The high fan speed works fine, everything I found said it could be the relay, replaced with delco relay for our 67 Camaro. It is an AC car. Low and medium still not working, I also read could be a ground issue, I tried ground the relay (there is a ground wire to it) but still nothing. Using my test light connected to ground I touched the two prongs that are vertical to each other at the same time and the low and medium work. What could the problem be?
I am not sure on the 67 but on the 69 there is a resistor on top of the AC suitcase pull the connector off and make sure all of your terminals are cleaned and then try it otherwise you may need to replace the resistor. I believe high speed is always hot and the resistor controls low and med.