Thermostat Wiring Diagram with Air Conditioner, Fan, Heat Pump

Hey, today we are going to see Thermostat Wiring Diagram. Here you will find the basic wiring diagram of thermostat with Air Conditioner, Heat Pump, and Blower Fan. The thermostat is very useful device for HVAC installation in our house. Electronic Engineering makes our daily life more and more relaxable. Temperature control using the Thermostat is one of the best examples.

The thermostat is basically a temperature control switch. It goes ON and OFF according to the temperature condition. Basically, it has a bimetallic strip and gas-filled bellows inside it. Anyway, let's go to our main topic which is a simple thermostat connection.

Wiring Diagram of Thermostat

Here we have taken a Four-Wire Thermostat. It is the simplest thermostat that can be installed at home. 
As you see in the below diagram the thermostat has four terminals and they are different colors such as Red, White, Yellow, and Green.

First of all, let's find all terminals,
  • Red - For Power input.
  • White - For Heating Enable
  • Yellow - For Cooling Enable
  • Green - Control the Fan

Thermostat Wiring Diagram, wiring diagram of thermostat

Remember that the above diagram is the control diagram. That is why the whole circuit is connected to 24V AC. The main AC supply(230V) is to be given separately to the  A/C, Heat Pump, and Fan.

1. Here a 24V Transformer is used to provide the 24V AC to the whole circuit including Relay, Contactor, etc.

2. The terminal 'R' of the thermostat is connected to the transformer power supply.

3. The "W' terminal is connected to the heat pump for heating purposes.

4. The 'Y' terminal is going to the Air conditioner. Actually, this terminal is not directly connected to the air conditioner. It is connected to the Contactor which turns On and OFF the A/C according to the signal that comes from the Thermostat.

5.  The 'G' terminal is connected to the blower fan inside the air handler. This fan is used to circulate the hot air and cold air.

6. Here the blue wire is the common wire for all loads i.e. Blower Fan, Heat pump, A/C, etc.

According to the temperature condition inside the room, the thermostat creates signals and feeds to the heat pump, A/C, fan, etc. Thus the thermostat maintains a desired temperature inside the room.

Color Code and Terminal for Heat Pump Thermostat Wiring

Now, we are going to discuss the wiring guide for an electronic thermostat that is used with a heat pump. There are various types of electronic thermostats are available in the market. Before connecting any thermostat it is suggested to check the manual. Here, the thermostat shown in the below figure is supplied by a 24V AC power supply.

Heat Pump Thermostat Wiring Diagram

The 24V AC supply is to be connected to the Red and Black terminals. The red terminal is marked as R and the black terminal is marked as C. The signal for the cooling air conditioner is supplied from the Yellow(Y) terminal. When the temperature is high it will send a signal to the air conditioner to cool the room. The green terminal is connected to the indoor fan that circulates the air inside the room. The O and B terminal is used when there are reversing valves available in the system. The reversing valve for cooling is to be connected to the O terminal whereas the reversing valve for heating is to be connected to the B terminal.

The 2nd stage cooling system is used to make more cool the room. Y2 terminal is used for this purpose. The color of this terminal is varied for different models, and systems.

The 2nd stage heating system is used to make more heat in the room. W2 is used for this purpose. The color of this terminal also varies for different models and systems.

Terminal E is used for safety purposes. This feature is known as Emergency Heat. This helps to shut off the heat pump immediately during excessive heating.

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Thermostat Wiring Diagram with Air Conditioner, Fan, Heat Pump Thermostat Wiring Diagram with Air Conditioner, Fan, Heat Pump Reviewed by Author on May 18, 2019 Rating: 5
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