York Hybrid System with Bonnet Sensor

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.



About yorkcentraltechtalk

I have been in the HVAC industry most of my life. I worked 25 years for contractors on anything from residential to large commercial boilers and power burners. For the past 23+ years I had been employed by York International UPG Division ( a division of Johnson Controls) as a Technical support/Service Manager but I am now retired. One of my goals has always been to "educate" dealers and contractors. The reason for starting this blog was to share some knowledge, thoughts, ideas, etc with anyone who takes the time to read it. The contents of this blog are my own opinions, thoughts, experiences and should not be construed as those of Johnson Controls York UPG in any way. I hope you find this a help. I always welcome comments and suggestions for postings and will do my best to address any thoughts, questions, or topics you may want to hear about. Thanks for taking the time to read my postings! Mike Bishop
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2 Responses to York Hybrid System with Bonnet Sensor

  1. Dean says:

    My question isn’t about bonnet sensors but about York hybrid systems defrost operation.
    Although our company mainly install heat pumps with air handlers and electric back up, we do have a fair number of hybrids. a co worker and myself both have York hybrid systems basically identical. His YP9C080 with YZH036 while mine in YP9C060 with a YZH024. Both obviously with YorkGuard VI defrost boards and both system operated with communicating thermostats. These system are behaving the same way. I have been paying close attention to mine. The defrost operation is being initiated in my opinion to often and unnecessarily. Example. My system will be off all night and then as schedule calls for increased heat when I wake up at 6am. System will operate for anywhere from 2-5 minutes then defrost. This happens every morning. I know and have checked no frost on coil and outdoor temp above freezing usually anywhere from about 34-46F here on the west coast of Canada. This seems to happen anytime the system has been off for a period of time with no call. It also defrosts a lot throughout the evening as it works to reach set point. Never any error codes. Now do these defrost boards work on the demand defrost? Difference between coil and outdoor ambient temps? And no defrost above 50F? As I’m off today and was outside system defrosted once again after less than 10 minutes of operation with outdoor temp of 48F and no hint of frost in sight on the coil. Filter new. I have good airflow and static is under .50 IWC as does co workers system. We installed and do it right! All this unnecessary defrost is certainly killed efficiency and component life span.
    My question is have you or anyone experienced this as well? And what troubleshooting or solution is there? Coil sensor? But both these systems acting same way and both about 2 years old.
    Thanks !

    • The demand defrost control boards installed on the AFFINITY heat pump units are manufactured with a six position defrost curve jumper. The jumper
      position is preset at the factory depending on the specific size of the equipment but is field adjustable. For actual curves showing the inhibit, allow etc, you should contact your local distributor. they can provide you with any information on the demand defrost.

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