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Why Is My AC Leaking Water? A Tucson Tech Explains

First things first: If your inside AC unit is leaking water in your Tucson home, shut off your thermostat ASAP to prevent further water damage.

Once you turn off your AC, you’ll need to determine why your system is leaking water, and what you need to do to fix it.

There are a variety of reasons why your AC could be leaking, but some of the most common include:

  • A clogged air filter
  • A leaky drain pan
  • A clogged condensate drain line
  • A low refrigerant level

Below, we’ll first look at why (and how) your indoor AC unit forms water in the first place. Then we’ll explain how the above issues can cause your AC to leak, and more importantly, what you can do to fix it.

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Why and how water forms in your AC’s indoor unit

If you’ve noticed that your AC is leaking water in your home, your first question is probably: “Why do AC units have water inside of them anyway?”

To explain, let’s look at how your AC system cools your home. First, your AC pulls in warm air from your home and blows that air over a cold evaporator coil.

The warmth from that air is absorbed by cold refrigerant lines that run through the evaporator coil. After the heat is absorbed, the refrigerant carries the heat outside and dumps it, leaving cool air for your AC system to blow back into your home.

During this process, water naturally forms when warm air comes into contact with the cold evaporator coil. The moisture inside of the air condenses on the coil, causing water droplets to form.

Eventually, this condensation drips off the coil and into a drain pan. This condensation then exits your home via a condensate drain line.

However, if you have one of the issues we listed in the blog’s introduction, you will notice water puddling around your AC unit.

Below, let’s review each of the issues and their corresponding fixes.

AC Leak Reason #1: A clogged air filter

How does a clogged air filter cause your AC to leak, you ask?

Well, your AC filter is responsible for preventing dust and debris from entering your AC system. Over time, this filter catches so many particles that it clogs up, which makes it difficult for your AC system to pull in enough warm air to cool your home.

If the airflow coming into your AC decreases, there won’t be enough warm air blowing over the evaporator coil. Since the coil is full of cold refrigerant, the coil will then freeze and ice over. Once the ice starts to melt, the water can easily overflow the drain pan, which may be why you see a puddle around the base of your AC.

  1. Turn off your AC system. Easy to forget, but don't skip this step.
  2. Check your air filter: If it looks like the filter on the right, it’s time to replace it. Note: On average, you should replace your air filter every other month, except in the summer when you should replace it monthly.
  3. Turn your AC back on: Once you have replaced your filter and the ice on the coil has melted, turn your AC back on. If the leakage stops, problem solved. If you still notice liquid around your AC, keep reading.

AC Leak Reason #2: A leaky drain pan

As we mentioned above, the drain pan catches all the moisture dripping from the evaporator coil. Because the drain pan is constantly filled with water, it has a tendency to rust and crack, which allows water to leak everywhere.

Your AC system actually has two drain pans. One pan is permanently attached to the evaporator coil; the other pan is removable and is located underneath your AC unit.

To fix your leaky drain pan, start by turning off your AC unit and inspect your drain pans with a flashlight.

If the removable drain pan underneath the AC unit is cracked, you can use a water sealant to fill in the cracks. However, the water sealant is a temporary fix, so you’ll want to get a replacement drain pan ASAP to prevent further water damage.

You can buy a replacement removable drain pan at home improvement stores, such as Home Depot or Lowe’s. To ensure you buy the right drain pan, jot down the model number listed on your AC’s manufacturer sticker and ask a store attendant to help you find the right drain pan for your AC.

However, if the permanent drain pan has cracks, you’ll need to call a professional to replace the drain pan. If you try to replace this drain pan on your own, you may end up causing accidental damage to the evaporator coil.

AC Leak Reason #3: A clogged condensate drain line

If your AC is leaking water during Tucson’s monsoon season, a clogged condensate drain line is probably the reason behind the leak.

Monsoon season increases both the amount of moisture and dust in the air. When the extra dust gets in the drain line, water can back up and overflow the drain pan, causing an AC leak.

However, if your AC is leaking and it’s not Monsoon season but you notice your AC has shut off, you could still have a clogged drain line. Most AC systems automatically turn off when they detect a drain line clog. This prevents extra water from leaking from your AC system and causing water damage to your home.

To unclog the drain line:

  • Find the end of the drain line. You’re looking for a narrow PVC pipe attached to the wall next to your outside AC unit.
  • Seal the mouth of a wet/dry vacuum’s hose onto the end of the line.
  • Make sure the suction is tight then turn on the vacuum for about 3 minutes.

If the vacuum doesn’t clear out the drain line, you might be dealing with a major clog or a clog higher up in the drain line. In that case, you want to call a professional to clear out the clog to avoid risking significant damage to your AC system.

AC Leak Reason #4: Low refrigerant levels

Refrigerant is a liquid agent within the evaporator coil. As we discussed in the introduction, refrigerant’s job is to absorb heat from your home and dump it outside.

If refrigerant levels drop, your AC won’t be able to absorb as much heat as it needs to. When this happens, the evaporator coil gets colder and colder, which causes the moisture on the coil to freeze. Once the ice melts, the drain pan leaks water everywhere — much like what happens with a clogged air filter.

Anytime you see water leaking around your AC and/or hear a bubbling or hissing sound from your AC, you most likely have low refrigerant levels.

If your refrigerant levels are low, it means your refrigerant lines are leaking. Refrigerant doesn’t work like your car gas tank — it doesn’t run out. So, if your refrigerant levels are low, it means you have a leak somewhere in your line. You will want to call a professional who can repair the leak and then refill your refrigerant levels.

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