it does this all the time
blower motor only works on 4 on 2007 Chevrolet Colorado
repl blower motor resistor,when they go bad they default to high and thats what you have. they cost approx 15.00 at the dealer and are easy to repl. its located under the glove box area
Mine did the same. I replaced only the blower control & it worked for about 2 weeks then stopped working. Had to replace the blower control & the resistor. Been about a year & still working.