No cool on the only system, 4 years old ac and 2 year old furnace. System is working properly, filter is new and drain line clear. Pressures are good and temperature differential at 18 degrees. Customer replaced filter yesterday, and it was very dirty. Dirty filter give air restriction and can freeze over the evaporator coil, as well. Upstairs is always hotter than downstairs. Thermostat is located in the main level. Sent estimate to zoning the system, and add a thermostat for the upstairs and install a bypass, to balance the pressures, when only one thermostat is calling. Also, signed up customer for home care maintenance. Also, recommend to install an in line switch, to prevent water in the drain pan, in case of drain line get clogged. Drain line was rerouted into the gutter, by other company, and it’s draining properly.