When installing a programmable thermostat for a heating and cooling system with a single control circuit transformer, which jumper must remain connected?

In a heating and cooling system that utilizes a single control circuit transformer, the jumper between the RC (cooling) and RH (heating) terminals must remain connected. This connection is essential because it allows a continuous power supply to the thermostat regardless of whether the system is in heating or cooling mode. When a single transformer is used, it typically serves both functions, and maintaining this jumper ensures that the thermostat can effectively operate in both scenarios without interruption.

By having the jumper between the RC and RH terminals in place, you facilitate the proper functioning of the thermostat and allow it to switch between heating and cooling modes seamlessly. Without this jumper, the thermostat may not receive the necessary power, leading to malfunctions or an inability to control the system efficiently. Thus, ensuring that this jumper remains connected is critical for the reliability and functionality of the thermostat in your heating and cooling system.