Reasons Why AC Won’t Cool Below 80

Either it is so hot outside that the air conditioner can’t keep up – or there’s something wrong with your AC. You have the thermostat set below 80, right? OK, let’s get on with it then. 

In hot weather, and the AC isn’t doing its job, we start searching online with phrases like – air conditioner not cooling house below 80. Or something like that. 

Well, we’ve got possible solutions. Some might work. Others won’t. Some you can do. Others are best handled by an air conditioning professional.

Read on to find out why “air conditioner not cooling house below 80.”

Is the Outdoor Temperature More Than 5 Degrees Above Design Temperature?

This is a technical way of saying it might just be too hot for your AC to handle.

Time-saving tip from Pick HVAC: If your current weather is not abnormally hot, and you want to find a potential solution to your ACs mechanical issue, skip to the next section.

However, if it is hotter than usual for your area, it might not be your air conditioner. The extreme heat outside might be the reason the air conditioner can’t keep up on hot days.

And this section will explain what’s going on.

What is design temperature? Every county in the country has a designated “design temperature.” As you might guess, design temperature is the outdoor temperature that an HVAC system is designed for. The hotter your climate, the higher the design temperature. The design temperature is the temperature your climate rarely exceeds. If it exceeds it more than 1% of the time, then the HVAC industry raises the design temperature of the area. They use 30-year data to set design temperatures.

For example, Maricopa County in AZ, home to Phoenix, has a design temperature of 111 degrees, which means that the outside temperature exceeds 111 degrees 1% of the time – or less. Here are design temperatures for every county in America.

The first thing to do is to find your county’s design temperature. 

What is the temperature outside? What is the design temperature for your county? 

>If the design temperature is higher than the temperature of the outside air, skip to the next section covering potential mechanical reasons your AC can’t keep up. 

>If your current weather is hotter than the design temperature, then your AC might not be large enough to handle that much heat. Use a fan for now, and plan to buy a larger AC or upgrade the capacity of central air conditioning when possible. Putting a single-zone mini split system in the hottest area of the house will help too. 

Mechanical Reasons your AC Can’t Keep Up

If the outdoor temperature isn’t more than 5 degrees above design temperature, here are 10 Reasons your air conditioner can’t keep up  – Ranked in possibility from high to low

If you’ve eliminated extreme heat as the reason for the air conditioning not cooling the house below 80 or wherever you want it, then consider these.

1). Thermostat Settings – Sometimes the thermostat isn’t set where we think it is set – or someone changes the temperature and we don’t know about it. For example, you might think the thermostat is set to 72 degrees, but it might be set at 82 degrees.  

2). A Dirty Air Filter – If the air filter is dirty, it hinders airflow and the ACs ability to remove heat and cool your room or home. Change the air filter, and see what happens. Tip: It’s OK to run an AC without an air filter for a few hours if you don’t have a replacement. But get a new one ASAP. 

3). Low Refrigerant – If the air conditioner is low on refrigerant, it can’t properly cool the air. The refrigerant has leaked out. The leak needs to be found, and the system recharged. Don’t wait on this one. A system with low refrigerant will work really hard, trying to keep up. The result is that low refrigerant can lead to the compressor overheating and/or burning out. 

4). Leaky Air Ducts – Leaky air ducts will allow cooled air to escape in the ductwork before they reach the intended vents. This will cause the air conditioner to not be able to reach the desired cool temperature. Leaky air ducts will also cause your air conditioner to work harder than normal, which will also lead to higher energy costs and possible mechanical failure. Here is a guide to teach you how to check leaks.

5). Dirty Condenser Coils or Evaporator Coils – Dirty coils make it more difficult to transfer the hot air from inside the home to the outside. Hire an HVAC technician to give the system a thorough cleaning, or DIY.

6). An Undersized AC – A standard measurement to help determine if an AC unit is large enough is that 12,000 BTUs will cool around 500 square feet. If your home is 2,000 square feet then your air conditioner has to push out at least 48,000 BTUs. An HVAC pro can quickly determine whether this is the issue. If the AC is new and has “never” done a good job on the hottest days, this is a likely cause. 

7). Undersized Duct with Excessive Static Pressure – You can’t blow much air through a straw, right? If the ductwork is undersized, the airflow will be restricted. Signs of undersized ductwork are the following: loud airflow and strange noises, like whistling and popping. Static pressure will also restrict the airflow, which will cause your AC unit to work harder to compensate for the poor airflow. This will lead to higher energy costs. This is another diagnosis best left to an air conditioning technician. 

8). Unbalanced Duct Design with Hot and Cold Spot – If a home has hot and cold spots, this is likely caused by an unbalanced ductwork design. The ductwork is not the correct size and not properly installed in the home. This leads to some rooms getting too much cool air and other places getting not enough cool air. Overall, this makes it impossible for your AC unit to achieve the same desired temperature throughout the home. 

9). Bad Thermostat – A bad thermostat might communicate bad information to the AC, and the unit won’t start cooling or will shut off too soon. Sometimes the thermostat battery just needs to be replaced, but other times the entire thermostat will need to be replaced with a new thermostat. 

10). Bad TXV – The TXV (thermostatic expansion valve) is a device that regulates the rate of flow for the refrigerant in an air conditioning system. If the TXV fails to work properly or goes “bad”, then the refrigerant won’t circulate in the volume it should – and it is refrigerant that captures heat indoors and carries it outside to get rid of it.

What Can You Do to Improve Your AC Cooling Capacity?

Try these to get the best from any air conditioner or system: 

1). Change Air Filter – If it looks really dirty or it has been 3+ months, replace it. This is a very easy and cost effective way to improve the cooling capacity of your AC unit.

2). Clean Coils – If the coils are dirty and need to be cleaned, then the AC unit will have a reduced ability to transfer the heat to the outside. This will result in your AC unit operating at a lower efficiency level. Studies have shown that even 1/100” of an inch of dirt on coils can drop the cooling efficiency by around 5%. This will lead to lower cooling ability and higher energy costs.

3). Add Insulation – When most people think about insulation, they think it is for keeping a home warm and comfortable in the colder months. However, insulation is just important to keep your home cool in the warmer months when your air conditioner is operating. Without insulation, both cool and warm air can escape the home, which leads to higher energy bills and less efficient heating and cooling.4). Add Blinds – Look for thick blinds – some are advertised as having insulation value. They will prevent sunlight from heating up the air in your home.

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

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