HVAC

HVAC Basics - The Delta T

Name: HVAC Basics - The Delta T
Uploaded: 2025-05-29T13:56:03Z
Duration: 1 min 28 s
Description: This video covers how to check if your HVAC system is cooling properly by measuring the temperature difference—also known as delta T. Learn why a 15–20° difference between return and supply air is key, what could cause deviations, and when it's time to dig deeper into potential issues like refrigerant charge or airflow restrictions.

This video covers how to check if your HVAC system is cooling properly by measuring the temperature difference—also known as delta T. Learn why a 15–20° difference between return and supply air is key, what could cause deviations, and when it's time to dig deeper into potential issues like refrigerant charge or airflow restrictions.

Thermostat

Hard Skills

Troubleshooting

Mark Cukro

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Transcript

So with this system, everything is working. We took the fan and we moved it from auto to on. The fan came on, we turned it to ac. Cool. The AC system and the outdoor unit came on. So far so good. We put it in heat mode. It took a time delay, then the heat came on. Now we're back in cool mode, and I wanna make sure that the air coming out of the vents is enough and that it's at a low enough temperature, which is called the difference in temperature.

This is very important to understand with HVAC. A properly operating AC system should have a 15 to 20 degree delta T, which means difference in temperature. So if the air going in is a hundred degrees, the coldest the air could ever be coming out is 80 degrees. If the air going in is 80 degrees, the coldest it should be is 60 degrees, probably more likely around 65, 66, 67.

So if the temperatures are too low, but everything's working, it could be. That the system needs to be cleaned. It could be that there's a low refrigerant charge, the refrigerant is too high, one of the fan speeds is not working. Something is causing that to happen that we'll have to figure out, and that will be in a different video.

The difference in temperature should be 15 to 20 degrees, so. Okay. Right here, it's 71 degrees. It says 70 on the thermostat. Perfect. One degree plus or minus. Not a big issue. Not all thermostats will match exactly, but we're looking for the difference in temperature, not comparing the actual temperatures.