The General Motors HVAC systems from the 70's through the 90's or so only used a relay for full blower speed. The lower speeds went through the fan switch contacts and a stack of nichrome resistors that hung down into the air stream from the blower to keep the resistance wires cool.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!