Buying the correct thermostat for an air conditioning unit depends on knowing what type of HVAC unit you have.
Thankfully, manufacturers set up most thermostats to accommodate almost any system, but it still helps to know what type of HVAC system you have.
Types of Air Conditioning Systems
If your unit can heat and cool without a furnace, then you have a heat pump.
Air Conditioning only Units
Standard air conditioning units only cool the home and need a furnace to heat during the winter.
Wiring a thermostat is not difficult with some basic information.
First off, always document the old thermostat wiring by taking good pictures or writing the color codes and what terminals they go to.
Keep in mind that while there is a color code that is supposed to be used, it is not always followed.
By examining the old wiring going to the old thermostat, this can be taken into account.
Often simply copying the old wires and terminals into a new thermostat can be done.
How a Thermostat Works
Thermostats control large components in an A/C unit, such as the compressors and fans. These components use high voltage, while a thermostat uses only 24 Volts to control them.
It does this through what are called relays that are engaged when 24 volts are applied to them.
A relay will have high voltage going in on one side and a component wired in on the other side.
When 24 volts is applied to a relay, a coil creates a magnetic effect pulling down a metal lever that completes the circuit for the high voltage to go through.
A thermostat is nothing more than an automatic switch that controls turning on or off the correct components depending on the temperature.
Common Wiring Color Codes and Terminals.
C———This is the common wire from one side of the transformer, which is 24 Volts AC.
R———The other side of the transformer also 24 Volts AC. This is the hot side of the transformer.
G———Turns the fan on.
W——–Call to turn on the heat.
Y———Call for cooling.
Depending on your system, many of the above terminals may not be used.
The main thing to look at is the 24 volts coming in on “R” and “C” terminals.
The “Y” terminal is a call to turn on the air conditioning, which will apply 24 volts from “R” at the “Y” terminal when cooling is needed.
Types of Thermostats
Standard basic thermostats work well and are commonly used since they are cheap.
Today more than ever before is a wide range of thermostats, from WiFi thermostats that can control a homes temperature, to touch screen thermostats that have weather forecast.
So let’s take a look at thermostats to see what types are available.