To successfully replace a thermostat, you must understand the functions the various terminals and their wires play, especially the O and B wires, because they affect your unit’s ability to heat and cool your home.
Does My Heat Pump Use O or B Wire?
Your heat pump uses O and B wire. O wire shift the reversing valve from heating to cooling while the B wire does the opposite (Cooling to Heating).
The O and B wires are easy enough to spot because they are ‘Orange’ and ‘Dark Blue,’ respectively. They work in tandem with the reversing valve, a tool that affects the flow of refrigerant.
Does every unit offer O and B wires? Not necessarily.
Some systems have one wire (O/B). Though, the principle of the wire’s operations remains relatively unchanged.
If you have O and B wires and terminals, you can safely conclude that you have a heat pump.
You can confirm this conclusion by checking the thermostat’s settings and searching for an emergency heat setting, which you tend to find in heat pump thermostats. As to whether you should use an O or B wire, it depends on the unit.
There are some factors that many consumers don’t consider.
Your location affects the wire the manufacturer will use. Manufacturers do not expect their products to work indefinitely. They know that HVAC units and heat pumps will fail at some point, and they want that failure to occur on a mode that helps the consumer.
For instance, if you live in a cold region, the manufacturer wants the heat pump to fail on heat mode. If your weather is warm, the manufacturer wants the pump to fail on cool mode.
Imagine a situation where an HVAC in a warm state fails on heat mode. This would be the worst-case scenario. You would be better off if that unit used the B wire in its configuration.
How To Tell If Heat Pump Is O or B?
Check the configuration. The heat pump is ‘O’ if it energizes in cooling and ‘B’ if it energizes on heating.
Thermostats use the B terminal in systems with a reversing valve that turns on with heat mode. The system uses the O terminal if the reversing valve turns on while running cooling mode.
Some people confuse their wiring. As a result, their unit won’t heat when they set it to ‘Heating’ or cool when they set it to ‘Cooling.’
If anything, they may feel cold when the heat pump should warm them or hot when the pump should cool them. You encounter the same problem when connecting the W wire to the wrong terminal. It controls the first heating stage in certain units.
Does O/B Wire Change With Brands?
The brand makes a difference. Most manufacturers use the O wire for reversing the valve. The primary exceptions are Rheem and Ruud. They energize the reversing valve on the heating mode. They use the B wire.
What is the O Terminal on a Heat Pump?
The O terminal allows the heat pump to switch from heating to cooling. O position is an option that allows the reversing valve to ‘default to heating mode.’
The O wire should connect to the O/B terminal. The O Wire can run to the W terminal, but that only applies to conventional systems. You must run the O wire to the O/B terminal if you have a heat pump.
If you cannot determine whether or not you have a heat pump, look for wires in the W2/AUX terminals. Wires in these terminals prove that your system has auxiliary heat, which shows that you have a heat pump.
If you don’t have wires in the E terminals or an orange wire in the O/B terminal, don’t concern yourself with heat pumps and their configurations.
What is the B Terminal on a Heat Pump?
The B position is associated with the reversing valve when it defaults to the cooling mode. The terminal switches the system from cooling to heating. B is the position that changes to the heat relay.
The B wire is typically dark blue. However, you can’t necessarily identify it by its letter or color because it has already noted that blue wires are the common or C wires.
C wires transmit electricity to the thermostat, making sure that it has a reliable power supply at all times.
Admittedly, manufacturers use various colors to identify the C wire. They don’t have to use blue. Thermostats do not have a coloring standard to which manufacturers must adhere. But you are more likely to see a blue or black C wire in a thermostat.
B wire in some thermostats acts as the common C wire. Don’t expect manufacturers to label the common wire with a ‘C’ in every situation. This is why the manual is so important.
If you consult your manual, it will tell you what the various letters and colors mean. If you still have doubts, call a professional. You don’t want to wire the thermostat poorly.
Either it won’t work, or it won’t perform the tasks you expect. For instance, it will cool when you want it to generate heat or keep you warm when you want it to lower the temperature.
An expert can study the wiring to ensure that the valve is energized in the right setting.
What is O/B Terminal?
The O/B terminal allows the heat pump to navigate the heating and cooling functions. You find the O/B terminal on systems with a heat pump. If you have a conventional system, it will use a W terminal.
Does Heat Pump Have C Wire?
C wires matter to modern thermostats because they have many sophisticated features and functions. That includes internet connectivity and LED screens. Without the C wire, you cannot take advantage of all the functions an intelligent thermostat brings to the table.
A common wire gives a thermostat consistent power. You don’t need constant power if you have a traditional thermostat.
Some thermostats have batteries. However, batteries can fail. A common wire is more reliable. Common wires can be blue or black. Some thermostats have them, but the technician decided to leave them unconnected because they did not value the cables.
If you can find the common wire behind your thermostat, you can connect it if you know what you’re doing. Otherwise, call your contractor and find out why they ignored the C wire. They may have a sound reason.