Auto Air Conditioning & Heater Repair: AC repair, k1500 blazer, chevy k1500

Question
I have 92 z71 Chevy k1500 blazer with a 5.7 motor the fan that blows hot and cold air on inside Will not switch from defroster or floor stay's stuck on vents all the time but I can feel a little  cold air on front window when I try to switch it  from vents to front window I don't here any thing making any noises and also thank's to you i actually have cold air now thank's so much you probably saved me a couple hundred dollars my ac was low on Freon that's why the AC light was blinken on and off

Answer
David,

 The 92 C and K manual HVAC system although fully electronic is fairly simple and easy to diagnose.
 There are three door actuators located on the HVAC box.  One is for temperature blending (blend motor) and one is for air flow direction (mode motor).  The third is a recirculation door that directs air in and out of the vehicle.
 The 1992 system has a fairly archaic but accurate self diagnostic routine that will help you identify what the problem is.  When you select a mode command or temperature command teh programmer (climate control head) looks to see where the motor is on its internal feedback circuit and then makes the appropriate servo command.  
 The motor that we are going to inspect is the mode door actuator.  It has 5 wires connected to it and is located on the left side of the HVAC box.
 First is there any flashing symbols on the climate control head? You have already addressed the AC flashing one. There are two more symbols, a temp cursor and a mode cursor.
 
1.  Reset battery to ensure CCH is not in logic lock
2.  Verify mode selection does not work
3.  Check for flashing messages (yes, identify message, no continue to 4

If you get to this point and it is still not working.

4.  Remove mode door mode actuator while leaving plugged in to harness
5.  Turn key on engine off and actuate mode selector
6.  Observe motor pintle.  Is it moving, ticking, stuttering or doing nothing at all?

Get to this point and continue with diagnosis by responding to me.  I will be available to help you finish this diagnostic proceedure.  From this point on you will need a voltmeter and the basic knowledge of how they operate.

Hope this was helpful!

Wayne