Heater control does not work heat always comes out of dash vents no matter what the setting. no defroster, no foot level heat. how do I get to the air diverter that changes the direction of air. the switch seems to be working based on lights for recirculation etc.

does the car have automatic climate control?

I assume your heater setting is electric control, if so either your defrost and floor heat switch failed or wire problem. For the air not hot, check the heat control valve on the top of the hose it should be in front of the firewall. I don't know your car is using mechanic valve or electric control valve. Anyway check there first. Good luck.

Could be a problem with the control on the dash or a blend door under the dash.

The head control in the dash is most likely the problem,the control in the dash,will have to be replaced.,only thing you can try would be to disconnect the negative battery cable for 10 seconds and put it back on,then turn the ignition on,then start,see if the controller starts to work again,if not replace the head.

The HVAC mode selections on these are controlled by an electric stepper motor that receives commands from the BCM (body control module). The BCM decides where the air door should be by looking at where the dash control input is.
Each mode selected has a different resistance level. From low resistance to high resistance: Panel, Bi-Level, Floor, Mix and Defrost, with Defrost as the highest resistance (~100K ohms). A high resistance or open circuit would probably default the system to defrost no matter what position the mode control was set to.
If the control is dirty or there is a connection issue, this could cause this problem. Does playing with the control make any difference?
The BCM can store fault codes with HVAC releated information. The system can be reset and recalibrated with a battery disconnect, this will also erase any fault codes.
I would start by looking at the dash mode control.

Good luck, i hope this helps.

Sounds like a faulty mode door actuator for the a/c in the dash. There are a series of mode doors that controls air temperature and air flow. They are located in the passenger side of the dash. If the temperature mode door isn't closing all the way then when you could still be getting heated air from the heater core when on A/C. The blowing only out of the defrost is a textbook sign of a bad mode door actuator.

Sounds like a vacuum motor problem which controls the blend door and its position inside the dash board area where the flapper directs air from the heater core to the defrost vents or the vents, or the floor, as directed by climate controllers on the dash. Good luck on this repair.

The problem is probably a faulty diverter door actuator or vacuum problem at the HVAC plenum under the dash. This is a common problem - see YouTube for help diagnosing this:
https://www.youtube.com/watch?v=Nlt9A1sp-4U

The controls for your heater/vent selection is inside the dash, behind the control switches you use to select the vents the heat/AC will come out.
When you move the selection levers, there's a few things that happen. Vacuum is applied to the doors (which are inside) and they open or they work using cables to move the doors or both. The different doors open, directing air flow to the vents selected.
Remove the controls from the dash (which should just be removing some screws, maybe a few small pieces of dash and pulling it out). The controls will be connected inside so they will not come out very far.
Just check to see if anything is disconnected and try operateing the controls with the heat on to see how they work.
Sometimes they just stick or the doors stick. This system is the way the 1991 models worked but since they are the exact same, it should be this way also.
Look it up in some sort of repair manual for more info. I find with these trucks, they don't heat very well using the front vents anyway. I find using the bottom vents work best for heat unless you need defrost.
The "heater" selection will atomatically use the bottom vents, "bi-level" AC will use the front and bottom vents if I remember right and regular AC will automatically use the front vents. For the trouble in removing these controls (the whole dash would need to be removed for repair) I probably would just live with the way they work if they do work atleast properly (enough heat and AC). If you find that you don't get enough heat or AC when in use, check the cooling system for proper operation and blockages/mineral buildup and check the AC system incase it needs recharging or you have leaks.

Check the control cable that operates the diverter door in the heater box at both ends, to make sure that it operates the door when you move the control lever.