My son and I took apart a non-working heater blower motor to see about repairing it. If you have never opened one up, you may find this to be interesting.

1990 Jaguar Sovereign : Disassemble the Heater Blower | AndyRupert.com

 

Just watched your dis-assembly video Andy - the relays inside the housing are not actually all that standard - these blue Hella relays have internal diodes. There's a few good threads on the forum about modifying radio-shack relays using a diode soldered on the outside - that's what I did on mine.

If you're going to completely rebuild the blower you should also take a look at the speed control transistor circuitry, it's accessible by drilling out the three pop-rivets. If a fan only blows on high it's usually because the speed control circuit has a problem. One of the relays is used for high speed fan and by-passes the speed controller.

I replaced the darlington transistor and all the other components on the speed control circuit board when I replaced the relays.

Check out the threads on the blower repairs, there are quite a few detailed postings.