I discovered this possibility this weekend. I had removed my furnace's blow er for cleaning. When re-installing the blower, I accidentally did not plug in the multi-colored wire bundle. The blower ran constantly without heat u ntil I figured out my mistake.
As an aside, in the three condos/houses I have owned over 20 years, I had n ever cleaned the furnace blowers. I did the taxes for an HVAC technician th e other week, as part of a community service gig. We were chattering about HVAC design as I did his taxes. He said cleaning the blower was some of the best major preventive maintenance one could do for a furnace. This weekend , I went at it. My condo's blower was filthy -- full of dust, dirt and fluf f. I took it outside, both vacuumed and blew it out with low-pressure air, sprayed Simple Green on the blades and wiped them, and used a lot of Q-Tips . Then I re-installed it. What a difference. The air the furnace blows is n ow odorless. There seems to be less dust in the condo, and I think it warms up more quickly.