02 Blazer again: same as 01?

Replacing the thermostat did not solve the lack of hot air so I am going in. I have a Haynes which covers S10 and Blazer through 01,
cannot find Haynes or Chiltons for 02 and later. Don't want to pay big bucks for the shop manual or even 50 for the generic Chiltons. Two questions: 1) Was there a significant model change in 02? None of the pictures look familiar but of course they are all of the PU, of course.
2) The Haynes has no mention of the air control doors just removal and replacement of the heater control switch. Anyone familiar with getting to the actual doors that contol air flow from fresh, cool , hot? Is it likely to be the switch or the door? Should I look for a vacuum leak? Guess that's more than 2 questions, sorry.
Thanks in advance and thanks to all who replied about the radiator drain. Bob
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