We bought a new house with two Lennox a/c systems. The one upstairs has not been able to keep up during these 100 degree days. I have the thermostat set at 77 and both days this weekend the temperature rose to 79 inside the house. I've notice that the cold line is not cold and sweaty like the downstairs unit. The temperature out of the closest vent was 66 as it was 61 downstairs. Now at night it seems to cool just fine and the temp goes down to 60 degrees. Both units are in the attic. I am going to call the folks that installed it to take a look, but I first wanted to get some opinions. Is it low on refrigerant, return not sealed so pulling in attic air, etc.