I fixed it! I finally replaced the A/C and heater blower motor in the van.
The blower motor went out during our family vacation in July, while on the road through Navada with a van load of kids. Not fun. I took out the old one a month or so back only to discover I’d purchased not the primary motor, but the auxiliary blower motor (for the back of the van) by mistake. We finally bought the correct motor last night and I installed it this afternoon after school. And it works!
Tomorrow the girls and I will actually have heat on our drive to school.