Diagnostic call for no heat. Homeowners are saying when they turn the system on in the morning when it is very cold outside that it works fine for a while then starts to blow cool air. I explained to them how a heat pump works since no one had explained it to them before and how the system will usually go into defrost mode when it is very cold outside. Adjusted settings on thermostat due to system not having heat strips. Per Christopher’s authorization I informed homeowner that if they still feel it’s a problem now that they know how it works and if they feel the house is getting too cold during the defrost cycle To call back in for us to come back and install heat strips to make sure they are comfortable and happy. System is operational and heating at this time