Question: 24-Volt Thermostat Wiring For Single-Stage Heat Pump Systems
I was recently asked if I could help with the installation wiring of a single-stage heat pump system. The thermostat connections are often confusing if you don't know what they each do and how the heat pump system is connected. I'll do my best to explain the connections and what they are used for.
Properly connecting the right colored wires to the appropriate terminal connection is crucial.
Each wire has its specific use and specially colored wire is identifiable to the technicians that connect and maintain these units. The wire color standard makes it easy for whoever comes to work on the device, an easier path to tracing circuit paths and troubleshooting possible problems.
Always remember to properly strip the insulation completely off the wires to ensure the connection point is touching 100% of the copper wire. This will ensure a quality connection point and allow the device to function properly and effectively. Here are the normal connections on the thermostat that you likely have and the connection points.
The G terminal controls the fan relay and is responsible for turning the blower fan on and off automatically or manually via the thermostat.
The RC terminal is the 24-volt cooling power supply.
The RH terminal is the 24-volt heating power supply.
- Note: The RC and RH terminals are jumpered together in a four-wire heat/cool system and a single-stage heat pump system, but not in a five-wire heat/cool system.
The Y/O terminal is used to control the cooling contractor. When the thermostat calls for cooling, power is fed to pull in the cooling contactor and the fan relay. This powers up the condenser and the blower fan, cooling your home.
The W/B terminal controls the heat relay or valve. When the thermostat calls for heat, power is fed to pull in the heat relay or valve and the fan relay. This powers up the furnace and the blower fan or the boiler, heating your home.
The Y1 terminal is used for the compressor contact in a single-stage heat pump installation.
First of all, RC and RH are jumpered together providing the power. This combo connection is then wired to the heat pump's 24 volt supply. The G terminal is the fan relay connection. This turns the fan on when heating or cooling is called for. The Y/O, used for the cooling mode, is connected to the reversing valve. Also connected to the reversing valve is the W/B, used for the heating mode, keeping in mind to connect to the appropriate terminal on the heat pump connection terminal. The Y1 connection is the cooling compressor connection that pulls in the compressor when the thermostat calls for cooling.
As you can see from the above information, the heat pump system connections on a programmable thermostat are a little different than a 4- or 5-wire heat/cool system wold be wired. The actual wiring isn't that difficult if you have the information to follow and a little wiring experience. Go ahead! Give it a try. If you're not sure the connections are right, you can always call a professional to examine the connection points before firing it up.