Call was originally scheduled for Friday the 17th. But due to the weather being too cold to check the charge on this heat pump I decided to wait until today when it was 70°. When I arrived I informed David that I was going to put it in the test mode outside. After system ran for about 10 minutes it gave me a charged indication. I advised David that newer systems are designed to run down to a minimum of 25° on the thermostat auxiliary lockout. 35° is what David had previously on his previous thermostat. System is a 13 year old dual fuel heat pump. When the temperature is mild the heat pump runs just fine. I advised David when it gets extremely cold to switch it directly to emergency heat so the heat pump will not fail prematurely. I also advised David that his windows are a high concern for his HVAC system too. They are single pane and weatherstripping is weathered. We can give a no cost estimate at any time.