Unit won't heat or cool--they want to replace defrost panel

by brenda
(Philadelphia)

Lennox. Intermittant problem with the air conditioning not working correctly. It blows cold air for awhile, eventually it just blows coolish air, the house warms up and the humidity in the house builds. I have already had the defrost panel replaced. Now they have by-passed the defrost on the panel but it continues to work the same. Is it possible to have to have the defrost panel changed every year or two?? will it harm the unit to continue to operate in air condition mode with defrost bypassed?