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Common Problems:
Strange Noises Coming From the Air Conditioner
Moisture Leaking From the Air Conditioner
Get in Touch With an Air Conditioning Professional
Air conditioning systems can be pretty complicated, with a ton of important parts all working together. It’s kind of an engineering marvel, but having all those complex systems interacting means that there are a lot of opportunities for something to fail. Between the thermostat, the evaporator and condenser coils, and the various fans and motors that run the whole thing, it can be tough to tell why your air conditioner has stopped working.
However, if you learn a little bit about what can go wrong inside an air conditioner, you can save yourself some headache and even a little money later down the road. Being able to identify problems in your HVAC system makes things easier for the air conditioning repair specialist you call, and you might even be able to fix a few things by yourself. Air conditioners can be finicky beasts, but once you understand what’s going on inside, they become a lot easier to deal with.
That’s why we created this quick and easy troubleshooting guide for some of the most common problems you might run into. Here’s what you need to remember in order to identify the most frequent air conditioning concerns, and maybe even get started on learning to fix them yourself.
Air Conditioner Won’t Turn On
If the A/C won’t turn on altogether, your first thought might be that the whole thing is completely dead or busted. Luckily, that’s not usually the case. Before you write the system off and start looking into buying a new one, there are two things you should look into that could be causing the issue.
Non-Functional Thermostat
If this is the reason why your air conditioner won’t turn on, then you’re actually in pretty good shape because it means the rest of the system is likely perfectly fine. Unless you have a small window box with the controls right there on the unit, your entire air conditioning system is running through the thermostat. Here’s how it works:
Thermostats have two main functions for an HVAC system. First, they have temperature sensors inside that are constantly measuring the temperature inside your house. Second, they check that data against the temperature settings controlled by you, the user. If the temperature is warmer than you want it to be, then the thermostat turns the air conditioner on. If the temperature is perfect or colder than you wanted it, then the thermostat turns the air conditioner off.
Pretty simple and straightforward, but you can probably already see how a problem with the thermostat can cause the system to stop functioning. If the thermostat itself is failing, then the air conditioner isn’t receiving any signals to turn itself on. This could be a problem with the temperature sensor, the computer inside the thermostat, or the connection between the thermostat and the rest of the system. We’ll talk a little more about diagnosing thermostat problems later on in the blog, so keep reading!
Lack of Power Flowing to the System
If your thermostat seems to be working fine but the system still isn’t turning on, then you could have a problem with the power. As you might guess, if there’s no electricity flowing into the air conditioner, it obviously can’t turn on. There are a few reasons why this might be the case, but the first thing you should do is go outside or down to the basement and check on the circuit breakers.
It’s not uncommon for an air conditioner to use a little too much juice now and again and trip a circuit breaker, so you should start by checking on the fuse box. If the circuit that controls the air conditioner has been tripped, then you’ve already solved your problem – just flip it back on and everything should go back to normal. It should be noted, however, that if you keep getting this problem over and over, you should call a professional to come take a look at your air conditioning system. Tripping a circuit once or twice isn’t a big deal, but if it becomes a constant issue, then there’s probably a bigger problem with the unit.
If the circuit hasn’t been tripped but the unit still won’t turn on, then it could be a problem with the wiring or the motor inside. We’d recommend calling a professional repair specialist to take a look at the system in this case, although if you have experience with electrical systems and wiring you should feel free to take a look inside. Just make sure you go to the fuse box and switch off the power to the air conditioner first, just to be safe.
Problems With the Thermostat
If you’re having issues with your thermostat, that can obviously affect the whole system. Here are a few common issues you might run into with your thermostat.
Blank Screen
If the screen is just blank, then there’s a pretty good chance that the thermostat is out of batteries. Luckily, that’s a pretty easy fix. Just check the instruction manual for the thermostat to find out the best way to take it off the wall, change the batteries, and replace it.
If you’ve changed the batteries and the screen is still blank, then you might have a problem with the wiring inside. In this situation, a new thermostat might be required – the cost of bringing someone in to attempt a repair will likely be higher than just buying a new one. However, if you have some knowledge in electrical systems, it’s worth opening up the unit and at least checking for loose or disconnected wires. Thermostats are very delicate on the inside, so it’s easy for something to be jostled loose accidentally.
Thermostat Not Reaching the Set Temperature
If the thermostat is on and functional but isn’t setting the temperature for the room correctly, there are a few problems that might be causing it to fail. The most common issue is a problem with the temperature sensors inside the unit. Unfortunately, there’s not a whole lot you can do in this instance other than just buying a new unit, since repairing a broken sensor is tricky at best and impossible at worst.
If you just installed a new system but the thermostat isn’t working properly, you might just have it in the wrong place. Placing it directly underneath an air vent, for example, can cause the sensors to think the room is colder than it really is, and having the thermostat near the fire can cause the opposite problem. Take a look around to make sure there’s nothing near the unit that might trick the temperature sensors.
On the other hand, if you’ve had the same thermostat for a while, it might just need cleaning. Over a period of years, dust, lint, and other particulates can make their way inside the thermostat and cause problems. To fix this, all you have to do is clean it. We recommend wiping down the outside of the thermostat with a cloth and then cleaning the inside with a soft brush. Be very careful when cleaning the inside of your thermostat, as the wires and sensors inside are pretty delicate.
Strange Noises Coming From the Air Conditioner
It’s normal for air conditioning systems to make some noise, especially large ones. After a little time, you get used to the loud whirring of the motors and the blowers inside the units. However, if you start noticing sounds coming from the air conditioner that you don’t recognize, then you might have a problem. In most cases, you’re probably going to end up calling a repair specialist to take care of whatever is making the noise. That being said, it’s still valuable to at least be able to guess what the problem might be. Different sounds can indicate different issues inside the unit.
High Pitched Squealing Noises
If your air conditioner is making a squealing noise, then the problem is most likely one of two things – the belt or the bearings in the motor for the condenser fan. Which one is the culprit will largely depend on the age of your unit.
If you have an older air conditioning system, then the squealing noise likely indicates that the belt connecting the motor to the blower has slipped. The noise should be pretty recognizable to anyone who’s ever had the A/C belt in their car slip off. Generally, you can tell that the belt is the problem if you’re hearing the squealing both inside and outside the house. If you think this might be the problem, you should turn the unit off immediately and call someone to fix it.
Newer air conditioners don’t use belts, so if you’ve purchased your system more recently and you still hear a squealing noise, the problem is most likely with the bearings in the condenser fan motor. In this instance, you’ll hear a loud squealing or grinding coming from the outside air conditioning unit. Again, unless you’re especially confident in your air conditioner repair skills, we recommend calling a professional to fix the motor for you.
Buzzing Noises
If your air conditioner is buzzing, then there’s most likely a mechanical issue inside the unit. Air conditioners are made up of a bunch of small mechanical parts that all fit together, and if one of those parts breaks, then it can put a strain on the others. That strain creates the buzzing sound you’ll hear inside the unit. There are a couple of parts that most commonly create this problem when they break.
The first thing you should do if you hear a buzzing is go outside and check on the compressor unit. The outside unit stands on little rubber pads called isolation feet. If those feet crack or break, the entire unit will tilt and create a buzzing noise. Luckily, you should be able to buy new isolation feet pretty easily.
If the feet seem fine, then the problem is most likely a broken part inside the unit. Air conditioners are always vibrating as they run, and a loose part sitting against the metal will cause a buzzing sound as the unit vibrates. If this is the case, then you’ll need someone to open the unit up and fix the broken parts for you.
Moisture Leaking From the Air Conditioner
Air conditioners use condensation as an integral part of the air cooling process, so some moisture inside the unit just means it’s working correctly. However, if moisture is leaking or dripping from the air conditioner, then you might have a problem. Here are a few different problems that can lead to water dripping from the unit.
Clogged Drain Line
If your air conditioner is working properly, then any excess moisture inside the unit is collected in a pan and diverted outside through the drain line. If water is dripping inside your house, then the most likely problem is that the drain line has become clogged with dust, dirt, or other debris. This is a fairly common issue for air conditioners, and it’s part of why we recommend regular maintenance of any A/C system. Many modern air conditioners also have automatic shut-off switches that turn the system off if a clogged drain line is detected, so the drain line is something else you can check if your air conditioner isn’t turning on.
Fortunately, a clogged drain line is pretty easy to fix. You can even do it by yourself without any special mechanical knowledge. The best way to unclog a drain line is to just use a wet/dry vac to suck out whatever is clogging the tube. You can also try using something like a plumber’s snake to push the clog out one end. If the wet/dry vac isn’t working, however, you might want to call in a professional to use a special high-powered A/C vacuum to clear the debris.
Mold can also cause your drain line to become clogged, leading to moisture dripping from the unit. The best way to avoid this is with a little DIY maintenance. Every three or four months, you can prevent mold from growing inside the drain line by unscrewing the cap and pouring about six ounces of vinegar into the line itself. The vinegar won’t cause any damage to the tube itself, but it will kill any mold or algae growing inside.
Broken or Cracked Drain Pan
If you have a crack or a hole in the drain pan, then the excess water won’t even get a chance to flow through the drain line. As a general rule, you should replace the drain pan in your air conditioner every 10 years or so. This is also a relatively simple fix, and a replacement pan isn’t especially expensive. It’s worth noting, however, that most air conditioners have two drain pans – a removable one located at the bottom of the unit, and a fixed one directly underneath the evaporator coils. If the fixed one has a crack, you won’t be able to fix it yourself.
Ice Inside the Air Conditioner
Air conditioners work using cold air and condensation, but you shouldn’t see ice forming anywhere inside the unit. If you do see ice, then something is going wrong with the air conditioning system. The first thing you should do is turn the air conditioner off and let it thaw completely. Make sure you don’t try to chip or break the ice off to speed things up – you could end up causing damage to the delicate coils underneath the ice. There are a few things that can cause ice to form inside your A/C unit, but regardless of the base issue, the solution is most likely going to involve calling an air conditioner repair company.
Not Enough Refrigerant
Air conditioners hold chemicals called refrigerants that help cool the air by switching back and forth between liquid and gaseous form. The system will reuse the same refrigerant over and over, cycling it back and forth between the two forms, so there’s normally not a need to refill it – the whole thing is a closed system. However, leaking refrigerant will cause a number of problems inside the air conditioner, including ice on the condenser coils.
Normally, refrigerant running through the condenser coils will cause water to condense on the coils, pulling moisture from the air. That excess moisture then falls and drains out through the drain line. However, if there isn’t enough refrigerant running through the system, that condensation will stick around, eventually turning into ice on the coils. This is most commonly caused by a hole somewhere in the system allowing refrigerant to leak outside.
Unfortunately, a refrigerant leak isn’t really something that you can fix by yourself. HVAC repair professionals are trained on how to identify the leak, patch it, and replace the lost refrigerant. In this scenario, you’re pretty much stuck biting the bullet and bringing in some outside help. Otherwise, you could end up causing real damage to your air conditioner.
Dirty Air Filter
An air conditioner cools the air by sucking it into the unit, passing it over the evaporator coil, and then blowing it out the other side. All modern A/C units are equipped with air filters to make sure that the air blowing into your house is nice and clean. However, if you don’t replace the filters frequently enough, they can become clogged with dirt and stop air from passing through as quickly. When excess air becomes trapped inside the unit, the extra moisture can cause ice to form on the evaporator coil. Luckily, this can be fixed by simply turning off the air conditioner, allowing the ice to melt, and replacing the filter.
When you buy an air filter for your A/C unit, the instructions should tell you when to replace it. Most filters should be replaced once a month or so, though more expensive ones can last for significantly longer. It’s absolutely vital that you keep up with regular maintenance on your A/C filters. Not only can a dirty filter cause ice to build up on the evaporator coil, but it can also cause dirty air to be released into your house, potentially causing health issues for you and your family.
Faulty Wiring
Sometimes a fault in the wiring can cause the condenser coils to keep running after the rest of the air conditioner has been turned off. This can cause ice to form on the coil and will also make a major dent in your electric bill. If you can hear your air conditioner running even after air has stopped blowing from the vents, then you might have a problem with the wiring inside the unit. We recommend calling a professional to figure out what’s going on and fix any issues they find.
Frozen Evaporator Coils Can Shut Down Cooling Power
One of the most overlooked air conditioning issues in 2025 is frozen evaporator coils—a silent culprit that often causes poor cooling or a total system shutdown. When your A/C runs constantly or airflow seems weak, frozen coils could be to blame. This typically happens when there’s restricted airflow, most commonly due to dirty air filters, blocked vents, or malfunctioning fans.
Frozen coils can also result from low refrigerant levels, causing condensation to freeze on the coil surface. You’ll often notice ice buildup around the indoor unit or unusually warm air blowing from the vents. Letting this issue go unresolved can damage your compressor—one of the most expensive components to replace. To avoid that headache, shut off the system immediately and let the coils thaw before calling a technician for a full system check-up.
How Dirty Air Filters Affect Efficiency and Indoor Air Quality
It might sound simple, but a dirty air filter can throw your entire HVAC system out of whack. In fact, by 2025, HVAC professionals have seen a 40% uptick in service calls due to neglected filters. When filters are clogged, your system has to work harder to push air through, which can lead to overheating, poor airflow, frozen coils, and even system failure.
Even worse? Dirty filters can tank your indoor air quality by recirculating dust, pollen, and allergens. If anyone in your home has allergies or respiratory conditions, this can significantly impact their health. Experts recommend changing your A/C filter every 30 to 60 days, especially during peak usage seasons. High-efficiency filters (like HEPA or MERV-13 rated filters) also offer better filtration and longer lifespans than standard fiberglass ones.
Why Annual HVAC Maintenance is a Smart Investment
Sure, it’s easy to forget, but annual HVAC maintenance isn’t just a suggestion—it’s essential. Preventative tune-ups help catch minor issues before they snowball into major repairs. In fact, most HVAC manufacturers now require regular maintenance to keep warranties valid, which is often overlooked by homeowners.
A professional inspection usually includes cleaning coils, checking refrigerant levels, testing electrical connections, inspecting the thermostat, and clearing the condensate drain line. In 2025, smart thermostats now sync with HVAC service alerts, making it easier than ever to stay on top of maintenance schedules. If you’re aiming for energy efficiency, lower utility bills, and longer system life, scheduling that annual checkup is one of the smartest moves you can make.
Get in Touch With an Air Conditioning Professional Today
If you’re having trouble identifying an issue within your air conditioning system, or the problem is something that you can’t fix by yourself, you should look to a local service provider for assistance. Having an air conditioning repair company that you know and trust is an important part of keeping your A/C system running, whether that’s through troubleshooting, repairs, or just standard yearly maintenance. With experienced professional help, you can go back to relaxing and enjoying the cool air without any problems or drains on your electricity bill.
If you’re in Sonoma, Marin, or Napa counties in California, Valley Comfort Heating & Air is here to help you with all your HVAC needs. Whether you’re installing a new system or fixing a problem with your existing one, we have the years of experience you need to know you’ll be well taken care of. You can get in touch with us online, visit our location in Santa Rosa, or give us a call at (707) 539-4533. No matter what your needs are, we’ll make sure to take care of them for you in a timely, professional, and cost-effective fashion.
