One common customer complaint about their central HVAC systems is that the a/c system is running but not providing any cool air to the controlled space. One of the most common reasons for this situation is that the a/c condenser or evaporator coil has frozen over. This term or phrase literally means that ice has formed on the heat exchanger, preventing the transfer of heat since the ice is acting as an insulator. This article provides an actual case study that illustrates an a/c freeze-up event in a residential unit.

In order to capture various HVAC statistics, a number of monitoring systems were installed in residential central HVAC units in the state of Texas beginning in 2016. A typical HVAC monitoring instrument is illustrated in Figure 1. These units measure and record inlet temperature, outlet temperature, and blower fan current with the following attributes.

In August 2018 the first complete a/c freeze-up event was captured and is summarized in Figure 2.