Why is my AC not blowing cold air? — here's what HVAC experts say

Tom's Guide

18-05-2025

As the weather warms up, most homes are already blasting their air conditioners to keep cool, comfortable and of course, sweat-free.
But if you're still feeling hot, you're probably wondering why your AC isn't blowing cool air? Like most systems around the home, even the best air conditioners need regular care and maintenance to get the job done.
After all, the last thing you want is for your unit to break down in the middle of a sweltering heatwave!
Luckily, we've called on the HVAC experts to explain the possible reasons why your AC is not blowing cool air, and top tips.
One common cause is a clogged filter or coil, which can have a build-up of debris over time, restricting airflow.
'In most cases, the problem is caused by something like a clogged filter, or a clogged coil, which you can fix yourself in a few minutes', advises Justin Cornforth, owner and CEO at Ace Home Co.
'A clogged coil can stop your AC from blowing cold air but is quite easy to fix. Just turn off the power to the unit and rinse the outdoor coil with a garden hose from the inside out. No scrubbing or special cleaner needed, just plain water washes the dirt away pretty well.'
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Similarly, dirty or clogged filters need to work twice as hard in a heatwave, which often results in not running more efficiently or at worse case, breaking down.
'When it's clogged, airflow gets restricted and your AC struggles to do its job,' adds Glenn Wiseman, Manager at Top Hat Home Comfort Services.
'Changing your filter every 1–3 months, keeping the outdoor unit clear of debris, and having a professional maintenance check once a year can prevent a lot of the issues we see in emergency calls.'
This might seem like a no-brainer, but the first thing you should check is your thermostat settings.
'Check your thermostat settings first,' adds Wiseman. 'You'd be surprised how many calls we get where it's accidentally set to 'fan' instead of 'cool.' Next, inspect your air filter. If it looks gray and packed with dust, it's time for a change.
Essentially, once the outside temperature reaches past 194 degrees F, your system has to work hard. And so the closer the indoor temperature is to the outdoor temperature, the more efficiently your AC will work.
What's more, if you have one of the best smart thermostats, this gives you the flexibility to control the thermostat remotely from your smartphone. Smart air conditioners can also be connected to Alexa and Google Assistant, so that you can create automations around your home.
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Another reason why your AC isn't blowing cool air is low refrigerant levels. Essentially, refrigerant is the substance that your air conditioner needs to remove heat from the air inside your house.
Not only does low levels cause your AC to work even harder, but it uses up more energy in doing so.
'Another cause could be that the refrigerant, the fluid that cools the circulating air inside, is low or leaking,' states Lucy Arnold, Service and Maintenance Manager at PRA Air Conditioning.
'The less refrigerant in your AC, the warmer the air it blows out will be. Over time, leaks can damage the unit, leading to costly repairs, so if you notice hissing noises or ice on the refrigerant line, turn it off and contact a HVAC expert.'
It's important to keep your outdoor condenser unit clear of debris and dirt to ensure it isn't blocked and runs efficiently.
'Spray off the outside unit with a hose to clear out leaves and dust every now and then,' advises Cornforth.' Plus, schedule a professional check once a year, preferably before the start of the cooling season.'
To clean your outdoor unit thoroughly, you can use a special cleaning solution that can be bought at your local hardware store or online. This works well to easily lift and remove stuck-on dirt and grime. Just always use with caution, and keep away from children and pets.
'Also, don't ignore small signs,' adds Wiseman. 'If the system is making strange noises, running longer than usual, or not keeping up on hot days, that's your A/C waving a red flag. Catching issues early is always cheaper and less stressful than dealing with a breakdown in July.'
For more cleaning tips, here's how to clean an air conditioner and keep it running like new.