York’s HYBRID system using our Affinity Modulating furnace and Affinity Heat Pump with the York Guard VI control, have a unique distinction of being able to run the heat pump simultaneously with furnace by simply adding a bonnet sensor between the top of the furnace and the inlet of the evaporator coil.
When the bonnet sensor is not used, the heat pump will turn off within 30 seconds of the furnace starting. This is done so the heat off the furnace does not cause the high pressure switch to trip due to the high temperature onto the coil. This can cause cold air to blow until the furnace comes up to temperature. This is standard operation on most manufacturer’s hybrid system heat pump / gas furnaces.
When the bonnet sensor is added to the York Hybrid System, it allows the furnace and heat pump to operate simultaneously eliminating the “cold blow” during transition from heat pump to just gas furnace. The heat pump will remain energized as long as the bonnet sensor senses temperature below 90 degree F. This allows the furnace to come up to temperature before the heat pump shuts off eliminating the cold blow. And, since the Modulating Furnace runs at 35% capacity for the first 6 minutes and then slowly ramps up to 100% capacity over the next 16 minutes, the transition from heat pump to gas furnaces keeps the air warm during the whole process.
The bonnet sensor also helps during defrost to keep the house warm during defrost operation when the indoor coil is now cooling coil. It is a nice feature to add to a Hybrid System. For more information on the sequence of operation with or without the bonnet sensor, please contact your local York distributor.
There is one thing that needs to be kept in mind with the York Hybrid system –with a standard heat pump thermostat, the bonnet sensor is wired into the York Guard VI control in the outdoor unit at terminal BSG & BS. However, when a TTSCC York Communicating Control is added to the system, the sensor MUST be attached to the Modulating Furnace control board and not to the outdoor unit. It is the same sensor but, if it is run to the outdoor unit, a fault will show up on the Communicating Control saying it is an incompatible sensor and the self discovering configuration will be incorrect.
In order to attach the sensor to the Modulating Furnace board, there is an adapter that needs to be ordered when you order the sensor.
I have attached a “tips letter” at the end of this posting that you can print out and save for future reference that also includes the sensor and adapter part numbers. Hopefully this will help you eliminate a possible problem before it occurs.