Why Does My HVAC System Stop Blowing Cold Air When It’s Hot?

In the middle of a sweltering Texas summer, there’s nothing more miserable than a malfunctioning air conditioner not blowing cold air.

It’s an issue that can be avoided with regular maintenance, but even then, unexpected issues may crop up despite your best efforts. Your system may freeze up, overheat, or constantly cycle—and as luck would have it, these issues may occur on the hottest day of the year.

But what can you do when your HVAC stops providing much-needed cold air?

Has Your AC Actually Reached Its Limit?

We’re no stranger to days with the temperature approaching the triple digits. Summers here can be hot. And sometimes, it may seem like your air conditioner simply can’t keep up.

However, this isn’t necessarily a sign that your unit needs to be repaired. On our hottest Texas days, your air conditioner is bound to struggle a bit, especially if you prefer your temperatures in the high 60s to low 70s. Dropping the thermostat lower won’t make it any easier for your AC to compensate for the extreme heat, but that’s not always something to worry about.

If your system does an adequate job of cooling your house in the mornings and evenings but struggles with the midday heat, it may just mean that the Texas summer is a little beyond your system’s capacity.

Air conditioning systems in the Houston area are engineered to hold the indoor temperature to 75 degrees Fahrenheit at a relative humidity of 50 percent when it is 95 or 96 degrees Fahrenheit outside. That calculation is made from an average of how many days engineers expect the outdoor temperature will reach its peak. This is why we like variable speed HVAC systems because it allows us to oversize the system to compensate for those extra hot days.

Don’t forget the best practices for keeping your home cool in the summer. The US Department of Energy offers great resources to help you cool your home efficiently with ceiling fans, window treatments, and more.

Is Your HVAC Not Blowing Cold Air At All?

If your HVAC system isn’t working at all—or if it’s been running non-stop without shutting off—you may have a different issue on your hands. There are a number of issues that might be wreaking havoc with your HVAC, especially as the heat rises. Below are a few common problems to look out for.

Low Airflow

When your AC is working properly, the evaporator coil is absorbing the heat that comes from your warm indoor air. This happens when your air filter is unclogged and can do its job correctly. However, if the airflow is low, or if it isn’t blowing over the evaporator coil at all, none of that heat is absorbed. Instead, the home gets hotter and hotter, and the refrigerant in the coil (which has no heat to absorb) won’t warm up. As a result, the coil will get colder and colder, expanding every time your AC cycles, and it will eventually freeze up and stop working.

The best solution to this problem is to change your air filter at least every three months and as often as once a month, and to use a high-quality filter. Some homes have an additional media filter within the ductwork that is thicker and changed less often – but sometimes people forget about them and they get clogged up, too. Clogged filters can keep your air conditioner from struggling to keep your home cool, wasting energy (and money) in the process.

Another way air flow can be impeded is if the return air vents are blocked by furniture or curtains so they can’t take in enough air. We see this situation more often than you’d think, and it’s easy to fix.

Refrigerant Leak

If there’s a refrigerant leak in your HVAC system, there’s less refrigerant inside the coil where it belongs. Because the total amount of refrigerant in the system is lower than it should be, the pressure in the system is lower. Because the pressure is lower, the remaining refrigerant gets colder. Over time, this can lead to ice forming on the coil and freezing your system.

Note that refrigerant leaks can sometimes be hazardous beyond the problem of a frozen HVAC unit, so it’s important to get this issue taken care of.

Check the vents blowing air and see if it’s blowing cold air or air that is lukewarm. If you’re unsure, you can make sure the copper lines going into your outside unit are not covered with ice, though this will only happen in more extreme cases. Another way to spot ice on copper lines is by looking down past the fan blade into the condenser unit itself for frozen copper lines.

Higher end HVAC systems may have pressure switches which shut down the outside unit if the internal pressure is too low (or too high). If you don’t have enough refrigerant in the system, your system might turn on and off, short-cycling over and over.

Checking for a leak requires special equipment, so it’s not something homeowners can figure out definitively on their own. If an HVAC technician suspects a leak, they may inject your system with a combination dye/sealant, and then return to see the results. Sometimes addressing leaks can be a multi-step problem to fix, but it’s important to find them.

Dirty Condenser Coils

It may seem unlikely, but a buildup of dust, dirt, or other debris on your condenser coils may be all it takes to cause issues with your HVAC unit. Your outdoor unit sheds the heat that has been picked up from inside the house.

However, when dirt covers the coils, it acts as insulation. This insulation makes it difficult for the condenser coils to exchange heat. This, in turn, can cause your air conditioner to overheat.

To solve this issue, check your condenser coils for dirt and debris, and clear away anything that’s accumulated. And keep in mind that the dirt on your coil is not always visible to the naked eye, so when in doubt, wash it out. A garden hose is an easy way to clean it off.

Do not become overzealous about cleaning your condenser unit with water on a weekly basis. Because the water in our area is hard, it has a lot of dissolved minerals that can calcify on the fins if you wash it too often. Once or twice a year is the perfect frequency for cleaning your condenser – unless you have extenuating circumstances.

Mechanical Issues

Sometimes, problems that at first seem minor can build up to more serious HVAC problems. For example, a fan may be broken or dented enough to strike another piece of equipment, or minor damage or dents in the outside condenser may cause the pressure to change within the coil. Maybe a mouse got into the electrical panel and chewed through some wires without you knowing about it.

Subtle issues like these are trickier for homeowners to diagnose, but a specialist can do a thorough HVAC inspection of your system to root out any minor problems. Electrical parts like fan motors and run capacitors sometimes wear out, and they are often not expensive to fix.

What to Do if Your AC Is Not Blowing Cold Air

First, observe if it is blowing air at all in the house.

Check the outside condenser unit next. Is it blowing hot air when it is on, or does the air it’s blowing seem cooler than usual? If it’s cooler, it could be in need of refrigerant or the compressor has gone out.

Then, turn your system off at the thermostat.

Before you do anything else, try changing the air filter. This will help you figure out whether the issue is simply low airflow due to a clogged filter. Don’t forget to also move anything else that might be blocking the airflow, such as curtains or furniture.

Next, try cleaning the condenser coil to make sure it’s free of any dust or debris if this hasn’t been done in a while.

If all else fails, make note of what you’re seeing and hearing from the unit.

Is it constantly cycling, or is it coming on and then shutting off immediately? Is it blowing hot air into your home, or is there no circulation at all? Are there strange noises or signs of leakage?

Information like this can help you describe the issue in full when you call for an HVAC technician, and it can also help them think about possible causes in advance of their arrival.

Call For Expert Backup

Don’t sit in the sweltering heat! If these tips don’t work, it’s time to call for expert help. We’re standing by to help you rule out some of the most common AC issues and to help get your HVAC blowing cold air again. Contact us at 281-495-7830 to schedule an HVAC service call in the Southwest Houston, Katy, Richmond, Fulshear, and Weston Lakes area. As a Carrier Factory Authorized Dealer, we service all makes and models of equipment and guarantee our work. Find out what our customers say and why they choose our company for reliable AC service.