Ok, I'm really frustrated at this point. I just tried replacing the blower a/c switch with a NOS one and the fan still runs on high. It's hard to get the old switch out so I just unplugged it and tried the new switch and nothing changed.
It really looks like the fan is hard wired to high but I had someone look at it and he said no. How can I troubleshoot this? I'm thinking the fan must be hard wired on high and the blower switch is being bypassed.
Take a look at these, it is for 1977 but they may help. Going off memory the Air Inlet Valve Switch will run the fan in High. 65 is high, 63 the lowest speed, etc... The small relay at the bottom is to delay the AC for a bit after starting the engine. Brian
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Forum member DadHad1 lives local to me and helped troubleshoot and resolve this issue. After trying to replace both the blower resister and the fan switch Mike determined the issue to be the "air inlet valve switch" located under the right side of the dash. We unplugged it and now all 4 fan speeds work properly. Does anyone know if this can be left unplugged or what this part does? I took a picture of it.
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From my understanding if the upper lever (AC Max or Norm) is in the Max position the air inlet valve switch should be made so the fan runs on High regardless of the fan switch position. Depending if the operator for the air inlet valve switch is vacuum open or vacuum closed (I think it should be vacuum closed, switch made but I'm not sure) then you might have a vacuum issue or a stuck air inlet valve operator or stuck switch. Just what you wanted to hear.
For every position the air source is outside except when the AC is in Max. Hopefully it is simple but I would want the AIV open unless you are running the AC on a super hot day.
I think I solved the issue. The vent was stuck partially open which was causing the air inlet valve to be stuck. Once I freed the stuck diaphragm lever assembly my fan works!
IMG_20141004_110400678.jpg
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