Do you understand how the control circuit of your air conditioning works? You might think that this is not important – but the truth is, this knowledge will help you care for your air conditioning unit better. We all know that proper maintenance is the key to increase the lifespan of your system. It will help you save money and will even make it energy efficient.

Like any system that runs on electricity, there is a sequence that happens to make it work properly. You need to understand the controls so you can follow how the sequence works. This will help you identify the important parts that have the most potential to compromise the functionality of your air conditioning unit.

So what should you know about the control circuit of your air conditioner at home? What happens the moment you turn the thermostat on?

Two important aspects of the control circuit

Transformer

Let us start with the transformer. In an AC unit, the transformer is the one that brings down the level of voltage that comes from the source of electricity. For instance, most AC units only need 24 volts to run. But the voltage coming from electrical outlets are usually 120V or 240V. Without the transformer, your air conditioning unit will be fried immediately after you turn it on. The transformer ensures that only the correct voltage will enter the system. Make sure you know the VA rating of the control transformers to ensure that it can give your unit the right voltage.

Now the relay (also known as load) that is in the control system has a VA rating. Make sure that the sum of these VA ratings will not exceed the VA rating that is indicated on the transformer. If it does, it will affect the control circuit of the AC unit. It will not work and the transformer will fail. You should also make sure that the inline fuse is located on the 24V hot side of your unit’s transformer. This will protect the transformer from blowing in case there is a dead short in your control circuit.

Relay and contactor

We mentioned the relays. What exactly are these? The relays and the contractors that are used in your AC unit control circuits are responsible for turning different parts on and off. These include the blower motor, compressor, or condenser fan motor. The different parts are powered by 24 volts (usually). The line voltage is passed to these compressors or motors to make it work.

It is important to ensure that the coils and contacts of the relay and contractors receive the right amount of voltage (coil) or amp rating (contact). Otherwise, the high voltage load will blow out the coil or contacts. A 120 voltage will blow out a 24V coil while a 10 amp rating will burn out a contact with a 5 amp rating.

In case this happens, the relay or contractor will have to be replaced. If so, make sure that you replace it with the same voltage or amp rating.

How it works together

Now that you understand the transformer and the relay or contractor, let us discuss how all these make your air conditioning unit work.

The relay or contractor is the one responsible for turning the AC unit on or off. It is the switch that makes the motor or compressor running. It is part of the 24V control circuit. Depending on the specific components of your air conditioner, it is possible that some of your relays are controlled by other relays. This affects the overall system and the sequence of operation.

When you turn the AC unit on through the thermostat, the voltage from the energy source will flow through the transformer. The transformer will ensure that only the right amount of voltage will enter the circuit. From the transformer, the voltage will run to the 24V neutral leg then go to the side of the coil that is attached to it. When the thermostat is on, that means it closes the 24V hot leg to complete the circuit. The coil is energized and in effect, closes the contacts and turns on the blower motor. This will get the air conditioning unit running.