On my 68 Catalina, the AC fan works on each speed except High. On that setting, the fan stops, and there is a sound of a vacuum leak behind the dash. As I recall, in those days they used a vacuum based control system for HVAC. Dried out vacuum line? Or worse?

 

DP

Vacume was used to move the flappers and control where the air was flowing.  Vents, Floor, defrost, Hot or cold.  Fan/switch is electrical. 

also a 30 amp fuse off the back of the alternator for high fan/a/c. as justa said mechanical or vacuum related. fan speed is justa resistors to slow down the 12v

Thoughts:

I think you guys are right - this is an electric, rather than a vacuum problem.

The fuse off the back of the alternator checks out as good. Without it, there is no fan at all.

Since the blower turns, I don’t think it’s a blower motor problem.

Since I get the low, medium 1 and medium 2 fan speeds, I don’t think it’s a blower motor resistor problem.

Since the AC fan fan relay controls the high fan setting, I’m thinking it’s a fan relay problem.

What do you think?

Could be connection in the switch.  Would have to inspect a replacement (online) to see if it can be taken apart to clean. Or pull yours to check.  Fan Relay is the only other choice.  Putting me on my back under the dash, I would rather sip 90w gear oil. Did I mention I hate electrical????

I’m still willing to get down there - you know, now that I have my Life Alert button to call for help getting up. 😂

Dang...need to get me one of them.

Hey. Quick update on this topic.

I had to order the relay - took forever to get to “Middle of Nowhere Wyoming” - and then I couldn't find time to get back to the project.

Anyway the new relay fixed the problem.

One item off the list. Not sure how many more on that list, but there are a lot of digits.