1996 Blazer 4.3. 215,000 kms.
Replaced the DREADED blend door actuator. This job is not fun but also not impossible. Basically just had to keep pulling stuff off until I could get to it. It will take an afternoon and a bit more to complete. Had to walk away a few times and count to ten!!
I had the same 'no heat issue'. I started with repacing the thermostat. No change. Then replaced all the vacuum hoses. No change. I knew it was not the heater core, so I left that alone. Next I tried replacing the temperature control switch. No change. Then I went after the blend door actuator. A lot of people shy away from this but go ahead and do it if you have some basic knowledge and some basic tools.
I broke my hazard switch during the operation and replaced it no problem (easy fix). Now that everything is said and done, only problem I have is that the turn signals (and hazard) do not work. I checked the fuses and they are OK. Any ideas? Is there an electrical connection under the dash I may have forgot about?