Heater Fan doesn't blow on low

[Richard]

Originally Posted by HO455

It's also possible the AC fan relay is causing problems.

Here are some threads to help.
First has some good tests for components

https://67-72chevytrucks.com/vboard/...d.php?t=848097

This one is a great discussion on how the AC fan circuit works along with a wiring schematic.

http://67-72chevytrucks.com/vboard/s...d.php?t=813743

And one more.

https://67-72chevytrucks.com/vboard/...d.php?t=731399

A/C fan relay just provides a direct 12v to fan in the high speed mode. Would not cause this, if bad no high speed. I would bet a dollar it is the resistor if nothing obvious at fan switch. 50+ years on a part can cause problems. Just changed the resistor in my friends 67 Chevelle with A/C, same part. All is good now.