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It’s late, I haven’t taken the time to search the forum on this yet, but wanted to get the question out.
1980 L48 rebuilding the AC (and a lot of other parts too)
The blower appears to hit all of its speeds when in “heat”, or vent, or defrost, but doesn’t appear to change speeds when in either AC setting. AC compressor was cycling, so AC was “on”. Anyone run into that before? Why would it work for one, but not the other?
Again, I haven’t searched for an answer yet, but wanted to get question out. I also need to get back to the car tomorrow and try the options again. With a lot going on, perhaps it was working and I was mistaken.
Yes I have. The lever that you slide for heat/ A/C / vent. Does 2 things under your console. One it moves the vacuum switch that controls the doors that move to direct air up middle or down, and on the other side is a electrical switch that directs power to the blower switch and to the compressor clutch.
looks like this.
Now under that metal strap over the center of the round part of the switch is a plastic rivet that let's go with age just like the one on the vacuum switch.
here's mine.
When this let go, the switch "tipped" on a angle allowing electrical connections in some areas but not all. Exactly like your car now.
so I repaired the switch the same way we all repair the vacuum switch which suffers from the same broken plastic rivet problem. Except, due to clearance I had to counter sink the nut on the far side by melting it into the plastic. Not hard but great care is needed to not melt to far or to much.
Looking like this.
Was a real "putzy" project. Cost zero cents and my blower control is perfect again.
This is a new module on mine, I broke the little tab that secures the heater door cable on the original getting the clip unhooked. I would have hoped a brand new one wouldn't have had some of these same "old" issues.
When testing this switch, keep in mind the reason for this switch is, in factory form. On Max Air, the fan blows on maximum. In normal AC, complete fan speed control returns. (This is easy to wire around and many do).
Starting in 1979 GM changed the Function Control Switch eliminating Circuit 988 (1977) or 52 (1978) from it so all fan speeds were available even in MAX A/C mode.
To get full fan speeds on the 77 or 78 you simply remove the double orange wire from Cell #2 of the function control switch connector.
You must then insulate the now exposed terminal of the double orange wire.
A couple electrical insulators would be electrical tape or a couple layers of heat-shrink tubing around the terminal end...
Last edited by bmotojoe; Oct 15, 2023 at 07:48 AM.
I ran into the same thing when I rebuilt the entire hvac system on my 79. After I put in a new heater ac control assembly in the center console things weren’t working correctly, each mode would work but fan speed was stuck on low. I found all it was is that the detents in the selector weren’t quite right. All I did was move the selector a few millimeters left or right of the detent and I got fan speed to work properly, it’s a very minor annoyance that I’ve just learned to live with. All good info above but it might be as simple as what I dealt with. Maybe it will save you from tearing things apart again.
I ran into the same thing when I rebuilt the entire hvac system on my 79. After I put in a new heater ac control assembly in the center console things weren’t working correctly, each mode would work but fan speed was stuck on low. I found all it was is that the detents in the selector weren’t quite right. All I did was move the selector a few millimeters left or right of the detent and I got fan speed to work properly, it’s a very minor annoyance that I’ve just learned to live with. All good info above but it might be as simple as what I dealt with. Maybe it will save you from tearing things apart again.
Gralls, I had a few minutes tonight to mess around with it and what you pointed out is exactly what I am experiencing. If I slide it a little off the actual detent, the fan speeds work as expected. As you said, a minor annoyance. I have my old unit sitting around, so perhaps I'll check it out to see if there's some way to adjust before I dive back into the just finished console.
All in hindsight, there are a few things I wish I would have bench tested a bit before I closed things up in the car. Just in a rush to get it all pinned back together and I should have tested a few points out first beforehand. Again, hindsight, lesson learned!
Starting in 1979 GM changed the Function Control Switch eliminating Circuit 988 (1977) or 52 (1978) from it so all fan speeds were available even in MAX A/C mode.
That sounds right to me. In my '79, all four blower speeds function the same in MAX A/C as they do in other modes, such as NORM A/C, And I prefer it that way.
I ran into the same thing when I rebuilt the entire hvac system on my 79. After I put in a new heater ac control assembly in the center console things weren’t working correctly, each mode would work but fan speed was stuck on low. I found all it was is that the detents in the selector weren’t quite right. All I did was move the selector a few millimeters left or right of the detent and I got fan speed to work properly, it’s a very minor annoyance that I’ve just learned to live with. All good info above but it might be as simple as what I dealt with. Maybe it will save you from tearing things apart again.
I had exactly the same problem, and settled on exactly the same solution. I would prefer that everything on the car worked exactly as it was designed to, but I have resigned myself to the fact that 40+ year old cars have a few 'idiosyncracies'.
Blower speed not working during AC
