Your air conditioner should run two to three times per hour for 15–20 minutes when it is working properly. However, several issues can make it run constantly — ranging from a clogged filter, refrigerant leak, faulty wiring, and even a malfunctioning thermostat.
If your air conditioner never shuts off, check out each of these 10 common problems. You can diagnose and fix many of these problems on your own. However, you should consider hiring a local HVAC contractor for a handful of the issues or if you’re not comfortable tinkering around inside your AC unit.
1. Your air filter is clogged.
When it comes to your air conditioner’s efficiency, circulation is critical. Without it, all the dust and debris in a dirty air filter keep your air conditioner from receiving the airflow it needs to cool effectively and then turn off.
Change your filter according to the manufacturer’s directions, usually once every 30 to 90 days, for maximum airflow.
Bonus: A clean air filter will keep dust and allergens from infiltrating your house. A clogged filter prevents proper air circulation through the HVAC system. The evaporator coil can only absorb enough heat from the air with adequate airflow. Consequently, the air conditioner cannot reach the set temperature and disengage.
To keep your system running efficiently, inspect and replace dirty filters once a month during peak cooling season. Use the MERV rating system to select optimal filtration that balances dust removal with airflow.
2. You are running low on refrigerant.
Your air conditioner requires refrigerant to cool the evaporator coils. As your unit ages, leaks are likely to develop, causing refrigerant levels to drop. In some cases, these leaks are slow enough that recharging your refrigerant level is all it takes to improve your air conditioner’s cooling capacity.
The refrigerant circulates through the condenser and evaporator coils to absorb and release heat. With low refrigerant, the cycle cannot efficiently lower the temperature. The evaporator coil will be slightly warm rather than cold, preventing your thermostat from reaching the set temperature and shutting off the air conditioner.
While refrigerant leaks are common as AC systems age, they can also indicate serious problems like a faulty evaporator, condenser, or compressor. Have an HVAC technician evaluate refrigerant levels and identify any underlying issues, such as leaking evaporator coils.
3. Your home lacks insulation.
Your home constantly gains heat from outside sources such as the sun, nearby machinery, and car engines. Proper insulation creates resistance to heat flow and helps your home stay temperate. With inadequate insulation, it takes more work for your air conditioner to overcome heat infiltration and achieve the desired indoor temperature.
If your air conditioner is constantly running, inspect insulation levels around your home, especially in the attic. Then, replace old or missing insulation for maximum energy efficiency. Ensure insulation achieves the recommended R-value for your climate zone. You can even tint windows or install heat-reflective film to block solar heat gain.
4. You have air leaks in your ductwork.
Leaky ducts force your air conditioner to work overtime to cool your home. Sealing ducts is a cost-effective way to boost AC efficiency. Inspect accessible ducts for detachments, gaps, kinks, or punctures. Also, check connections at vents and registers and use mastic sealant or metal tape to patch leaks.
Consider hiring an HVAC technician to perform a duct pressure test for inaccessible ducts. They will seal all vents except one, then use specialized equipment to check for leaks as air flows into the ducts. This process allows them to isolate and repair hidden leaks you cannot access alone.
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5. Dirty Coils, Condenser or Ducts
No one expects their car to run without an oil change, but we sometimes feel like our air conditioners should run without a regular tune-up.
Regular HVAC maintenance is the best way to ensure your unit runs as efficiently as possible. Dirty coils, a dirty condenser, or clogged ducts can contribute to an air conditioner that constantly runs without completely cooling your home.
Fortunately, the solution is as simple as having a specialist perform an HVAC tune-up before summer. They can clean the areas of your air conditioner most susceptible to dirt and recommend any necessary repairs to help you avoid mid-summer meltdowns. Addressing any of these issues can extend the life of your air conditioner and keep you cool all summer.
6. Your AC Unit is Improperly Sized for Your Home
If your air conditioner is too small for your home, it will struggle to keep it cool or bring the temperature down at all. In this case, it will continue to run while it tries to meet the set point on your thermostat. To make sure you get a correctly sized air conditioning unit, hire an experienced HVAC contractor to perform a load calculation.
7. Your Thermostat is Malfunctioning
A malfunctioning thermostat can cause your AC unit to run longer than necessary or never turn off. Thermostat issues like this are uncommon. However, a failed electrical contact can get stuck in the on position, or its internal temperature sensor may incorrectly read a higher temperature.
In this case, your home will become much colder than the desired temperature you choose on your thermostat (assuming everything else is working properly). You can fix this issue yourself by replacing your thermostat — upgrade to a Smart unit for better efficiency and the ability to control from your smartphone.
8. Your AC is Aging and Inefficient
Air conditioners have a life span of 15-20 years. If your AC unit is this old or older, chances are that it is starting to break down. At the very least, it is becoming less efficient at cooling your home. If you have an aging system that is running constantly, I recommend hiring an HVAC company to evaluate and replace it before it fails on a hot summer day.
9. Your Evaporator Coils Are Dirty
If you haven’t been diligent with replacing your HVAC filters, your evaporator coils can become clogged with dust and grime. When evaporator coils remove heat from the air in your home, water condenses on them and normally drips into a condensate drip pan and flows outdoors. However, if the coils are dirty, the moisture can stick to the dust and dirt and create a hard crust.
When your evaporator coils are caked with dust and dirt, it makes it hard to remove heat from your home and your AC unit will run constantly to try to compensate. You can clean your dirty evaporator coils yourself. Remove the access panel on your indoor unit (air handler) and remove the buildup that you can with your hands and a soft tip vacuum attachment. Then, you can use coil cleaner and some water to finish the job.
Coils are delicate, so be careful not to bend or break any fins. If you’re uncomfortable doing this task, just hire an HVAC technician for help instead.
10. Your Ducts are Blocked
Blocked or obstructed ducts can restrict airflow, preventing your air conditioner from effectively moving cool air throughout your home. As a result, your AC may run continuously to compensate for the reduced airflow. Inspect your air vents and registers to ensure they are open and unobstructed by furniture, curtains, debris, kid’s toys, etc. If you suspect blockages within the ductwork itself, consider hiring an HVAC professional to perform a thorough inspection and cleaning.
So, Is an Air Conditioner Running Constantly Always a Problem?
An air conditioner that never shuts off is usually a sign of an underlying issue that needs attention. Identifying and quickly addressing problems will restore cooling efficiency and prevent system failure.
However, it is normal for your air conditioner to run most of the day during stretches of intense heat. I recommend setting your thermostat at a moderate temperature instead of a maximally cold setting to avoid overworking the unit. Ensure your home’s insulation, windows, and ducts are optimized to reduce unnecessary heat gain. Also, replace filters regularly and have an HVAC technician perform seasonal maintenance to keep your air conditioner operating at peak performance when needed.
FAQs About Air Conditioners Running Constantly
Why does my air conditioner freeze up?
A frozen evaporator coil indicates low refrigerant levels or reduced airflow. Lack of refrigerant or airflow prevents the coil from absorbing enough heat, leading to ice formation. Have an HVAC technician check the refrigerant charge and system airflow.
How can I tell if my AC issues are serious?
Warning signs of serious AC problems include strange smells, smoke, dirty air discharge, frequent fuse-blowing, or loud noises from the unit. If you notice these issues, shut off your air conditioner immediately and contact an HVAC professional.
Should I repair or replace my air conditioner?
Consider replacement if your AC unit is over ten years old and experiences frequent breakdowns. Newer AC units are significantly more energy efficient, saving you money on energy bills each month. Reference our guide on the cost of a new unit.
What maintenance can I do myself?
DIY maintenance includes monthly inspecting and changing air filters, cleaning debris from outdoor AC units, and trimming plants and branches blocking outdoor units. HVAC technicians should handle any tasks involving refrigerant, electrical work, or ducts.
How often should my AC be serviced?
HVAC experts recommend professional tune-ups before peak cooling season, generally in the spring. Technicians inspect refrigerant levels, electrical components, condenser and evaporator coils, drain lines, and overall performance. I recommend a fall tune-up to prep the system for winter.
