Palf70step all the way to the top on all three is the neutral or off position. Left side is defrost when it's all the way down it closes the baffle so all the air goes to the windshield to defrost, all the way up and the baffle lets all the air go to warm the feet. Right side adjusts the temp up and down the top is off, down is hot. The center control is the fan speed at top is off down a bit is low then medium then high all the way down. The workshop manual might have some info on the heaters I can't say for sure cause my knowledge comes from working on GM stuff for years it's been the same for a long time I believe. Hope that helps any....Vernski
