I just got a 99 blazer LT last year and it has been a headache with this AC. I have the auto climate control and when the ac is turned on it just goes from full heat to full cold repeatedly. I have had the guy I bought it from look at it for me multiple times and he has put a new compressor on it just recently but it still has this problem. Reading on here I thought it might have been the interior ambient air sensor not working but that was replaced and I still have the same problem. The truck holds freon and the system seems to work great because it really puts out the heat and really puts out the cold. Now I just need to stop this blend door from moving back and forth. We removed the "cut here for maintenance piece under the hood and we can see the blend door moving back and forth repeatedly. Anyone have this happen or any ideas? I read something about pulling the B+ fuse to remedy this problem but I cannot find where this is. Any help will be greatly appreciated!

 

Try this: with the key off remove the RDO BATT fuse from the IP fuse panel for 15 seconds. Put it back in, turn the key on without starting for 45 seconds. The door should be cycling when you do this, this is how it finds it's range limits. If it keeps on cycling (as it's been doing) I'd guess the sensor part of the air temperature actuator is bad or the Electronic Climate Control module is bad.

 

I tried what you said multiple times with no luck. For right now I just have a piece of wood I cut in between the door and the side so the door stays open on the cool side. What is needed to figure out which component of the ac system would be bad? I dont want to pull both parts if one or both are still good.