Connect thermostat terminals to the indoor air handler and outdoor unit using the standard low-voltage control cable layout. Most residential climate systems built by this manufacturer rely on a 24-volt control circuit with several labeled terminals. The R terminal supplies control voltage, C provides the common return path, Y activates the compressor, G controls the indoor fan, and O or B operates the reversing valve.
Use a multi-conductor thermostat cable with at least five insulated leads. In many installations, red connects to R, blue or black connects to C, yellow activates the compressor contactor, green controls the blower motor relay, and orange manages the reversing valve used during cooling mode. Confirm terminal labeling on both the air handler control board and the outdoor condensing unit before attaching conductors.
Route the control cable from the thermostat location to the indoor air handler cabinet, then continue toward the outdoor condensing unit through a protective conduit or sealed wall passage. Keep the control cable separated from high-voltage supply lines by at least several centimeters to reduce electrical interference.
Verify voltage and signal operation after installation. Measure approximately 24 volts AC between R and C at the control board. Activating cooling at the thermostat should energize the compressor contactor through the Y conductor, while fan mode should trigger the indoor blower relay through the G conductor.
Carrier Heat Pump Wiring Diagram with Thermostat Terminals and Control Board Layout
Connect the thermostat conductors to the indoor air handler control board using the standard 24-volt terminal layout. The R terminal supplies low-voltage power from the transformer, while C acts as the return path. Y activates the outdoor compressor contactor, G starts the indoor blower relay, and O or B energizes the reversing valve used to change between cooling and heating operation.
Use a multi-core thermostat cable routed from the wall controller to the air handler cabinet and then to the outdoor condensing unit. Typical conductor colors help keep connections consistent. Red usually links to R, blue or black connects to C, yellow connects to Y for compressor activation, green operates the fan circuit, and orange commonly controls the reversing valve. Match terminal markings on the air handler board and outdoor unit terminals before tightening screw connectors.
Control Board Terminal Layout
The indoor control board distributes 24-volt signals to different relays and contactors. When the thermostat calls for cooling, voltage travels from R through the Y conductor toward the outdoor unit contactor coil. This closes the contactor and allows high-voltage power to reach the compressor and outdoor fan motor. A call for fan operation routes voltage from R through the G terminal to the indoor blower relay.
Signal Verification
Measure voltage between R and C at the control board to confirm transformer output. A stable reading near 24 volts AC confirms the control circuit is active. Activating cooling mode should send the same voltage through the Y conductor toward the outdoor unit, while fan mode should energize the G conductor and start the indoor blower motor.
Secure control cables with insulated clips and keep them separated from high-voltage supply lines feeding the compressor or blower motor. Maintaining physical separation reduces electrical interference and prevents insulation damage caused by vibration or contact with sharp metal edges inside the equipment cabinet.
Carrier Heat Pump Wiring Diagram for Thermostat Terminal Connections R C Y O B and G
Connect thermostat conductors to the indoor air handler control board according to the labeled terminals before restoring power. The low-voltage control circuit usually operates at about 24 volts AC supplied by the system transformer. Each terminal on the thermostat base sends a signal to a specific component inside the air handler or outdoor condensing unit.
Typical terminal functions follow a consistent pattern across many residential climate systems.
- R – 24 volt supply from the transformer
- C – common return path completing the control circuit
- Y – signal sent to the outdoor compressor contactor
- G – indoor blower relay activation
- O – reversing valve energized during cooling mode
- B – reversing valve energized during heating mode on some systems
Attach each conductor securely under the terminal screw and confirm color consistency between the thermostat base and the indoor control board. After installation, restore power and test operation: cooling demand should energize the compressor through the Y conductor, fan mode should activate the blower through G, and the reversing valve should shift position through the O or B conductor depending on system configuration.