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[EA37TS]

I recently (last fall) entered into an annual service agreement with an HVAC company for my residence and rental property systems.

After this thread got started I went to my file cabinet and pulled the agreements and supporting documents and included in the packet is a document labeled "Before requesting service"

In the section sub titled "System running" The first two items are:
1. Check for dirty filters
2. Measure the "temperature split" if possible

Item 2 goes on to explain how to measure the split and states that if the temperature split is 14 - 20 degrees no service is required. It also states that if the temperature split is greater than 20 degrees to look for obstructed or closed registers downstream from the air return. They also state that a temperature split less than 14 degrees is an indication of low refrigerant or obstructed or dirty evaporator coils or fins and they should be called for service.

They do provide a caution stating that "point and shoot thermometers" are not adequate for measuring the temperature spilt. They recommend a "clip on style probe style thermometer" with the probe in the registers for 3 - 5 minutes before recording the readings.

They also recommend things like turning the AC on early, making sure windows are closed and keeping doors between rooms open to maximize air flow.

It appears the concept of "temperature split or Delta T" is not just for automotive and RV AC units but for all types of AC systems.