Auto A/C Terms - Glossary
Discharge Air

The A/C system is designed to remove the heat from the air that enters the vehicle. In doing that, it provides temperature control and passenger comfort. When diagnosing auto A/C systems, it is common to check the temperature of the discharge air that is exiting the dash vents in the vehicle.

The discharge air temperature will range depending on several factors including the efficiency of the A/C system and the ambient air temperature and relative humdity of the day.

Typically, the discharge air is expected to range around 40 degrees F. However, understand that when ambient air temperatures rise with increased relative humidity in the air, it is not uncommon for the discharge air temperature to increase as high as 50 or 55 degrees F. In some cases, even on a properly working A/C system, some may consider those higher discharge air temperatures as a sign that the A/C system is not working properly. The truth is, there is no hard and fast rule regarding what those discharge air temperatures should be.

The A/C system is only a method of removing heat from the air as it is entering the vehicle. When ambient air temperatures rise, it is common that the discharge air temperature increases because the A/C system is only capable of removing a fixed amount of heat.

Also understand that humidity in the air actually adds heat loads. In fact, on days with very high relative humidity, that humidity can add as much as 5 times the heat load to the A/C system. Those extreme heat loads are reflected in higher discharge air temperatures.