There are several factors that can cause system freezing. Most need to be corrected by your local Lennox Dealer.
A dirty filter can cause restricted airflow, which could contribute to freezing. One thing you can do to prevent or correct freezing is to make sure the filter is clean and replaced on a regular basis. If the filter has been cleaned and replaced regularly but the system is still freezing up, contact your local Lennox Dealer to correct the problem.
In some cases, freezing may be caused by a leak in the refrigerant lines. Low refrigerant levels can cause the evaporator coil to be too cold. In this case, you should contact your Lennox dealer.
Dirty evaporator coil
Over time, the evaporator coil can become dirty. If this happens, airflow may slowly become restricted causing freezing or low cooling performance. At this point, you will need to contact your local Lennox Dealer to correct the problem.
Insufficient fan speed
To prevent freezing, the fan must blow at the proper speed to keep air blowing over the evaporator coil. Should the fan not blow at the optimal speed, your Lennox dealer can correct the problem.