Quoting Saffy Sly:" Um. When ours did that, it was because the compressor in the furnace needed replacing. "
I keep reading AUX is a normal thing for certain temperatures, its like backup heat when the normal heat can't get warm enough to keep up. But it looks like if that was the case it'd at least still blow out warm air. Ugh. Always something for us. Guess I'll have to call the landlord.