Why Is My Air Conditioner Not Working? 10 Possible Reasons

Even the best air conditioners can have issues. Waiting in a sweltering house during a hot Portland summer for a professional to come and fix your AC isn’t anyone’s ideal option. Fortunately, our troubleshooting guide can help you know how to identify some common air conditioner issues that can get your AC back up and running. There is a difference between your AC not working and not cooling, and we help you sort the two with the goal of getting your AC pumping out sweet, cool air quickly.

Why Is My Air Conditioner Not Cooling the House?

Uneven temperatures throughout your Portland home are not uncommon, especially if it is an older home. But if you have been noticing significantly different temperatures in rooms or higher energy bills, there are a few common causes and some easy solutions. 

1. Your Thermostat is Not Set Properly

One of the simplest things to do is check your thermostat setting. In Portland, where summer temperatures can be unpredictable, it’s vital to double-check thermostat settings before assuming your AC is broken. Check to make sure it is not set to heat or that the temperature isn’t set too high.  

If you are still struggling with inconsistent temperatures even when your settings look right, a smart thermostat can make it easier to manage your home’s cooling more precisely. 

Learn whether a smart thermostat is worth the upgrade for your home.

2. Your Air Filter is Dirty

A dirty air filter can impede the flow of air and can cause a host of problems. With Portland’s mix of pollen in the spring and wildfire smoke in the summer, keeping your air filter clean is especially important. According to ENERGY STAR, a dirty filter slows down airflow and forces your system to work harder to keep you cool, wasting energy and shortening equipment life.

Blocked filters cause higher energy bills and can even cause your HVAC system to stop working altogether. Regularly cleaning or changing your air filter will help you avoid a future problem or you can save money and stress with routine maintenance.  

3. Blocked Vents or Leaking Ductwork 

Blocked supply vents can be another reason why your AC unit isn’t putting out enough cold air. Check your vents to make sure there isn’t dirt or dust buildup preventing airflow. Toys, furniture, or closed dampers may also be the problem. Rearrange furniture away from registers and check for obstructions that may have fallen into your ducts by accident. 

In older Portland homes, leaking or poorly sealed ductwork is another surprisingly common cause of uneven cooling and higher energy bills. When conditioned air escapes into attics, crawlspaces, or wall cavities before it reaches your living areas, your system has to work much harder to compensate. If some rooms are consistently warmer than others and vent adjustments haven’t helped, leaky ducts may be the reason.

4. Blocked Outdoor AC Unit

Portland’s rain creates lush greenery that can contribute to debris buildup around your AC’s outdoor unit, so regular maintenance is key. Check for debris around the outdoor unit, like leaves, dirt, or branches, that could be blocking airflow.

5. Ice on the AC Coils

If you see ice forming on your evaporator coils, the system could be freezing up due to low refrigerant or poor airflow. Turn off the unit and check for blockages. If you suspect a refrigerant leak, call a Jacobs HVAC professional. 

It’s important to note that a technician cannot diagnose the issue if the unit is frozen. It must fully thaw before we can proceed with any work, which often takes a day.

A note on refrigerant leaks: Refrigerant does not simply evaporate out of a properly functioning system. If your system is low, there is a leak somewhere. Only EPA-certified technicians can legally handle refrigerant, and the EPA notes that refrigerant exposure can pose toxicity and other health risks if not handled correctly. Do not attempt to “top off” refrigerant yourself. Turn off the system and give us a call.

6. AC Unit Is Undersized for Your Home

If your system runs constantly but never quite gets your home to a comfortable temperature (especially on the hottest summer days),  the problem may not be a malfunction at all. It may be that the unit is simply too small for the space it is trying to cool.

This comes up often in older Portland homes that have had additions built over the years, or in homes where the original system was not sized correctly to begin with. An undersized AC has to work at full capacity all the time, which drives up energy bills and wears the system out faster.

Why Is My Air Conditioning Fan Not Working?

If the fan on your AC unit stops working, it could be something as simple as your circuit breaker tripping or something more complex. 

7. Burnt Out Condenser Fan Motor

An air conditioning fan motor is a fairly uncomplicated part, but if it doesn’t work, then your home isn’t going to be cool. Because the fan works hard, it gets a lot of wear and tear, which can lead to a burned-out motor. Intermittently running fans, slow-turning fan blades, or a fan that won’t turn can be a sign the motor has an issue. This is a time when you will need to call an HVAC technician. You can prevent AC fan motor burnouts by regular maintenance and reducing dirt and dust in and around your system. 

8. Capacitor is Failing

No, the capacitor isn’t a time-traveling device. Start-and-run capacitors are devices that send energy to the fan motor and power the air conditioning unit when energy is needed. These small but mighty workhorses keep your Portland home HVAC system working properly so that your AC unit doesn’t come to a grinding halt. When the start capacitor fails, you may hear a humming from your AC without it actually starting up. If your system is short-cycling, randomly shutting off, or delaying AC startup, it may be that your run capacitor is failing. Either way, this is not something you can fix yourself. Call an HVAC technician for help.

9. Condensate Pump is Failing

Checking the condensate pump is a fairly easy DIY test. Condensate pumps typically have shorter lifespans, as they run for both cooling and heating (depending on furnace efficiency). These pumps usually have a test button. Make sure there is some water in the basin, and press the test button to ensure it pumps the water out. A failing or failed condensate pump will often trip the AC so that it won’t run and create a pool of water wherever the AC is (e.g. in the basement or, worse, the attic).

Why Is My Air Conditioner Not Turning Off?

Your air conditioner not turning off is also a sign of a problem. If your air conditioner is constantly blowing, it puts a huge amount of stress on your system, leading to high energy bills and a shorter life span. Beyond checking that your thermostat is at a realistic temperature, a couple of other things could be the cause. 

10. Dirty or Frozen Coils

As covered above in the ice-on-coils section, a frozen evaporator coil can be the reason your AC runs endlessly. Because the system cannot reach your target temperature, it keeps trying indefinitely. Turn it off, let it thaw completely, and check your air filter first. If the problem comes back, there is likely a refrigerant issue that needs professional attention.

A dirty condenser coil has a similar effect from the other direction. The condenser coil’s job is to disperse heat outside your home. If dirt has built up on it, heat gets trapped inside the air conditioner and your system will keep running trying to reach the cooling temperature your thermostat is calling for.

Why Is My Air Conditioner Making Noise?

Air conditioners, when they are functioning optimally, are pretty quiet. The occasional click at the end of a cycle is normal. But if your system starts making persistent or unfamiliar sounds, that is your AC telling you something is wrong. Turn it off and take note of what you heard since the type of sound is often a clue to the cause.

• Rattling or banging usually means something has come loose, like a screw, panel, or component vibrating against the housing as the unit runs. Banging tends to be louder and more serious, often pointing to a broken part inside the compressor or a fan blade that has come free. Check the outdoor unit for debris like sticks or leaves that may have gotten inside. If the noise is coming from within the unit itself, do not run the system.
• Buzzing or humming almost always points to an electrical issue, like a failing contactor, loose wiring, or a problem with the capacitor. A low hum without the system starting up is often a sign the capacitor is going. Do not keep resetting the system hoping it will clear up on its own.
• Hissing typically signals a refrigerant leak, gas escaping through a small break in the line. 
• Squealing or screeching usually comes from the fan motor or blower, often due to worn bearings. 

Any persistent noise is a sign something needs attention. Turn off your AC and contact a Jacobs technician to assess your system.

Can I Reset My AC?

Most professionally installed ACs will not have reset buttons, but they will have a circuit breaker. If you have an older Portland home in areas like Sellwood-Moreland or the Alberta Arts District, you may have outdated breakers that have a hard time handling your HVAC system. Check your breaker box and, if needed, upgrade. 

Power outages or surges, while rare in Portland, can be the reason your air conditioner isn’t working. However, your system will typically come back on as long as you have power.  After a power outage, it’s a good idea to check your system and your breaker box. Try turning your AC off at the thermostat and resetting your circuit breaker. Wait half an hour before turning it back on. If you are still having difficulties, it’s time to call in a Jacobs professional before the problem gets worse. 

Frequently Asked Questions About AC Problems

Why is my AC running but not cooling my house?

The most common reasons are a dirty air filter, low refrigerant, frozen evaporator coils, or a blocked outdoor unit. Start by checking your filter and thermostat settings. If those look fine, give us a call and one of our technicians can usually diagnose the issue quickly.

How do I know if my AC has a refrigerant leak?

Signs include ice forming on the coils, warm air blowing from the vents even when the system is running, or your AC running constantly without reaching your target temperature. Refrigerant leaks require a licensed professional. Only EPA-certified technicians can legally handle refrigerant, and attempting a DIY fix can cause further damage to your system.

How often should I change my AC air filter?

At a minimum, check your filter every month and change it at least every three months. If you have pets, live near wildfire smoke zones (common in the Portland area during summer), or have allergies, more frequent changes are a good idea. To learn more, check out our guide to how often to change your air filter. 

Why does my AC keep tripping the breaker?

This usually points to an electrical issue, such as a failing capacitor, a motor drawing too much power, or a short somewhere in the system. Reset the breaker once and see if it holds. If it trips again, do not keep resetting it. Call a technician as repeated resets can cause damage.

Is it okay to run my AC if I see ice on it?

No. If you see ice on your evaporator coils or refrigerant lines, turn the system off and let it fully thaw. Running it while frozen can damage the compressor, which is one of the most expensive components to replace. Once thawed, check your filter first. If the problem returns, there is likely a refrigerant or airflow issue that needs professional attention.

What should I do if my AC makes a loud banging or hissing noise?

Turn it off right away. Banging could mean a loose or broken component inside the unit. Hissing often points to a refrigerant leak. Both situations call for a professional inspection before you run the system again.

How long should an AC unit last in Portland?

Most well-maintained central air conditioners last 12 to 15 years. Portland’s relatively mild climate means your system does not work as hard as it might in hotter regions, but routine maintenance still makes a significant difference in lifespan. 

Can a dirty air filter cause my AC to stop working entirely?

Yes. A severely clogged filter can restrict airflow to the point where the evaporator coil freezes over, which trips a safety shutoff and stops the system. It can also cause your system to overheat over time. ENERGY STAR recommends checking your filter monthly and replacing it at least every three months.

Do I need to do anything special to my AC after a Portland summer?

A fall tune-up is a good idea even if your system seemed to run fine. A technician can catch small issues before they become bigger problems. Our maintenance agreements make it easy to stay ahead of breakdowns without thinking about it.