What Temperature Should My Central Air Conditioner Be Putting Out?

2017 Jul 07
Posted in: Air Conditioning

Wondering what temperature your A/C should be blowing into your home?

Well, there’s not a universal, fixed temperature your A/C should always be blowing. The temperature your A/C puts out is relative to the temperature you set on your thermostat.

So even though there’s no single ideal temperature, you do want a 15°–18° F difference from the supply air and return air. Professionals call this temperature difference the evaporator Delta T.

When evaporator Delta T is between 15°–18° F, that means your system is working properly. But if temperatures fall outside of that range, it means your A/C has some issues.

In this article, we’ll go into how you can calculate evaporator Delta T and what issues you could have when air temperatures fall outside the ideal range.

Let’s start by going into more detail about evaporator Delta T...

The difference between supply & return air temperature

Just so we’re on the same page, let’s discuss what we mean by supply and return air.


A supply vent register.

Simply put, supply air is the air entering your home through the registers/vents pictured above.


A return air grill.

The air then goes back into your ductwork via the return vent, is cooled, and reenters your home through the supply registers.


Air enters your home through the supply vent, then goes back into the system through the return grill.

The indoor A/C part that actually cools your home’s warm air is called the evaporator coil (pictured as a snowflake in the image above). 

When we calculate evaporator Delta T, we’re trying to see how efficiently the coil is working.

So now that you know supply vs. return air, you can calculate evaporator Delta T:

How to calculate evaporator Delta T

  1. Get a temperature gun with an infrared thermometer
  2. Go to your return vent and record the temperature with your gun
  3. Go to 3 supply vents and record the temperature
  4. Find the average temperature of the 3 supply vents (add the temperatures and divide by 3)
  5. Subtract the return vent temperature from the average supply vent temperature to get Delta T

For more information, watch this helpful YouTube video about calculating Delta T. Of course, you can always have a professional calculate Delta T for you.

“My Delta T doesn’t fit into the 15F°- 18F° range. What does that mean?”

The short answer is, it means something’s not working correctly in your A/C. Let’s look at some common problems:

High Delta T issues (more than 18F° difference)

High evaporator Delta T means that the incoming temperature and outgoing temperature is excessively large. It’s usually caused by low air flow across the coil, which includes problems like:

  • A dirty air filter
  • Fan set to an incorrect speed
  • A dirty evaporator coil
  • An incorrectly sized coil (too small for the air handler)
  • Ductwork is too small

Learn more about why your A/C is blowing hot air.

Solution:

Low Delta T issues (less than 15F° difference)

Low evaporator Delta T means that there’s an excessively small difference between the incoming and outgoing temperature. It’s usually caused by return air bypassing the coil, which points to problems like:

  • Low refrigerant (Freon) levels
  • Weak compressor valves
  • Leaking reverse valves
  • Leaking return air ductwork

Solution:

Hire a professional to check your system for refrigerant leaks and inspect your valves and ductwork.

Is your A/C not blowing at the correct temperature? 

Contact George Brazil to schedule an air conditioning repair. We will send one of our trusted professionals to your home to get your A/C back in tip-top shape.

We’ve been keeping Arizona families cool since 1955.

Related articles