Last week we discussed the definition of Temperature Differential, or Delta T, but how do we know when the system is operating within an acceptable range...

True or False? An air conditioning Delta T or Temperature Differential of 28 degrees is better than a Delta T of 18 degrees.

FALSE- A Delta T of 28 degrees is NOT better than a Delta T of 18 degrees. Most folks responded correctly, but I want to make sure you understand why. As we discussed last week, the normal acceptable range for Temperature Differential is between 14 and 21 degrees, and performance outside of the acceptable range shows the system needs service. Colder is not necessarily better. Typically, when the Delta T is GREATER than the acceptable range, it indicates that air is staying in the return compartment (inside a/c unit) too long and cooling too much. This could be the result of a blocked filter, or contaminated A-Coil or faulty air handler fan. Inversely, when the Delta T is LESS than the acceptable range, typically the problem is with the condensing coil (outside a/c unit). The problem could be low coolant, bad compressor or restricted air flow over the outside coils. When the Delta T is outside the acceptable range, either high or low, the system is not operating as intended and the system needs to be reviewed and corrected by professional HVAC service personnel.

Bond Whitfield of The Hutchison Group