Doesn't work heater nor a/c

http://www.vadengmpp.com/owners-manual/gmc/2003-GMC-Sierra.pdf

What about the window motor?

The most likely culprit is your driver's door control module... it's built into the driver's window switches. Double-check all your fuses before replacing any parts.

if the blower motor motor is working then its a blocked heater core or a faulty shut off valve ,i would need to get my head under the bonnet and then the dash to find the fault to be honest

Hello roesusie: My name is Roger and I will answer for you. In 2003 GMC did not put a cabin air filter in the 1500 or Denali trucks. There is no openings in the heater case for a filter. Some one would have to physically cut the heater case to install it. Sorry I could not give you the answer you wanted. Should you need further help please just ask. Please rate the answer as this way I know it was helpful.Thank You for using Fix Ya. Roger

no,, the system works from a vacuum and has to be worked on in a service garage. sorry about the bad news...

no it solidored to a cuircut board, soory. good luck.

There is no fuse on a block heater. It is an extension cord with a resistor (element) on the end (see photo. If it not working, the resistor (coil) has failed. A new block heater is required.
Before replacing, however, check the outlet and/or beaker the outlet is on to see if it has tripped.
I too live in s/e Michigan, and it was -19 this am. No block heater can keep up with these extreme temps.
:)

My 2003 Sierra's blower came on by itself in the garage while I was sleeping and ran the battery completely down. I had to replace the blower switch located under the glove box next to the blower at the bottom of the right corner of the dash. The switch is in front of the blower and held in by two screws. Disconnect the two wire connections. This is a "dealer only" part and cost me 65.00. Also check the wire harness with seven wires connected to it for melted plastic. It will be marked "ABCDEFG". If it has melted, you'll need to replace it. Pay attention when reinstalling either part, that the wires "ABCDEFG" match the switch in that order.

Check or have checked the blower motor resistor. These resistors will cause this problem. I would go this route first as these are relatively inexpensive and usually the problem.