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My 1981 is having some hvac issues. I had not driven it for several years, now I'm trying to get everything back in working order.
The first problem was I was only getting hot air from the HVAC. I'm pretty confident the A/C doesn't work, but even when the air outside was relatively cool, I was getting only hot air. I found some info in forums on the web about the cable between the HVAC controls and a spot up behind the glove box. After looking at that, I found and fixed one problem, in that the little switch was not being contacted. After messing with the turnbuckle, it is now being contacted. That should solve the "only hot air" problem. See videos:
The other problem is I only get air from the floor vents. I traced as much of the vacuum hoses as I could under the hood and behind the center console and glove box, and didn't find any obvious problems. However, while messing with the "hot air" problem, I saw that the main vent duct behind the center gauges is not on properly. Judging from the amount of funk around the area, it's probably been like that for a looonnnggg time. Since I couldn't pry it back to adjust it so it mates properly, I will probably clean the area and put some HVAC silver tape over/around that area to seal it better. I hope that solves the problem with no/weak air coming from the dash vents. See below:
Pic.
I'd like some opinions on the HVAC switch itself. I seem like it's pretty sloppy, and I'm not sure if it's just 1981 chevy engineering, or it's a problem that needs to be addressed. Please take a look at the video below and let me know if this looks ok/normal. There's a gap, or slop, between the white piece and to the right (hose side) of the switch. I suppose if everything works ok, it's not a problem, but if my tape job from the problem above doesn't fix things, I think replacing the HVAC switch is the next step.
Sounds like you have adjusted the heater control valve switch correctly. All that switch does is open/close the heater control valve under the hood using vacuum. If you still have heat coming through your vents no matter what position the Heat/Cold lever is in, then you may need to replace the heater control valve if you haven't done it yet.
Now if nothing seems to be working as far as switching from ac vents to defroster to floor, then that control switch in your last video needs replaced. They are know to go bad and will leak vacuum so none of the valves can switch. If you have a vacuum pump, you can actually apply vacuum to each valve directly to test that each valve is working.
Oh and there should be just a couple of bolts that hold those two pieces together on the second picture if it is where I think it is. They were not great fitting from the factory but you can take some time like you plan and seal them up better.
Last edited by MattoonVette; Aug 25, 2019 at 09:28 AM.
If you're talking about the duct behind the gauge pack that leads up to the defroster it DOES NOT MATE with the defroster duct! There's about a 1/2" gap. Some say it was extremely sloppy engineering. I suspect it's intentional and allows some hot air to go to the very rear of the dash where it helps to heat that huge windshield wiper well.
If the vacuum selector switch is leaking I completely agree with the above! Mine was leaking and I bought the "modified to not leak" version from one of the vendors. Guess what? It leaked! I took the original apart, cleaned it and put in some silicon grease. PERFECT!
This occurred after replacing ALL of the vacuum and fuel vapor hoses using Doc Rebuild kits. The only hose I didn't replace was the tiny connection at the modulator valve on my automatic transmission. Guess what? It failed at the end of my longest to date drive (about 300 miles).
Well, what I tried so far hasn't helped, so I have a selector switch on order. I guess I could pull the original one and see if I can do anything with it. I'll post back when I have some answers.
Check the heater control valve in the engine compartment. The valve is on the passenger side of the engine compartment, down low near the AC drier. Pull the vacuum line at that point and put a vacuum gauge on it. If you get vacuum there it works. Then replace the heater control valve. When I went to check mine I found that the small metal nipple on the control valve had rusted and broken off. Replaced the valve and problem solved.
So I have the replacement HVAC controller. The electrical connections don't look like the stock that's in the car right now.
Here is the one in the car, which should be the original. You can see I've removed the gray 4 pin connector from the controller, and it's now behind the 4 pins on the controller. Behind that is a 2 pin connector:
And here is the new one from Ecklers:
You can see the electrical connections are different. All places I look for on line have that same replacement controller. Does that mean no one sells the right one?
The black four pin part you are showing in the first picture is the rear window defogger switch. It is a completely separate part from the AC controller. Behind the defogger switch is a black connector, it is the one that goes to the AC controller fan speed switch.The part you show in your second picture is the correct AC controller. Look in from the passengers side of the console and you will see it better.
Last edited by MattoonVette; Sep 8, 2019 at 02:29 PM.
The black four pin part you are showing in the first picture is the rear window defogger switch. It is a completely separate part from the AC controller. Behind the defogger switch is a black connector, it is the one that goes to the AC controller fan speed switch.The part you show in your second picture is the correct AC controller. Look in from the passengers side of the console and you will see it better.
Ok, I pulled the center console up some more and I can see what you're talking about. I've got the right HVAC controller, and now just need to pull the old one out.
Ok, so I got the old one out and new one in. I won't test it until I'm done fussing with the cigarette lighter and put the console back in place. Here's some pics of the old HVAC controller.
Note in the third pic the gap between the white part and the part it's below (in the pic orientation)...I'm guessing that isn't supposed to be like that and may be part of the problem.
Black Vacuum Hose
Dont want to start a new thread for this but anyone know where this vacuum hose is supposed to connect on an 81. I think its the source connection for the HVAC its coming out of the firewall behind the distributor. There is a capped hose part of the headlight hoses? Its also much smaller diameter than the other hoses.
I'm pretty sure that's the hose that connects to the hot water bypass valve. When the temperature selector is all the way to "cold" it supplies vacuum and shuts down the flow of hot water through the heat exchanger. The valve itself is ahead of the HVAC blower plenum near the A/C accumulator. The valve may have been removed and replaced with a manual valve.
The vacuum source is on the other side of the distributor. It's another small line. It connects into a tee with two larger hoses near the brake booster.
thanks its hard to straighten things out after a couple of previous owners hack away on the car then give up and sell it. there is a guy that owns a C3 down the street. I will have to ask him if I can take a look at how his vacuum hoses are connected.
1981 HVAC Problems
