My furnace,exhaust keeps icing up, what can be done?

Question

It is a Carrier furnace, 12 years old, high efficientcy, has PCV exhaust.

Answer 1

I've never heard of this, my daughter has this and hers doesn't ice up. However, I suppose if you have a lot of condensation, it might. That would be the clue, condensation. Where is it coming from?

If you have a humidifier hooked up recently that you forgot about, that may be it or some form of moisture forming thing, that is emitting enough vapor to expel this vapor into the exhaust system and thus ice in the opening.