I have a 3 zone carrier infinity system installed about 3 years ago at the start of this winter I started getting a burning plastic type odor from only one zone. (3 rooms) I have been trying to figure out what it could be.. I consulted my hvac guy and he didn't know or wasn't sure. On my own inspection I removed the humidifier to conclude that the smell is not coming from the furnace or coil also b/c then it would be smelling in all zones. I removed all 3 flex ducts from the trunk to see if the smell was in the wall or the trunk (def the trunk) The only thing that it seems can mimic the odor are these little lablels that are adhered to the inside the trunks that say the job # and the part # of each piece of trunk. If not these the only thing I can think of is the foil tape at each duct joint, but the other 2 trunks are built the same way. my question is has anyone encountered this problem and if so how can i fix it and am I on the right path in determining the odor? The odor is only strong when it gets colder outside b/c i assume the heat ramps up more temperature wise. any help on fixing this would be great!!