If your air conditioning unit isn’t blowing cold air, it’s possible the compressor in your condenser failed or you have a refrigerant leak. An HVAC technician should be the one to handle either issue.
However, the issue may be as small as a dirty air filter. It’s hard to say. Diagnosing the issue properly compels you to understand how your central A/C cools your home. How does the refrigeration cycle work? What equipment and components have a hand in the process?
Table of Contents
- A Quick Overview Of The Refrigerant Cycle
- Possible Reasons Why You’re Not Getting Cool Air
- Related Questions
A Quick Overview Of The Refrigerant Cycle
First, let’s look at the equipment installed in your home. You have central A/C. That means you have four major components:
- An evaporator coil.
- A condenser.
- A compressor. (This actually sits inside the condenser. More on that below.)
- A pair of refrigerant lines: one carries vapor, while the other carries liquid.
Each piece of equipment has at least one component which, if fails, would cause your system to blow air at your home’s current temperature. Here’s how they all work together:
- It’s 85 degrees Fahrenheit outside. You set your thermostat to 72°F, which closes a circuit to both the compressor and condenser fan motor. Once these units turn on, the refrigeration cycle begins.
- The compressor takes superheated vapor refrigerant coming from the evaporator coil and turns it into a high pressure, high temperature vapor.
- The high pressure, high temperature vapor then moves through the condenser, which allows the refrigerant to expel the heat it’s accumulated in the evaporator coil.
- In the middle of the condenser, the refrigerant transforms into a saturated state. A “saturated” state is one in which liquid and vapor refrigerant exists simultaneously.
- Once the condenser removes heat from the saturated refrigerant, it turns into a sub-cooled liquid. The sub-cooled liquid enters the liquid line as a high-pressure, low temperature refrigerant.
- Before the high-pressure, low-temp refrigerant enters the evaporator coil, a metering device drops the refrigerant’s pressure, further lowering its temperature.
- The refrigerant enters the evaporator coil as an 80-percent liquid, 20-percent flash-gas mix.
- A blower pushes warm air from your home over the evaporator coil, cooling the air before delivering it to registers located throughout the house. The warm air is your “return” air, and the cool air is the “supply.”
- As warm air passes over the evaporator coil, the refrigerant begins to absorb the heat contained in the return air. The refrigerant turns into a saturated state again, before turning into a superheated vapor.
- The superheated vapor then enters the compressor, completing the cycle once again.
Keep in mind what each part of the system is designed to do: The compressor turns the superheated refrigerant vapor into a high-pressure, high-temperature vapor. The condenser allows the refrigerant to reject heat, saturate, and then turn into a cool liquid. The metering device turns that liquid into a liquid/vapor mixture.
Possible Reasons Why You’re Not Getting Cool Air
First, let’s assess the state of the evaporator coil. From there, we’ll move to the compressor, condenser, and other components in the system.
Reason No. 1: Poor Air Flow
Go to the unit installed in your home. It should be in your attic or basement. You’ll see the return ducts entering the bottom of the unit (if it’s standing vertically) or the left-hand side (if it’s lying on its side). Just after the return duct should be a slot for an air filter. Pull out the air filter.
Just as a test, run the A/C again. Wait about 15-20 minutes. If the air starts to get cool, you know poor air flow was the problem. Open up the jacket of the unit itself and take a look at the evaporator coil. If the coil’s starting to defrost (it should be covered with ice), then you know you’ve solved the problem.
Lesson learned: replace your dirty air filter. If you have pets in the house, you’ll have to do this quite frequently.
Reason No. 2: Bad Thermal Expansion Valve
Remember the metering device discussed earlier? That’s the thermal expansion valve (TXV). Its job is to limit the amount of liquid refrigerant entering the coil. In the process of doing so, a portion of that liquid turns into a vapor.
This is where we’d recommend consulting a technician. Diagnosing a TXV can be complex and, at times, misleading. A licensed technician has the tools and know-how to determine whether the TXV is the culprit. He or she will look at readings such as:
- The evaporator suction pressure.
- The evaporator and compressor superheats.
- How many amps the compressor is drawing.
- Whether the low-pressure control keeps short cycling.
Reason No. 3: Refrigerant Leak
This is one of the most likely culprits behind your problem. If there’s not enough refrigerant moving through your system, it doesn’t have the capacity to the cool the air circulating throughout your home.
A refrigerant leak is detrimental to both you and your loved ones’ health. According to Medical News Today, it can lead to mild refrigerant poisoning, so it’s best to address the issue as soon as possible.
Upon calling a technician to your home, he or she will test the pressures of the refrigerant within your system. If anything seems glaringly off (one of them being a very low suction-side pressure), he or she will take the following steps:
- Recover the existing refrigerant from the system. This is mandatory per Environmental Protection Agency regulations. In fact, every HVAC technician should have an EPA Universal certification. Make sure yours has one!
- Put the system on a nitrogen test to determine where the leak exists. If the leak exists at the condenser or the coil, the technician may advise replacing either unit. Some would recommend replacing both the coil and the condenser, depending on the age of your system.
- If a leak is found somewhere in the refrigerant lines, the technician will recommend replacing them altogether.
- Once the technician has identified and corrected the leak, he or she will put the refrigerant lines under a nitrogen pressure test again. If no further issues are found, he or she will put the system on a vacuum to remove any air or moisture.
- After the vacuum cycle ends, the technician will add new refrigerant to the system.
Reason No. 4: Bad Compressor
When the compressor fails, it can no longer turn the superheated vapor into a high-pressure, high-temperature gas. That means the refrigerant can no longer expel the heat it accumulated in the evaporator coil.
If a technician identifies a bad compressor as the culprit, think about the age of your system. If it’s over 12 years old, most technicians would recommend replacing the condenser and compressor altogether (they’re sold together). At that point, replacing the condenser wouldn’t prolong the life of the system too much.
Reason No. 5: Your Condenser’s Covered With Debris
It is possible that your condenser is simply covered with debris. If that’s the case, you know what’s wrong: the refrigerant has nowhere to expel the heat. It needs a free atmosphere. Clean it off, then test the system again. It’s likely you won’t have to call out a technician for this.
This depth of this issue can be both complex and simple, depending on what’s failing. Start with the basics, and then consult a technician based on what you find. If a dirty air filter’s all that’s preventing you from keeping cool, that’s an easy, cheap fix.
Why Does It Take So Long To Cool My Home?
It’s possible your A/C system’s undersized. If it’s a problem you’ve always had, then you should think about upsizing the coil and condenser. Hire a technician familiar with fully-ducted installations. He or she will take into account:
- The dimensions of each room.
- The types of windows installed in your home, as well as their orientation toward the sun.
- The insulation throughout your home. Does the attic have a proper thermal resistance? Do you have batt, spray-foam or loose-fill insulation?
- The appliances in your home that throw off heat.
- The number of occupants currently living in your home.
On the other hand, you may just have to turn the thermostat down. If you live with others, some may like it warmer than you do.
Why Isn’t My Air Condenser Running?
First, check to confirm that the blower motor below your evaporator coil is running. If so, then the unit may not be receiving power. On the other hand, the motor may have failed.
Before calling in a technician, go outside to the condenser itself. There should be what’s called a “disconnect” – a grey metal box – with a pull-out switch. Removing this switch kills power to the condenser.
From there, you can remove the cover to the unit and take a look at the wiring. Anything chewed or frayed? Any burn marks? Look for these symptoms and report them to the technician. Take pictures. He or she may be able to spot an issue the untrained eye cannot.