Blog>Expert Advice>What to do when your air conditioner won't switch on
Last updated: 13 June 2024
What to do when your air conditioner won't switch on
Don't lose your cool if your air conditioner won't switch on. Read our helpful troubleshooting tips and find out what to do if your ac unit is struggling to work.

During a warm spell, it can be a real nuisance if your air conditioner won't switch on.
Will you need a brand new AC unit? Or could it be the case that a repair job could get your air conditioner working properly?
Don't lose your cool just yet and resign yourself to a repair or replacement. First, read our useful troubleshooting guide if your air con is struggling to start.
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Why is my air conditioner not turning on?
An AC unit not turning on can get homeowners hot under the collar for more reasons than one.
From tripped circuit breakers to grubby air filters, there are several common reasons why your air con won't switch. And in some cases, you might be able to fix the problem yourself. Read on for reasons why your AC won't turn on - and what to do about it.
Troubleshooting: AC unit not turning on
These six troubleshooting tips could get your AC unit back to good health in no time. But if in doubt, don't hesitate to call in the experts.
1. Check the thermostat
First, check the thermostat batteries, and if they're dead, replace them.
If the batteries are working, make sure your thermostat is in cooling mode and the temperature is set a few degrees lower than the indoor temperature. The thermostat may have accidentally been switched to 'off' by someone in the family.
If your thermostat is set to cool but the AC is not turning on, it's likely your thermostat is broken and needs replacing. Get in touch with an AC professional who can help.
2. Check the air filter
Dirty air filters can clog up your AC unit, causing your air conditioner to freeze and not turn on.
To prevent this issue, filters need regular cleaning - you should also aim to replace them every couple of months.
You might need to swap filters more regularly depending on the number of pets and people living in your home and local air pollution levels.
If your AC was frozen, wait for it to thaw after changing the filter before turning it back on.
3. Check the circuit breaker
If your thermostat is set to cool but the AC is not turning on, check the circuit breaker. A tripped circuit breaker could be the issue.
To resolve this problem, open the electrical panel inside your home and check if any of the breakers have accidentally tripped. Simply flip the switch so that it's in the ON position. Then check to see if this fixed the issue.
If your AC continues to trip the breaker, it could be a bigger problem. It's recommended to get in touch with a professional HVAC (Heating, Ventilation, and Air Conditioning) company who can assess the problem.

4. Check the indoor shut-off switch
If your AC unit is not turning on, the indoor power switch might have been accidentally flipped to the OFF position.
Your AC shut-off switch looks really similar to a light switch, so it's a good idea to label it to prevent any mistakes in the future.
For more information, check out our guide on everything you need to know about air conditioning.
5. Check the outdoor shut-off switch
If the outside AC unit is not turning on but the inside is, it's time to check the outdoor shut-off switch.
The emergency shut-off switch is usually located next to the outside AC unit in a metal box. If you or someone else has recently worked on your air conditioner, they could have turned off the external shut-off switch as a safety precaution.
If the switch is in the OFF position, simply flip it to get your air conditioner to turn on.
6. Check for a build-up of ice
If you find ice on your machine - either on or inside the unit - wait for it to defrost before restarting the system.
There are several reasons for a build-up of ice including a thermostat set too low, dusty filters, low levels of refrigerant, or a blocked coil. If you do see ice on your air conditioner, we recommend getting this investigated as soon as possible by an experienced air conditioning specialist.

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Find a local air conditioning repair expert
If these helpful tips and possible fixes haven't resolved the issue, it's time to call an air conditioning expert.
Unless you’re qualified and experienced in handling air con repairs, we recommend you find a trusted air con specialist to get a bespoke quote to suit your needs.
We always recommend getting a minimum of three quotes for any job or service. This means you can compare what’s included as well as the price.
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FAQs
How do you reset the AC when it is not turning on?
Look for a reset switch on the outside unit - push it and see if it helps.
If your unit doesn't have a reset button, you can manually reset your air conditioner by switching the thermostat off for 5 - 10 minutes before turning it back on again.
This is generally only a temporary solution and you'll need to get a professional to inspect the unit to identify why your AC unit is not turning on.
How do I force my AC to turn on?
Most air conditioning units are equipped with a reset button - they tend to be red and quite small. Consult your owner's manual if you're having a problem finding it.
Hold down the reset button for 3 to 5 seconds and then release. Your air conditioner should start up.
Place your hands by the vents to check cold air is blowing through the ductwork.
If the AC doesn't start operating, press the button again for an extra three seconds. If it's still not working, it's time to call in an air conditioning expert who will diagnose and fix the problem.
Is air conditioning expensive to run?
As a rough guide, the running cost of an air conditioner unit can range from 10 pence to 25 pence per hour of operation.
However, several factors can affect how expensive it is to run air conditioning in the UK.
Just a few of these include:
The type of AC unit
Its age
How long it's run for
Its efficiency
How well insulated your property is
By coupling your air conditioning unit with other measures – such as sealing your windows to keep cool air in, investing in a smart thermostat, and properly maintaining your air conditioner – you can reduce your running costs.
An air conditioning engineer will usually charge around £30 - £60 per hour to service or regas an air conditioning unit, plus the cost of the refrigerant, which is typically between£35 - £130.
With that in mind, you can generally expect to spend around£70 - £120 per unit onair con servicing costs.
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