The heater - AC blower motor may stop working at one or more speeds due to a faulty blower motor resistor block.Google+
Car Problem Reports
Chevrolet Colorado AC Blower Not Working Correctly Due to Failed Resistor
Chevrolet Colorado Problem
Average Mileage: 85,102 mi (11,000 mi - 246,546 mi)
Visitor, 2005 Chevrolet Colorado, 48,000 mi
Blower motor has only worked on high #4 since I had 42000 miles on the truck. If I wiggle the warning harness under the glove box, 1 & 2 will work until I hit a bump or stop suddenly. I have a harness but am fearful of putting it in due to the passenger airbags!
Visitor, 2004 Chevrolet Colorado, 85,000 mi
The blower only works on level 4.
Visitor, 2005 Chevrolet Colorado, 63,100 mi
I have replaced the Resistor pack 3 times. On the 2nd time I even did the wiring harness. Now it is out again, plus the Flashers, Aux ports, AC will not turn on, etc. Too many electrical problems to list.
Visitor, 2005 Chevrolet Colorado, 84,000 mi
ac blower only works on1 2 4not 3rd
Visitor, 2005 Chevrolet Colorado, 107,000 mi
fan blower stops working in range 1 thru 3 intermittently
Visitor, 2004 Chevrolet Colorado, 87,000 mi
AC/Heater blower motor only works on level 4 (highest speed). haven't fixed it yet.
Visitor, 2004 Chevrolet Colorado, 75,000 mi
I have had this problem 3 times since I bought the truck in 2004. The blower would quit working on all speeds except high
Visitor, 2004 Chevrolet Colorado, 60,000 mi
Blower motor only worked on settings 0 and 4. If set in between, freon continues to circulate through the system without any cool air being blown into the cabin. I went through 2 resistors before realizing the wiring harness has a tendancy to come lose. I found that if I jiggle the harness when the blower is failing, it'll resume working at the in-between settings.
Visitor, 2007 Chevrolet Colorado, 39,000 mi
It started at 39000 and i have 55,000
switch only works in 4th position
Visitor, 2004 Chevrolet Colorado, 139,000 mi
I have had this problem for the last 2 years and I had it fixed last year and it lasted 2 months.