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(707) 539-4533 |  Sonoma Napa and Marin Counties




Like all machines, air conditioners have a ton of little parts that all need to be correctly working together for the system to operate. The complexity of the equipment is what makes AC units so very good at cooling the air in your home effectively and efficiently, but it does mean there are plenty of opportunities for something to go wrong. You’ve probably never heard of air conditioning drain holes before, but if you own an AC system, there’s a decent chance you’ll have to learn about them at some point.


One nice thing about a clogged drain hole is that it’s a problem you can actually fix by yourself, without having to bring in an HVAC technician to do it for you. All you need to do is learn where the holes are, how to tell when there’s a clog, and how to remove the clog so the system can run properly again. Fixing a clogged AC drain hole only takes a few minutes and can save you some money if you handle it yourself. In this post, we’ll talk a little bit about what the drain holes are for and how to fix them if they become clogged.


HVAC 101 Everything you need to know


How Air Conditioners Work


It’s always a good idea to start at the beginning, so it helps to understand how air conditioners actually work before you try to fix problems with them. At their core, AC units manage the temperature through carefully controlled transfers of heat energy. There are three main parts of an air conditioner that make this happen. No matter the size or the type of AC unit, it will always have these same three primary components – a compressor, a condenser coil, and an evaporator coil. These three parts help transfer heat away from the air in your home, cooling it down.


The compressor is kind of like the heart of the air conditioner. It holds the central motor and controls the flow of a special fluid called a refrigerant. The refrigerant flow in air conditioners back and forth between the two coils is the basis for the heat transfer inside the unit. The compressor is also connected to a thermostat, which is how the system knows when to turn on and blow cold air inside. Window AC units have built-in thermostats, while larger split-system ones use an external thermostat somewhere inside the house.


The function of the two coils is to change the refrigerant back and forth between gaseous and liquid form. As the name suggests, the condenser coil holds the refrigerant while it condenses into a liquid, and the evaporator coil holds it when it evaporates back into a vapor. The compressor quickly cycles the refrigerant back and forth between the two coils, allowing the air conditioner to run consistently until the compressor motor is turned off by the thermostat.


The coils themselves are made of thin copper or similar metal, a material that’s easy to conduct heat through. When the cold liquid refrigerant flows into the evaporator coils, it absorbs heat from the air inside your house, and as the now-warm refrigerant gas passes into the condenser coils, it releases that heat, which is vented outside as exhaust. The newly-cooled air from your house is blown right back out into the room or a ventilation system. That makes an air conditioner a closed system – it’s the same air being cycled through the HVAC system over and over, but the heat energy held in the air molecules is constantly being absorbed by the refrigerant and then released out through the exhaust vents.


The chemistry involved in the compressor cycle in air conditioners might bring flashbacks to high school science class, but the whole process is fairly simple if you look at it as a whole. Air conditioners have worked the same way for about a century now, and will continue to do so for the near future at least.


Why are Drain Holes Essential for Air Conditioning Processes Anyway?


At this point, you’re probably wondering when exactly we’re actually going to talk about AC drain holes. Remember that the refrigerant flowing through the coils is very cold when it’s in liquid form. Just like a water bottle left outside in the sun, a coil holding a cold liquid surrounded by warmer air is going to pick up some condensation on the outside. As the AC unit runs, condensation will gradually collect on the coils.


Condensation buildup inside your air conditioner is a problem for a few different reasons. The first is just your regular, everyday water damage. While the metals used to make AC parts are always rust-proof, that doesn’t mean they’re immune to all water damage. Water is a natural solvent, which means it’ll gradually wear down anything it drips or flows onto. A steady accumulation of condensation can cause some wear and tear on the parts inside your air conditioner, creating problems for you down the road. Excess moisture can also promote mold growth, and we probably don’t need to explain why having mold growing right in your air supply isn’t exactly the best idea.


Having moisture built up on your AC coils can also cause ice to form, especially if the refrigerant levels are low and the system overcools. Ice inside the air conditioner will severely decrease the efficiency of the unit, while also causing more serious damage to the delicate fins of the coils themselves. If you notice ice building up in or on your AC unit, you should immediately switch the system off and wait for it to thaw. Don’t try to break off the ice to speed up the process – the coils can easily become bent or broken.


To combat the condensation problem, air conditioners have a few different ways to drain excess water outside the unit. Split-system central air conditioners use a big pan located under the unit to collect all the moisture, which then flows outside through the drain line. Smaller window units also often use a drain pan, but instead of using a thin pipe to drain the extra water, they just have drain holes at the bottom of the unit. Some window air conditioners have something called a slinger ring attached to the blower fan, which picks up water from the drain pan and splashes it against the condenser coils, helping keep the system cool. The slinger ring will sometimes drain the water as well, although these units typically have drain holes just in case.


If the drain holes in your window AC unit become clogged, they’ll allow moisture to build up inside the unit. This can cause problems for the air conditioner, but it’ll also cause some problems for you as well. Having a pool of stagnant water in your window isn’t the best thing in the world, and the water will eventually rise to the level of the intake vents, causing it to spill out into the room. Too much water can also damage the electrical parts of the unit, including the thermostat and the motors in the compressor and the blower fan. Luckily, drain hole maintenance is fairly easy and straightforward to perform.


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How You Should Be Maintaining These Important Parts for Your Air Conditioner


The good news is that, in some ways, drain holes and lines tend to maintain themselves. Since water is constantly flowing through the drains, it’s difficult for clogs to form in the first place. However, drain clogs are still one of the most common maintenance issues we see in residential air conditioners. This is usually caused by dust or other little bits of debris falling into the lines or the holes and blocking them, although sometimes the excess moisture left over inside a drain line can cause mold to start growing, blocking the line from draining properly.


AC maintenance on a clogged drain hole is fairly easy for any homeowner to handle. Generally, the hardest part is actually finding the holes. In older window units, they’ll usually be located on the bottom of the outside part of the unit, fairly visible. In newer units with a drain pan, the drain holes are often closer together, since the pan drains through a single hole in its bottom. If your window AC unit isn’t draining, the first thing you should do is turn it off. Then, try tilting the unit back just a little to see if gravity will help drain any water that’s stuck inside. Make sure you use two people when tilting the air conditioner since they’re pretty heavy and it’s hard to manage one by yourself. If the holes seem clogged or blocked, you can easily clean them out with a pipe cleaner, drain snake, or even a wire hanger. You can also spray the underside of the unit with a hose to dislodge anything stuck underneath.


If you have a split-system air conditioner with a clogged drain line, the best way to clean it is with suction. Turn the system off, use a shop vac to clean any standing water stuck in the drain pan, and then use the vacuum to suck the clog out through the drain’s exit point outside your house. Keep the vacuum running for about a minute, and be sure to check the canister to make sure you actually got the clog. Next, you’ll need to find the access point to the drain line. The port is usually a T-shaped vent with a PVC cover. Pour some distilled vinegar or a peroxide solution down the drain line to clean it, and then flush it with water after about half an hour. Repairing an AC drain line in case of holes is more difficult, but it can be done with a certain amount of plumbing knowledge.


The process of how to clean an AC aerator is fairly similar to the drain line. Vinegar is a great tool to clear out clogs and debris from any kind of drain. Plumbers often use it to clean faucet aerators in areas with hard water that causes mineral buildup and other frequent clogs.


Simple Fixes for Troublesome Drain Holes


It can get a little aggravating having to clean out the drain holes or the hose every so often, but it’s well worth the effort. Allowing water to build up inside the air conditioner will lead to plenty of potential problems down the road, so your best bet is to stay on top of the drain maintenance as much as you can. If you have a window unit, spraying it down with a hose every once in a while is a great way to make sure nothing collects in the drain holes or elsewhere and should only take a couple of minutes. If you do get a clog, a pipe cleaner or snake should do the trick.


Drain lines are a little more complicated, but suction and vinegar should take care of most clogs. If you don’t like the smell of vinegar, you can always try a peroxide solution or even a little bit of dishwashing soap in water. If you have a particularly troublesome clog, or if you’re not sure how to clean the line yourself, you can always bring in some outside help. An HVAC technician can easily clean out even the toughest clogs, as well as make sure everything else inside the air conditioner is running the way it should.


If you’re in Napa, Sonoma, or Marin Counties and you’re having trouble with your drain lines, you can give Valley Comfort Heating & Air a call at (707) 539-4533 or contact us through our website. We’re more than happy to help in any way we can, whether that’s setting up an appointment for a visit from an HVAC technician or just giving you some more in-depth advice over the phone so you can take care of it yourself.


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