Looking at the trouble shooting information that Walt supplied the link for, on page 4 / page 9 printed on bottom of page.
It looks like one accesses the furnace by removing the outside cover and the required parts to get to the circuit board and blower assembly. Should it be installed with the extensions, then one would need to remove unit to get to the back. Check the drawings for your setup.
They do not make getting to some of the items easy!
Look at the flow chart on page 14 as printed on the bottom of the page / or page 9 on the page display window.
The PDF version looks to be a copy of only some of the pages from the original manual!!
Follow it through the indicated steps.
You did mention the the blower does not start and that is the first step in the sequence up to the point the furnace flame lights.
Tried to copy Step A page18 / page 13 from the header bar.
If section does not copy over. Look at item # 4 and 5. the key might be locating the defective relay if that is the case or replacing the motor.
The other issue could be an open circuit brake or fuse mentioned in the information.
Figure 16 on page 16 shows the time delay relay that could be bad and it would keep the blower motor from starting. Once the blower starts the sail switch should close and the furnace should come on if everything else is in order.
Download the information at this link. Looks like what you have described in your post.