We are in Florida and the weather has become very cold, in the 30's at night. Last night the house heater was set at 70 degrees, blowing hot air and we were comfortable. This morning we awoke with an interior temperature of 60 degrees, the heater was blowing cold air. What has happened I can not afford a tech, how can I diagnosis myself?

It could be many different things. It is really hard to tell since I have no brand or EXACT model number of the inside and outside units.