I hear this question often, so I though it might be helpful to outline the process I usually follow to inspect the Air Conditioning System. Because I do not want to bore you, I will not mention every little step that actually takes place. I hope this provides you with a good overview of what the inspection entails.
Run the Unit for a Minimum 2 Hours
One of the very first things I do when I arrive at the inspection is locate all thermostats and turn on the cooling system. I usually let the AC run for the entire inspection, which is around 3 hours. You’d be surprised how many times I’ve seen issues pop up after the system has been on for over an hour! Sometimes the unit performs as intended for an hour and a half then suddenly starts dropping water into the safety pan or not cooling as efficiently.
Inspecting the Exterior Unit & Electrical
The next time I cross the AC system will be on the exterior walk around, where I will record all model numbers and serial numbers for inclusion in my report and make note of the size of the exterior units. Other important thing to take into consideration here are the condition of the refrigerant lines and the condition of the unit itself. I also record information about how much amperage the unit pulls under normal working conditions and the manufacturer’s recommendation for the breaker that should be in the main electrical panel. When I inspect the main electrical panel, I will verify that the breaker and branch wires are sized according to manufacturer’s recommendations.
Inspecting the Interior Unit & System Performance
The next time I see the AC system is whenever I cross the interior portion of the unit. This can be in many different locations, but it is most typically in a hall closet or in the attic. There are many inspections points here that you probably don’t care too much about, so I’ll just hit the main points. If the evaporator coil is accessible, I will inspect it for damage or debris. I verify that combustion, exhaust, and drainage lines are correct. I record any signs of current issues as well as indications of previous issues. I measure the difference between the air going into the unit and the cooled air coming out of the unit. Some time near the end of the inspection, I use a laser thermometer to register the air temperature at every register in the house to be sure that every room is getting air at a satisfactory temperature.
Obvious visible deficiencies aside, I think that most home inspectors will tell you that the most important indicator of how your system is performing is temperature differential: what is the difference between the air going into the unit and the air coming out? After all, this is what the unit is here for. In my opinion, running the unit for an extended period of time is also crucial. I want to know how the unit will react to being on for 2 straight hours, because this is what I believe my customer wants to know. There are no guarantees, but if the unit is able to meet cooling requirements for over two hours then that unit is performing as it was intended to, at least on this day.