I arrived for a new customer no heat call. I first spoke with the homeowner and found that they have had another company out and the system runs different from before. I inspected the system and found the system to be running normally but the difference is that they now have a T6 thermostat vs the old Mercury bulb thermostat. I cycled the system in emergency heat and in heat pump modes. I also ran it in ac mode. I do that the system is low on R22 and is running at a superheat of 26 and what is recommended is 14 deg. The system is a duel fuel system with a propane furnace and a slab coil. The outdoor system is a heatpump. I explained how the system runs and now that is has a digital thermostat the system will operate different even tho it’s the same system. I recommended to start planing on replacing the system vs repairing the system.