I have an approximately ten-year old Trane XE80 HVAC in the attic above the second floor of my house (cools and heats the 2nd floor). It does not operate properly--yesterday and last night, the blower would not come on in response to the thermostat. The outside compressor unit runs when the thermostat commands it to, but no blower. I also couldn't get the blower fan to come on when I switched the "Auto/On" switch to the "On" position. I checked the house electrical panel--no breakers tripped. I also checked the HVAC unit itself in the attic--the red LED was blinking slowly and didn't appear to be sending a trouble code according to the owners manual. I turned off power to the HVAC unit and back on to reset, but still no blower function. This seems to be an intermittent problem, I remember this happening once before and it corrected itself.

Could be a bad motor
Check for power at the motor when the unit is supposed to be running.
Also if that unit has a separate blower relay that can also cause a problem
If the motor checks goo you could also have a bad circuit board.

If you do not know how to check these items I suggest you call for Professional ON SITE service.