Stay Comfy Blog

How Do Hot Days Affect My AC Unit?

hot days affect ac unitHave you ever felt a little sluggish when working in the yard on a 90-degree day? Did it require more work to get the job done because of the heat and humidity? It most likely did. And the same is true for your air conditioner. In fact, heat, humidity, and airflow have a lot to do with how hard your AC unit operates.

So, here's exactly how the heat affects your AC unit.

The Heat

An air conditioner is essentially a heat transfer system with two heat exchangers, working with heat in two environments. First, it captures heat-energy from the warm air inside the house and sends it to the outdoor condensing unit, and secondly it has to reject that heat–energy to the hot outside air. On hot days, that means your AC unit needs to work doubly hard. Not only is there more heat coming into your home (i.e. sun through the windows, air through seams in windows and doors), which it needs to remove, but also the air outdoors is hotter, which makes it harder for your AC unit to reject the heat.

Think of it as the dance of equilibrium. It’s easier to work together when the two environments are tangoing comfortably around the same temperature (that’s when you don’t need your AC). But when the heat is on, it’s much harder to make the indoor environment cooler than the outdoors. One environment wants to do a cool swing dance and the other is doing a steamy salsa — so your AC has to work that much harder to find the same rhythm. And the bigger the difference, the harder it needs to work.

“It’s all a matter of temperature difference. It’s a lot easier to reject heat to warm air at 80 degrees than it is hot air at 95 degrees,” says Keith Hill, technical support manager at Minnesota Air.

The Humidity

Not only does heat affect how your AC performs on a hot summer day, but humidity plays a major role, too. An excessive humidity level means your AC will be working harder to get rid of that damp, clammy air. And if your AC unit doesn’t have the cooling capacity to handle it, you will feel and see the results (frizzy hair, sweating, clammy skin).

The Airflow

Another factor that determines how efficiently your AC unit works is airflow. Your air conditioner’s performance is dependent on proper circulation of air throughout the system. When that circulation is interrupted or blocked, it can cause your AC unit to work harder to provide the cooling comfort you’re looking for. Watch for some typical ways your unit’s airflow could be compromised.

Plants and shrubbery near your outside condenser can be one cause of blocked airflow. Check throughout the season that your landscaping isn’t encroaching on the condenser and take the time to trim trees, shrubs, and flowers that may be growing too close to the unit. A good rule of thumb is to keep a clear space of at least one foot all around the unit.

Be mindful where your unit is located. “We see many units that are installed under a deck," Keith says. "Even though the deck is open on two or three sides it will still cause much of the hot air to be captured and drawn back into the inlet of the unit causing the unit to operate at much higher temperatures." The resulting higher temperatures cause the internal refrigerant pressures to climb and the compressor to run much hotter than it’s designed for.

Poor airflow also causes elevated temperatures of the lubricating oil inside the compressor, which may lead to a breakdown of the oil. It’s similar to your car engine running at very hot temperatures. You need to change your car oil more frequently to prevent engine wear. However, the oil in AC units is never changed; it’s designed to run for the life of the unit —typically 15 to 20 years — assuming your unit is properly maintained and operating with adequate airflow.

If you think you may have an airflow issue, you can easily check it with a simple thermometer. On a calm day (wind may give you a false negative), run your AC and check the air temperature an inch or two away from the inlet. It should be the same temperature as the air 20 feet away. If the entering air temp is higher, then you have a recirculating problem.

The Equipment

Keith says don’t worry about wear and tear on the unit in hot weather. It’s made to take it, as long as it is well maintained and operating at peak performance.

“Dirty condenser coils combined with hot weather — that’s when you get your wear and tear,” he says. “The internal operating pressures and temperatures in those conditions far exceed normal operating limits. If the unit operates like that for an extended period of time, the oil will overheat. Burnt oil is a poor lubricant and it’s acidic, so a snowball effect ensues, and the compressor ultimately fails.”

To see how you can clean your AC coil, click here. And remember, if you are in the market to buy a new AC unit, pick one that suits the size of your home. Bigger is not better in this case — picking the proper size is most effective. If it’s too big, it won’t remove moisture from the air as effectively because it won’t need to run as much, giving it less time to dehumidify your home.

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