We have a Lennox Elite Series gas furnace, MN # G23Q3/4 100-2 Model. w/Central Air. The blower comes on and starts blowing cold air and approx 30 minutes to an hour later will blow out warm air. We thought it was a faulty thermostat (White Rogers brand) so we put a new one on. The furnace is doing the same thing. We have even cranked the temperature up to 80 degrees and it still blows cold and then an hour or so later it kicks out heat. This happens off and on throughout the day. Can you help please? Thank you.

P.S. Our problems with this 10 yr old furnace started shortly after a power outage, that changed to a brown out for several hours. Could this be part of the problem?

Power outage is not the problem. It is the surge of power when it comes back on. My best advice is to call for service. I say that because lennox do have problems and it will be over your head to try to fix it. Not being smart here just stating the facts.

Have you figured out the problem yet? I know this is a couple of years later, but I am having the same issue. Cold air is blown, then a little bit of warm air, and then once the house is finally warm, it starts blowing cold air out again and chills the entire place. What is this all about?