Should AC Drip Pan Have Water in It? If So, How Much?

Is It Normal for the AC Drip Pan to be Dry?

An AC drip pan, also known as a condensate drain pan is a tray located under the AC’s evaporator coil to catch the condensate as warm and humid indoor air is being cooled.

The question most homeowners struggle with is whether the AC drip pan should have water in it or if it should remain dry. So, what is the ideal situation?

AC drain pan full of water

The primary AC drip pan should have some water in it but it should not be full unless the condensate drain line is clogged. However, it is perfectly normal for the secondary drip pan to be dry (without water), but it could also have water if there is a problem with the primary drip pan.

An air conditioner can have a primary and a secondary drip pan. The primary drip pan is the one that collects the condensate from the evaporator coil and it is therefore expected to have water in it. Secondary drip pans are a backup to the primary drip pans and can be dry or have water in them.

It is not normal for a primary AC drip pan to be dry. However, it is perfectly normal for a secondary drip pan to be dry since it is only serves as a backup to the primary drain pan.

A primary drip pan is supposed to have water in it, as long as it is flowing out through the condensate drain line. However, if the drip pan is full of water, the AC drain is most likely clogged and the system will turn the AC off to prevent the pan from overflowing.

So, how much water should be in the AC drip pan?

The amount of water in the AC drip pan should be up to the point where the condensate drain line is connected. Water level in the pan should not surpass the drain line’s output unless the drain line is clogged and hence can’t drain the water out.

If your air conditioner drip pan is full of water, the condensate drain line is clearly clogged. That causes the water level in the pan to rise and if you have an AC float switch it will turn off the AC to prevent it from producing more condensate to prevent the pan from overflowing causing water damage.

How an Air Conditioner Drip Pan Works

To understand how an AC drip pan works and why you need it in the first place, I believe it is even more important to understand how your air conditioner works.

You see, your AC has an inside unit (evaporator coil) and outside unit (the condenser unit). Heat is absorbed from the indoor air by a refrigerant inside the evaporator coil and released outside by the same refrigerant inside the condenser coil.

The refrigerant enters the evaporator coil as a very cold liquid (about 32 degrees) which also makes the surface of the coil quite cold. The evaporator coil fan pulls warm and humid air from the house through the return air ducts.

When the air comes into contact with coil, the refrigerant absorbs heat from the air and that is how indoor air is cooled. It is then forced out and inside the house though the supply air ducts.

The water vapor in the indoor air (humidity) upon contact with cold coils condenses (turns to its liquid state, known as water). An AC can produce anywhere between 5 and 20 gallons of condensate in a day.

And that is where an AC drip pan comes in. Without it, all that water will drip on the floor or ceiling resulting in extensive water damage.

The AC drip pan is installed under the evaporator coil to catch the condensate. The condensate should however not stay in the pan for long. It should be removed to the outside or into your drainage system.

A drainpipe is therefore connected from the AC drip pan’s side to remove the water from the pan to the outside of your house.

Therefore, an AC drip pan will always have some water in it but as soon as it reaches a certain level it will be removed by the condensate drain line.

Primary vs Secondary AC Drain Pans

There are 2 types of HVAC units:

  • Vertical units
  • Horizontal units

In vertical units, the evaporator coil is located at the top of the furnace or air handler. With these units therefore, the condensate can only flow downwards, thanks to gravity.

For that reason, vertical HVAC units will only have one condensate drain pan located under the evaporator coil.

In horizontal units, the evaporator coil and the furnace or air handler are installed side by side. These installations are common in attics or crawlspaces where there is no enough space for vertical installations.

Because of how these units are installed, there is usually no guarantee that the condensate will flow down in a straight line from the evaporator coil. There is always the potential to flow sideways, outside the coverage of the drip pan.

For that reason, horizontal AC drip pans have a primary drip pan under the evaporator coil and secondary drip pan which spans the entire length and width of the unit.

Since the secondary AC drip pan is a backup of the primary drip pan, it can be dry or have water in it depending on the condition of the primary drain pan.

Unlike primary drip pans which are covered and therefore not visible unless you remove a panel, secondary drip pans are clearly visible and that is why you will notice if they have water in them or if they are dry.

Note: While not likely, it is not unusual for vertical HVAC units to have secondary drip pans. However, secondary drip pans are a requirement for all horizontal units.

What Causes AC Drip Pan to Fill with Water?

As I have already mentioned, An AC drip pan that is full of water is usually a sign of a clogged condensate drain line. When the drain line is clogged, water in the pan cannot be drained out causing the pan to fill with water.

The area around the evaporator coil and inside the AC drain line is always humid which makes it a perfect breeding ground for algae, mold, mildew and other such organism. Failing to clean the AC drain line will cause these organisms to rapidly multiply and completely clog the drain line.

Although your HVAC unit will have an air filter, some dirt particles will still manage to pass through and get trapped inside the drain line. Failing to change the air filter or even using the wrong size or a poor quality filter will make it even worse.

Luckily, air conditioners are designed in such a way that if the drain pan is full of water, the AC will turn off, preventing more condensate from being formed.

A small device known as an AC float switch breaks the flow of electric current to the AC when the water level in the pan rises above a certain point. With the AC off, the refrigerant will not be circulated and warm air from the house will not be pulled by the coil fan.

As such, there will be no more condensate being formed. That is how the float switch prevents the drip pan from overflowing, causing water damage in the house.

A float switch will be located inside the secondary drip pan or drain line if you only have a primary drip pan. If your system does not have a float switch make sure that you install one.

How to Clean an AC Drain Line

To make sure that your condensate drain line stays clear and that it drains the condensate from the drip pan without fail, you need to make sure that you clean it regularly.

Cleaning an AC drain line is as easy as outlined in the steps below:

  • Turn off the air conditioner at the thermostat and electric panel to avoid the risk of electrical shock
  • Locate the drain line access tee vent. It is a small T-shaped pipe with a cap at the top, located very close to the air handler.
  • Remove the cap on the tee. Use only your hands.
  • Pour 1 cup of distilled white vinegar down the drain.
  • Wait for 30 minutes then flush the line with water.
  • Turn the air conditioner back on.
  • Repeat after 1 month

The vinegar will kill all the algae and mold inside the drain line, preventing it from multiplying and clogging the line.

Another method you can use to clean the AC drain line is by sucking the gunk out using a shop vac.

  • Locate the AC drain outside the house.
  • Connect the shop vac’s hose to the drain line using rags or duct tape to form a tight seal.
  • Start the shop vac and let it run for a minute or two.
  • While the shop vac is running, pour some water down the drain tee (inside the house). As the water is sucked by the vac, it will take with it any gunk inside the drain line.
  • Clean the shop van and repeat the procedure regularly.

And basically that is how to easily clean your drain line and keep your AC drip pan from filling with water.

Wrap Up

I hope that by now you know whether you have a primary and secondary drip pan or just a primary pan and which should have water and how much water a drip pan is supposed to have.

I also hope that you enjoyed reading this post and that it was helpful.