, therefore if it cant communicate what you want, then the unit cant know what to do.
Even more modern thermostats can be battery operated so make sure to change the batteries at least every 2 years. Thermostats can also range from basic to complicated so its best to be somewhat familiar with your specific thermostat.