Electrical Why do my lights dim when the air conditioner starts?
A brief dip when a big appliance starts can happen, but dimming that is getting worse, lasts or comes with other signs needs a licensed electrician.
Lights can dim briefly when an air conditioner starts because it draws a surge of power for a moment as its motor kicks in. A short, small dip that stays the same may not be a concern. Dimming that is getting worse, lasts longer, or comes with tripping, buzzing or heat should be checked by a licensed electrician.
Why does starting an air conditioner affect the lights?
Electric motors need more current to start than to keep running. When an air conditioner’s compressor starts, it briefly pulls a large amount of power, which can pull the voltage down for a moment. Lights on the same circuit, or sometimes the same part of the home’s wiring, show this as a brief dip.
How noticeable it is depends on the size of the air conditioner, the wiring, the connections, and how many other things share the circuit. A small, brief dip at start-up can be normal, but the same effect gets worse if something is wrong behind the scenes.
What can make dimming worse?
In general terms, the causes electricians look at include:
- the air conditioner sharing a circuit with lights or other appliances
- wiring that is too light for the load it now carries
- loose or deteriorating connections, which resist the flow of current and generate heat
- a supply issue at the home’s connection to the street
An air conditioner would normally be installed on a circuit of its own, so that it is not sharing with lights. If lights dim sharply, or the dimming has started recently or is changing, that may point to a fault, not a normal start-up effect.
Is it my home or the street?
If lights dim in neighbouring homes at the same moment, or flicker at times unrelated to your air conditioner, the cause may be on the network. Report that to your network provider’s faults line.
If the dimming only happens inside your home and lines up with the air conditioner starting, that points to the home’s wiring and load. Diagnosing it involves testing the circuit and its connections, which is electrical work. In Queensland, electrical work must be done by a licensed electrician, and the Electrical Safety Office Queensland is the regulator.
What if I am planning a new air conditioner?
If you are adding or upgrading an air conditioner, ask the installer or a licensed electrician whether your switchboard and wiring suit the extra load. Older boards and circuits are sometimes not suited to large new loads, and an electrician can advise before problems show up.
What to note for the electrician
When the dimming happens
Write down whether it only happens at start-up, or also while the air conditioner is running, and how long it lasts.
Which lights and rooms
Note which lights dim, and whether other things, such as the fridge or a television, are affected as well.
Other signs
Record any tripping, buzzing, visible scorch marks or smells. Do not touch anything to check.
The air conditioner details
Copy down the make, model and approximate age from the indoor unit label if you can see it, and when it was installed.
Frequently asked questions
A brief, small dip can happen because the motor draws extra current at start-up. If it is getting worse, lasts longer or comes with other signs, have a licensed electrician look at it.
Repeated large voltage dips are not good for electronics and may signal a connection problem. A licensed electrician can find the cause.
Air conditioners are normally installed on a circuit of their own. A licensed electrician or your installer can tell you what suits your system.
If neighbours see the same thing, tell the network provider's faults line. If it only happens in your home, contact a licensed electrician.
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