A power outage by itself won’t damage an AC unit and cause it to stop working. Rather it’s the events leading up to the power outage which can cause the damage. This can include a voltage spike or loss of electrical phase. This post will discuss why the AC stopped working and what can be done about it.
AC Wiring & Fault Finding
A split AC system typically contains two components, the indoor and outdoor unit. Power to the AC unit is controlled by an isolator or switch which can turn the AC unit on and off.
An AC unit should be on an independent circuit. This means that there will be a dedicated circuit breaker in the switchboard for this circuit. For the wiring, a wire goes from the AC unit to a switch or isolator. From the switch the wire goes to a circuit breaker in the switchboard.
At the switchboard, the circuit breaker for the AC unit will most likely be labelled as ‘air conditioning’ or something similar.
This circuit breaker (MCB) protects the cable if a short circuit or overload fault was to occur.
The circuit breaker rating will depend on the heating/cooling capacity of the AC unit. For many domestic units the circuit breaker will be rated at 20 amps but could be smaller or larger.
The AC unit is most likely not protected by an RCD (residual current device) as access to electrically live parts which can give someone a shock is impossible without a tool.
The purpose of an RCD is to protect anyone from getting a shock which is fatal or causes long term harm
With the basic wiring of an AC unit covered, let’s look at why it’s not working after a power outage.
AC Stopped Working After Power Outage? – Reason #1
Electrical Feed Containing The AC Unit Is Still Out
Likelihood: Moderate
Typically a home will have either single phase, two phase or three phase power supply. To check what you have you will want to look at your power meter. If you have a digital meter, it will give an indication how many phases you have with LED lights.
If you have double or triple sized circuit breakers in the switchboard (excluding RCDs or residual current devices) that would indicate you have two or three phase power.
In simple terms, single phase means you have one feed into the house from the power company. Two phase power has two feeds and three phase power has three feeds. Sometimes a power outage results in losing one feed rather than all three feeds.
This results in a partial power outage.
In this case, I suggest that the AC unit is on a feed which is currently still down.
In electrical terms this is called a ‘lost phase’ which can cause other problems to the AC unit if it is a big three phase unit as detailed below.
AC Stopped Working After Power Outage? – Reason #2
Lost Phase Causing AC To Burn Out
Likelihood: High – if the AC unit needs three phase power. Ignore if the AC requires single phase power.
If the AC unit requires three phase power then losing a phase due to a power outage can cause damage to the unit. This occurs because the AC unit tries to compensate for the lost power feed by drawing more current from the remaining power feeds. This imbalance generates more heat and eventually burns the unit out causing it to fail. When this happens you may notice that the AC unit was making weird sounds for a while. These sounds can make it seem like the AC unit is struggling before eventually failing.
AC Stopped Working After Power Outage? – Reason #3
Voltage Spike Damages The Electronics Inside The AC Unit
Likelihood: High – common occurrence with power outages in our experience.
A voltage spike can be a common occurrence with power outages. A voltage spike will damage components inside the AC unit including capacitors, windings, and any other semiconductor and electronic components. If the voltage spike is high enough the voltage can ‘escape’ the insulation on the wire causing complete damage to the AC unit. If a voltage spike is the cause you should be covered by your home insurance.
Electricians Perspective
A voltage spike causing damage to the electronic components inside of the AC unit is the biggest reason why it isn’t working after a power outage. A voltage spike is a common occurrence and can be prevented by installing spike protection in your home. As most household components have some form of electronics which can be damaged by spikes, it is a good idea to install this to avoid a huge replacement bill.
A lost phase is another common reason but only if your home is on two or three phase. If your home was only on single phase you’d still have no power to everything in the home.
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