Do It Yourself AC Efficiency Inspection

DIY AC Inspection checks homeowners can do to see if their central air system is working as efficiently as possible. 

Step by step instructions on ruling out AC problems caused by exterior forces, other HVAC companies or age.

If you feel like your central air system isn’t working as efficiently as it should, you can do your own DIY AC Inspection, there are a few simple checks that you as a homeowner can do.

The first thing that you should do is turn the thermostat to cool and turn it down about 10 degrees. You should hear the blower fan on your furnace come on shortly after. Take a walk outside and look at your condenser. You should see the fan turning and hear the low hum of the compressor. Put your hand over the top of the air conditioner. The air should be warm. Visually inspect the fan motor to see if it has been replaced before. When a fan motor or capacitor has been replaced it is often a sign that something else is off with your air conditioner. The fan and compressor may be overworking. Fan motors that are not OEM (replacement parts from the manufacturer) may not spin at the correct RPM and can hold the fan blade in a different spot than what was originally designed. These deviations can cause hard to detect problems on your central air.

While outside, you will see two refrigerant lines. The large one is insulated, pull back the insulation on the fat pipe where the refrigerant line connects to the air conditioner.

The pipe should feel cold like a soda can in the fridge. After a few minutes, it would be normal to see condensation on this refrigerant line. Frost or ice is not normal, do not put your hand on the line at this time, this indicates a problem. Inspect at the coil (the main outer cage like a radiator) and see if it is covered in debris including leaves, cottonwood, webs, dust etc. Make sure to check out the area between the house and the unit as this space gets the most plugged up, without realizing it, debris could be the biggest concern.  Turn the unit off by turning the thermostat to off position, spray with a hose with a nozzle sprayer to clear off buildup. Remember to turn the unit back on after cleaning it.

Inside, during your DIY AC Inspection, check the vents for proper air flow.  Use a small string or a piece of paper to compare the airflow at different spots in your home. A temperature probe ($30) or thermometer is handy to check the coolness of the air. Laser temperature probes such as the one shown are great for this. The air should be 20 degrees colder than the air going in at the return air (the big grills).


Next, go to your furnace room, check your furnace and coil. Does it look like the coil and the furnace were installed at the same time? Inspect the craftsmanship of the metal work and drain lines. Sloppy work is an indicator of other potential issues. Check for signs of water leakage on the floor and underneath the furnace. Water spilling out from underneath the coil is not normal and in any of these areas is not normal. Look at the big refrigerant line (on the coil – main outer cage- of the furnace at the top).  Just like the outside unit, this pipe should feel cold and should not have ice or frost on it. Turn the switch off at the furnace and open the blower door (typically bottom door). With a flashlight look at the squirrel cage (blower fan). If you dare carefully run your finger along one of the fan blades white glove test see how bad the buildup is, anything over 1/8 inch reduces air flow. They should be clean and free of debris. Our technicians should do the dirty work.


Proper Sizing


If you suspect that your central air is undersized for the AC unit already installed, there are somethings that you, as a homeowner, can check. Observe your home from the outside. Look for high sun exposure on the South and West sides of your home. Large trees will help to shade your home from the heat of the sun. Contemplate planting shade trees one or more if possible. If you have more than one story above ground this will increase your heat load. Older homes may have poor insulation. Large windows will let in and trap heat. High vaulted ceilings connected to upstairs areas can be an issue.

Take a rough measurement of the square footage of all above-ground floors, don’t include your garage and basement. Measure the width and length of your home multiply those numbers. A rough guide is 1 ton for every 500 square feet. Central air systems that are undersized or oversized will not work properly. You can find the size of your air conditioner by looking at the model number, usually under the main panel compartment. You should see one of the following numbers:

                24 = 2 tons

                30 = 2.5 tons

                36 = 3 tons

                42 = 3.5 tons

                48 = 4 tons

                60 = 5 tons

The ductwork is often an overlooked part of your HVAC system however it is one of the most crucial considerations. Central air systems are designed for 400 CFM (Cubic Feet per Minute) per ton. If you have a 3-ton system your ductwork should be able to support 1200 CFM. Most homes have 6” round metal ducts going to the vents. These are designed to provide 85 CFM per vent. Count your vents and don’t include the basement ones. You should have a sufficient number of vents for your central air system.

The return air is where the air circulates back into the central air system. These are usually the bigger grills. Measure and record the dimensions of all of them and compare with the sizing chart below to get an idea of if you need more return air. Next, go into the furnace room and measure the return air drop(s). This is the vertical ductwork that connects to the blower compartment of your furnace. Refer to the sizing chart to see if it’s sufficient. 5 ton systems should have a base that allows the air to enter the furnace from the bottom or have return air ducts on both sides entering the blower compartment.

If you suspect that your central air system has some issues or isn’t sized properly contact the professionals at Humphrey Plumbing Heating and Air 802-294-2757. Our technicians have the newest tools of the trade and know how to use them. They are experts at diagnosing problems that may not be apparent to the naked eye.