5 Wire Honeywell Thermostat Wiring Diagram

Wiring a Honeywell Round Mercury Thermostat may seem daunting at first, but with a little guidance and the right tools, it can be a straightforward process.. Double-checking the connections and referring to the wiring diagram can help identify and rectify any wiring mistakes. 2. Loose or Damaged Wires.. The wiring diagram of a mercury thermostat typically consists of several labeled terminals or wires, each serving a specific function. These terminals include the "R" terminal for power supply, the "W" terminal for the heating system, the "Y" terminal for the cooling system, and the "G" terminal for the fan..

Here is a breakdown of the typical wiring connections for an old Honeywell mercury thermostat: Red wire: This wire is usually connected to the R terminal and carries the 24-volt power supply from the HVAC system.. It is important to refer to the thermostat's wiring diagram and ensure that the wires are connected to the correct terminals.. Page 6: Wire The Thermostat CT87A,B,J ROUND® THERMOSTAT Wire the thermostat 1. Use the wiring cross-reference table below to match each old thermostat wire with its corresponding terminal on the CT87 wallplate or subbase. See Figs. 8-13 for wiring diagrams. Wiring cross-reference Connect to Connect to Connect to Wire label CT87A.