As a home inspector in one of the hottest climates in the world, determining the condition of the air conditioning system for my clients is a top priority. Summer temperatures routinely exceed 115 degrees Fahrenheit during the day and may still be above 100 at dawn. A recent home inspection I performed in Chandler, Arizona (home to the Chandler Chuck Wagon Cook-Off Festival every November) revealed a problem with the air conditioning system. The home was only two years old, so the air conditioning should be good as new, right? You'd be wrong. About 15 percent (my estimate based on my inspection history) of the one and two year old homes that I inspect have a problem with "Not cooling enough". This was the case in Chandler.
A Home Inspector is not an Air Conditioning contractor. Kind of like how a family doctor (generalist) is not a Brain Surgeon (specialist). I therefore perform a very limited and general evaluation of the cooling system. If I don't think it's cooling enough, my job is to recommend to my client that a licensed HVAC contractor look into the matter and suggest a repair cost. They have special tools and advanced training to help them make a very accurate diagnosis.
So how do I determine that it is "not cooling enough"? I measure the difference in temperature between the system air intake (at the filter) and the supply air register (at the coldest air register) using an infrared thermometer. This measurement in itself has limitations, as it is not a measurement of the air temperature but a measurement of the surface temperature of the grill that I am pointing to. It is a very general indication of how the system is performing. If the difference in temperature between the two readings (this is known as the "split" temp) is less than 14 degrees, then something is wrong and I recommend evaluation by a specialist. In this example the split temperature was only 11.5 degrees (70.5 - 69.0).
The specialist will use advanced tools and training to determine the exact performance of the system based on air flow, wet bulb and dry bulb temperatures, and other readings. In my climate area (a desert), this method works for me, as it is very rare that a problem is not found by the specialist when I have called for further evaluation and repair based on a split temperature below 14 F. The most common issue for a low split in systems under two years old? (based on my inspection history): Low refrigerant with no leaks found, meaning it was charged low when installed, followed closely by incorrect fan speed, also set incorrectly when installed. This particular unit had a low refrigerant charge.
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