Is your AC blowing hot air? That’s the last thing you want on a hot summer day. But no sweat! Our HVAC techs share four common reasons your AC is not cooling properly (and what you can do about it!)
The most common reasons your AC is blowing hot air:
- Your thermostat settings are incorrect
- There’s an issue with your outside unit
- Your system has a refrigerant leak
- Your evaporator coil is dirty
There are other possible causes as well. This isn’t meant to be an exhaustive list (it would make this blog way longer than you’d care to read). Besides, the chances are high that your issue is one of these four. Let’s dive in to find out what’s up with your AC!
1. Your thermostat settings are incorrect
Because the thermostat is the brain of your air conditioner, it’s a good place to start! There are two settings to check when you’re having a warm air issue. Head over to the thermostat and make sure:
- The thermostat is set to “cool”
- The fan setting is set to “auto”
Let’s check out why it matters.
Make sure your thermostat is set to “cool.”
This might sound obvious, but when you’ve got kids headed to baseball, the boss is calling, and dinner’s on the stove, the “heat” to “cool” switch can get lost in the shuffle. If you need to, change the dial to “cool.” You have our permission to pretend it never happened.
But what about the fan setting? Why does it need to be on “auto?”
Make sure the fan setting is on “auto.”
When your air conditioner fan is set to “on”, the AC blower fan (located in the indoor air handler unit) blows nonstop, whether the system is cooling or not. Between cooling cycles, the fan blows uncooled air into your home. When the fan is set to “auto”, the blower fan only runs when the AC is actively cooling. Switch it to “auto,” and you should be good to go.
So, was your warm air issue a thermostat setting? If “yes,” you’re done! But if it wasn’t, we’ll check the outdoor unit next.
2. There’s an issue with your outside unit
Refrigerated air conditioning involves a heat exchange. The cool air created in this exchange is distributed through your home, and the warm air is pushed out. Your outside unit is responsible for dispersing the warm air. But if the unit is having issues, the heat gets sent back inside!
Before we get to issues requiring professional help, here’s a DIY solution:
- Inspect your outside unit.
- Remove any leaves, twigs, dirt, or debris from the surface and sides of the unit.
- Gently spray the outside unit fins with water to remove any dirt. If the unit is extremely dirty, get a professional to maintain it.
- Make sure the unit has at least 2 feet of breathing room on all sides. Clear away any weeds and plant growth within 2 feet.
- Head back inside to see if your AC is blowing cold air.
Debris buildup on the outside unit limits airflow (and the cotton fluff we have in New Mexico is especially bad!) The unit should be cleaned once a year. We suggest getting a professional to do routine maintenance and cleaning every spring.
Don’t want to mess with your AC? Pass the mess to us!
So, what happens if you cleaned your outdoor unit, and it’s still blowing hot air inside? There are two more possibilities for outside unit issues:
Your compressor needs to be replaced.
The compressor is the device inside the outdoor unit that pumps refrigerant through the system. If the compressor is old or damaged, the refrigerant doesn’t circulate properly. The AC loses cooling capacity and blows warm or hot air. Unfortunately, the only way to fix it is to replace it.
Pro Tip: Compressors are expensive. Before purchasing one, check your AC parts warranty (both with the manufacturer and the contractor who installed it). If the warranty has expired or doesn’t cover the compressor, consult an HVAC professional. It’s probably more cost-effective to replace the whole air conditioning system, depending on the age of the unit.
The refrigerant metering device is jammed.
If “refrigerant metering device” sounds technical, don’t worry. It’s like a valve that controls how much refrigerant goes into the evaporator coil. You might have heard it called a TXV or capillary tube. If it gets jammed, refrigerant doesn’t circulate properly through the system. It can be fixed, but for this one, hire a professional instead of trying to DIY.
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If everything’s great with your outdoor unit, the refrigerant is the next thing to check. Let’s take a look.
3. Your air conditioning system has a refrigerant leak
Refrigerant is the lifeblood of your AC. It’s the heat-transfer chemical responsible for cooling the air inside your home. If there’s a refrigerant leak, your air conditioner loses the ability to absorb heat. Over time, less and less refrigerant is available in the system, causing the air to get warmer and warmer.
How to tell if you have a refrigerant leak:
- You hear a hissing noise coming from your AC system
- There is ice on the AC refrigerant lines, and/or the evaporator coil is frozen
- There is water pooling around your air handler (indoor AC unit, probably near your furnace)
- You experience higher-than-normal energy bills
Sadly, there’s no DIY option for a refrigerant leak. You’ll need a professional to find and repair the leak before recharging the system with fresh refrigerant.
Think you have a refrigerant leak?
Quick heads up: If you have an old AC, it might need a refrigerant type (like R22) that’s no longer available due to environmental regulations. In some cases, it makes more sense to replace the air conditioner rather than pay a lot of money to recharge an old one. Your HVAC tech will help you explore options and come to the best decision for your family.
Okay, we’ve covered a lot of information. We’ve looked at thermostat settings, the outdoor unit, and refrigerant. If all of these are fine, there’s one more thing to check: the evaporative coil.
4. Your evaporator coil is dirty
The evaporator coil is where the heat exchange takes place. The coil sits just inside the indoor air handler and is made up of many copper coils, each filled with refrigerant. The coil’s job is to absorb heat and moisture from the air, creating cool air that’s distributed through your home via air ducts and vents.
If the evaporator coil is dirty, the dirt acts as a barrier between the warm air and the cold refrigerant. It stunts the heat exchange process, keeping the refrigerant from absorbing enough heat. The air stays warm but still gets distributed through the house. It’s very uncool (see what we did there?)
Pro Tip: A dirty evaporator coil needs professional attention right away! Because it prevents the heat exchange from taking place, the cold from the refrigerant has nowhere to go. The coil eventually freezes into a solid block of ice. It’s not a cheap or easy repair, so it’s best to avoid it by regularly changing your air filter (every 1-3 months) and getting your AC annually maintained.
So, what should you do if you have a dirty or frozen evaporator coil? There’s only one thing to do. Call TLC!
Need emergency AC service?
We’ve covered the four main reasons your AC is blowing hot air. Of course, there are other possibilities, but these are the most common. And some of the solutions are DIY friendly, which is always a plus!
If you need help or don’t have time to mess with it yourself, no sweat. Our HVAC techs handle problems like these every day! Just give us a call at 505-761-9644, or request an appointment online.