The fan stopped working for the rear AC/heat in our 2003 odyssey. Checked 40amp suqare fuse under hood and it tested ok. Is there a fuse or breaker for the rear fan motor?

The large fuse you checked is for the rear fan blower motor. The fuse you need to check is for the fan motor relays and rear mode control motor. It is fuse No. 3 (7.5A) located in the driver's under dash kick panel fuse box.

If fuse No. 3 is blown and you replace the fuse and it blows immediately, you'll have to check the five relays and the mode control motor all located near the rear A/C unit in the right aft sidewall. Most likely, the mode control doors have become jammed and that is why the fuse blows. The doors shift air from overhead vents (cool) to floor vents (heat).

If the fuse is fine, the trouble is probably with the blower motor itself or the wiring to the blower motor is broken, or there is a bad ground.