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7 reasons why your AC isn’t cooling your home

A malfunctioning AC can make your home feel incredibly uncomfortable. Today’s HVAC and cooling systems are smarter and more efficient, but sometimes things still go wrong, especially if you have an older air conditioning unit that may not be operating at its best (and could be costing you a lot of money). If your home is staying too toasty no matter what you do with your thermostat, we have a few suggestions for what to look at.

Clogged filters

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Home AC units usually have a primary filter that’s located close to the fan in the duct system. These filters are, in most cases, disposable and need to be replaced from time to time.

When filters are forgotten and left in too long, they start to get clogged with dust. This slows down airflow, which means that cooled air cannot spread throughout your house like it’s supposed to, even with the AC unit running. You don’t get cool air, and your system has to work a lot harder than it should. Fortunately, it’s easy to check on your filter and replace it if necessary.

When buying new filters, make sure you get the proper size, which is marked on the individual filter. You can find packs of them at any department or home supply store. The filters will also have arrows on them, designed to face the same way that air is flowing in your ductwork when you place the filter. A little practice and this simple step becomes effortless.

Dirty, crowded outdoor units

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Larger home cooling systems have an outdoor condenser unit. This is the part of the heat exchanger that releases the heat stored in the refrigerant as it is moved out of the home (condensing the refrigerant back into a more liquid form). Condensers are durable, but being outdoors from season to season can take its toll. If your air conditioner isn’t cooling right, it’s a good idea to head outside and check on your condenser.

First, make sure any debris is cleared away from the unit. If bushes or tree limbs have grown near the condenser, clear them away. The unit needs plenty of open air to work efficiently.

Second, take a close look at the condenser fins, or the grill-like section that’s designed to help heat dissipate in the air. If these fins have a layer of dirt on them, they can’t perform effectively anymore. A cloth, some warm water, and a light cleaner can have them back in operation in no time.

Note that this also applies if you have a heat pump — the big difference is that a heat pump can reverse the process to bring heat inside the house as well as cool it down.

Ductwork problems

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Ductwork comes in many forms, but it all works to channel cooled (and heated) air to rooms throughout your house and allows air to flow back via vents so the air conditioner can continue its work. If you’ve ever heard the term “air balance,” it usually refers to how ductwork and vents move air around a home.

Unless you have a single-room AC unit, ductwork is a key part of the system, and problems can prevent your house from cooling properly. Cracks, gaps, or missing sections of ductwork mean that cool air isn’t making it to the right rooms, and your AC probably isn’t very effective.

The challenge is that ductwork isn’t exactly visible. You can check to make sure your vents are unblocked, but what if there’s a probably deeper down? One of the most effective ways to check is with a two-person team. One climbs into the basement/attic/crawlspace to look at the ductwork while the other shines a flashlight into the vents. Seeing cracks of light is a good sign your ductwork is cracking and needs repairs or replacements.

Refrigerant issues

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The refrigerant in an air conditioning unit is a closed system — it isn’t used up in the same way that fuel is. However, over time, small amounts of refrigerant can leak out. An air conditioner low on refrigerant will start running for longer periods of time without being able to cool down a house effectively.

The best way to see if this is a problem is to arrange for a maintenance visit from a technician who can measure current refrigerant levels and add more of the correct kind of refrigerant if necessary. This is one situation where you can’t really tell the source of the problem just by looking at the air conditioner, and testing refrigerant is best left to a professional.

Problematic thermostats

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This happens a lot with older homes and old thermostats that slowly stop functioning over time. Mechanical thermostats, in particular, can encounter sensor problems that make it difficult for them to properly sense the temperature accurately, which in turn leads to unpredictable AC results.

That’s why we highly recommend switching to one of today’s great smart thermostats if possible. Brands like Nest thermostats and Ecobee thermostats are accurate, durable, and can help you save money on energy bills without too much extra work.

A poorly-sized AC unit

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This isn’t as common of a problem, but it’s worth noting if you recently completed a remodeling project or bought a new house. This can be particularly problematic if you recently turned a non-air conditioned space, like a screened-in porch or garage, into air conditioned living space. HVAC units are sized and designed to manage a specific amount of air for a certain-sized area. If you get an air conditioner that’s too large and powerful for your home, it’s going to frequently shut off and struggle to keep things reliably cool. If your AC is too small for your house or has become too small because of a recent renovation, it will work too hard without being able to cool things down.

Some AC units will have sizing information right on their info plate next to their efficiency ratings or will at least have a serial number you can look up online more for information. Compare this with the square footage of your home. This is a great guide for learning more.

Trouble with house heating

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Sometimes the air conditioning is working fine, but mistakes with managing house heat sources can counteract cooling, leaving you with less-than-impressive results. Try turning good practices into habits, like:

  • Open up windows at night to cool down, but make sure windows are closed by the morning so warm air can’t get inside. Use shades or drapes to keep sunlight from adding any unnecessary heat to your home during the day.
  • If the weatherstripping (the felt lines on the edges that help with sealing) on your doors and windows is worn down, hot air can leak in. Replace any worn or missing weatherstripping.
  • Keep exhaust fans in the kitchen and bathroom running for a bit after you’re finished to draw up excess heat along with steam.

Remember, some of these issues can be difficult to diagnose on your own, and some can’t be fixed without professional help. If you notice a problem, it’s a smart idea to start searching for a well-rated local HVAC service and get in touch with a technician. Summer months can be busy times for AC experts, so you may want to schedule an inspection ahead of time. A maintenance inspection every couple of years can also help prevent problems.

Tyler Lacoma
If it can be streamed, voice-activated, made better with an app, or beaten by mashing buttons, Tyler's into it. When he's not…
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