Morris Heat and Air offers new home inspections and annual service for air conditioners. Sadly, we run into the same problems over and over again in Northeast Oklahoma. One of the main problems we find is that the blower speed is not adjusted correctly for the HVAC system. All Air Conditioners work the same. They cool the air 18-25 degrees. This means that if you measure the air going into your unit and the air going out of the unit, you should see an 18-25 degree drop in temperature from the return air to the supply air at the unit. In this example I would like to use a real life example from a new construction home in Broken Arrow Oklahoma.
The upstairs air conditioner on this particular unit is a Lennox 2.5 ton condenser Model ML14XC1S030-230A04
a 2.5 ton air conditioner should have an airflow rate of 400 cfm per ton +/- 10% which would mean a range of 900 CFM to 1100 CFM with the mid range being closer to 1000 CFM for this particular Lennox 2.5 ton air conditioner.
When I first visited this home and measured the return and supply air delta T (Termperature Difference) at the unit, I measured 14.94 degrees Fahrenheit Delta T. This is not adequate as a properly operating air conditioner should be cooling the air 18-25 degrees. This can be due to incompatible equipment, dirty coils, a low refrigerant level due to a leak or never being charged correctly or it can be due to higher than usual fan movement across your evaporator coil.
Upon further investigation, I found that the cooling mode for the 2.5 ton system had a fan speed setting of HIGH. This particular Lennox Furnace Model ML196UH070XE36B-52 has a fan speed capability of 1315 CFM at .5″wc. When a new system is installed, because the fan speed capabilities of a furnace can accommodate several different sized air conditioners, the fan speed must be changed to accommodate the air conditioner installed. In This case we have a 2.5 ton air conditioner. This means that the installation company did not adjust the fan speed at installation and should have set the fan speed to Medium-Low which moves the air at a rate of 1020 CFM at .5″wc. After adjusting the fan speed for this furnace to the appropriate fan speed setting, now the air conditioner upstairs is cooling the air 18 degrees Fahrenheit instead of 14.94 degrees Fahrenheit. The problem is fixed. Below are the before and after images of the return air and supply air temperatures before and after.
In Lennox equipment we have found that they do not include the blower performance tables needed to accurately know the blower performance of the Lennox unit in question. These are found in a separate manual known as a Lennox Specifications Manual. You can access the full Lennox Specifications Manual for Model ML196UH by clicking HERE.
You can also access the Lennox Installation Manual for Model ML196UH by clicking HERE.
It is very important that your fan speed be adjusted on your HVAC system to ensure that your Air Conditioner is properly cooling the air 18-25 degrees. If your air conditioner is not cooling the air at least 18 degrees, your unit will run for longer periods of time and will use more energy. If your unit runs for longer periods of time due to a low temperature differential, it will wear out prematurely, break down more frequently and use more energy than it would if installed properly. At Morris Heat and Air in Okmulgee Oklahoma, we believe that all air conditioners should be installed properly and we specialize in ensuring that they are. To set up an appointment with us to do an inspection, call us today at (918) 734-0040 or email us at morrisheatandair@gmail.com