Ok. I started out check the operation of the blend door. Removed the lower panels at the underside of dash and part of the lower plenum. Two screws. I moved the selector switch and watched the blend door as it went through its different settings. It worked and stopped at all different locations as I moved through the dial. The air never got warmer. There is no electric actuator on mine or if there is its not accessible through the glove compartment the glove compartment is part of the dash. There are relays in the back thats it. I removed the door all together. From under the passenger side I did see a vacuum actuator with an orange line to it. No matter what position I put the switch in that selects air location that actuator would not move. No vacuum out of it. I put my vacuum pump on it and you could here it move something Im not sure what. It made a lot of air noise with the suction pump attached. The amount of air coming out of the ducts though is not like it used to be and its ambient temp. After looking at this whole problem more I have another problem maybe related. The temp gauge never moves from low. If I open the radiator cap there is no pressure and I see no movement of fluid in the radiator. I replaced the radiator about 3 years ago because it was clogged with Dexcool. Is it possible the no heat problem is another clogged radiator? Wouldn't it over heat? I can grab each radiator hose while running and there hot but not that hot. No pressure. I can squish water back and forth by squeezing one hose at a time back and forth. I know the fan motor now is going I hear a bearing squealing but it seams to be working through out the settings. I was so mad at my son that he hadn't told me about these things earlier that now its hard to diagnose. I'm going to try to back flush the heater core now and see if that helps with the heat problem. It looks like I will have to pull the dash to get to the selector switch. If you smart guys have ideas feel free to let me know. I will post back with results after heater core is flushed. Just checked the diagram and orange vacuum line works plenum side vent activator is that outside air is that why it makes more noise its opening to the outside?

 

The same blend door actuator has been used on various GM vehicles since 1991: Dorman - OE Solutions HVAC Air Door Actuator 604-100: Advance Auto Parts= Your 96 is equipped with one.

The orange line goes to the recirculation door which is located next to the "A" pillar under the extreme right side of the dash. It directs inlet air flow from either the cowl, or recirculates the inside air. On the chart it is port #5 and only has vacuum in the MAX AC mode switch position. When the actuator has vacuum, the air flow noise level under the dash increases, (normal).

Normal engine coolant operating temperature should be ~198F. The upper radiator hose, at the thermostat outlet, should be very close to that temp.

Both hoses at the heater core should be nearly the same temp. Too warm to hold with bare hands for more than a few seconds. If you notice a difference in temperature, the core is clogged. It will either need to be flushed, or replaced.

During your vacuum test, did air flow exit where it is supposed to?

 

Ok just finished flushing the heater core. It gets warm air now. Everything is working including the re-circulation. The only thing that doesnt work is the amount of air coming from the ducts when the temperature control dial is in hot position. The colder I place it the more air comes out. In fact if I place the unit in max air but with the temperature control at hot I get the amount of air that should be coming out of the vents. Is there an actuator that is activated when you change from colder to hotter? I can take a picture of my glove compartment but the only thing you can see in there are the relays behind a little panel. Am I missing something.

Also my system doesn't seem to be pressurized. I can open the cap anytime and no fluid will come out and there doesn't seem to be any movement. Im going to replace the cap and see if it holds pressure. There is no fluid loss and no leaks? Is it possible that crappy Dexcool has clogged the radiator or would that cause overheating? The temp gauge doesnt seem to move from low a little above 100 degrees. I can hold onto the heater hoses or the radiator hoses without letting go.

Were expecting ice and snow tomorrow. Great

Again Thanks for your help.

 

Sounds like there's a restriction in the inlet air duct from the cowl. The only thing that changes when you select MAX AC, is where the system gets its inlet air from. Might want to pull the cowl & wiper blades off and take a look in there for debris, leaves, mouse house, etc. On the passenger side you'll see an opening, Take Mom's brand new Dyson in the garage and clean the cowl out She'll love ya for it

EDIT: "The temp gauge never moves from low."

That's a problem, probably needs a new thermostat.

 

You think the thermostat is stuck open? Thats why it never has a chance to get hot? Good thought.

"The only thing that changes when you select MAX AC, is where the system gets its inlet air from." Is there an actuator that allows that to happen? How does it mix the hot and cold?

 

Thermostat probably stuck open not allowing the engine to reach normal operating temperature.

The actuator with the orange vacuum line is what determines where the system gets its inlet air, (recirc door). Reference diagram on right in post #3.

Post #3 again: Shows the blend door with the electronic actuatror. The door is between the evaporator and the heater core.

EDIT: Keep in mind, the vehicle heater case does not look like the drawing. It is for illustration purposes only.

 

Captain Hook
Your probably right then something is blocking the air inlet. My son lives in a heavily wooded area. Sticks leaves rodent a good possibility. Thermostat and a good cleaning of the cowl area next on the list.
Thanks again.

Are there any posts with pictures that show the electric actuator? Ive seen what its supposed to look like but if it is supposed to be see behind the glove compartment I dont see it.?

 

It's definitely "neatly tucked out of the way" Couldn't find a video for 1996, but this one will give you a good idea where to find it:

 

Captain Hook
That is not how my opening looks. His sleeve of the glove compartment is riveted in to the dash. It is actually part of the dash. This and maybe the 98 the glove compartment is contained all in the door. So once the door is removed you have the access shown in the video. GM may have changed it after 96 to make things cheaper and access easier. I did see a change in shop time bulletin somewhere where they altered the warranty time because they found the dealer could do it cheaper without removing the dash.I will take a picture and post it tomorrow when he brings the car over again. When he drove it home last night he said he got heat and the temp gauge got up mid range now. He is not mechanically inclined and so without me monitoring it its hard to explain second hand. I will see on Sunday. I did see though all day yesterday that the needle on temp was not much above the lowest setting. I will though change out the thermostat.

 

Changed out the thermostat. Tried to get an AC but couldn't find anyone that had one. I looked on the old and new and it wasn't marked. They used to tell the temp on them. The heat is working very well now only sits at about 170 degrees but its about 30 degrees so will see. I bet the one they gave me was a 180 degree. I pulled the cowl screen to clean out the crap in there and it was clean. Because of the age and gold it broke. The screws are those plastic one that go into plastic anchors going through the holes in the support for the cowl. Where is the best place to get a new one and those screws and anchors only available through Chevy? The blower motor still needs to be replaced but that will be another day. The bearing is making noise. There is not as much air coming from the center vents with heat as there is with AC but im not going to take the dash apart in the winter if not needed.

I removed about a half gallon of antifreeze to replace the thermostat does that sound right? It took only a half gallon to fill it again. In the past I remember having to remove more. ??

Thanks so much for your help.