Thermostat Wiring Diagram
The thermostat wiring diagram is the same for all air conditioning systems in a 99%.
Unless any modifications have been made to these systems, the thermostat wiring diagram should have the basic white and red wires going to and from the air conditioner condensing unit. One wire is connected directly to the Y thermostat terminal and the other originates from the air handler and they both terminate in the condensing unit.
The basic colors in the thermostat wiring diagram are red, yellow, white, green, black, orange and blue depending on the unit’s manufacturer.
The red wires within the thermostat wiring diagram stand either for the R terminal, the RC terminal or the RH terminal. The R terminal represent the power supply to the thermostat. This wire usually comes from the transformer which is, on a regular basis, placed in the air handler. This wiring can split between either cooling or heating systems and this where either the RC or RH or both terminals come int he diagram. The RC terminal withstands the power for the cooling system and the RH terminal supplies power to the heating system. These systems can be supplied simultaneously or you can install a switch, to direct power to one or the other, in the same thermostat unit.
The Y terminal is coloured in yellow and this is used for cooling or air conditioning as it is connected to the compressor relay. On more complex air conditioning or cooling systems you have a second stage cooling which is controlled by the Y2 terminal which is also coloured in yellow.
The W terminal enables you control to the heating system and it is wired with a white wire. This wire is usually directly connected to the heating source, regardless if it is gas, oil or electricity based heating unit. Just as in the case of cooling systems, heating systems may enable you the choice for second stage heating, and your thermostat wiring diagram will have the W2 terminal to provide you control over this second stage.
Both the Y and the W terminals may find their way in a thermostat wiring diagram as you are mot required to have several thermostats throughout your house to service each appliance.
The G terminal in the thermostat wiring diagram represents the green wire which controls the indoor blower fan. This may also come equipped with a switch to enable control for an outdoor blower fan.
The energy all these terminals need to properly function is transformed by the C terminal. this terminal isn’t presented in the thermostat wiring diagram as having an universal color, however the most commonly used color is black.
The O or B terminal are used to enable control over the heat pump. Heat pumps usually have a backup system to them and this can be turned on through the E terminal which stands for emergency heating. This terminal has no universal color coding either although it should be easy to spot in the thermostat wiring diagram by elimination.
Another terminal that may appear in your thermostat wiring diagram is the AUX terminal, which is also not universally color coded, this terminal is also designated for heating backup purposes.