72 A/C,heat,defrost blower stopped working?

[cherokeejohn]

So on my 72 350/th350 factory A/C truck, the blower just stopped working this past week. About a month back, I took my diverter box out, cleaned and greased it, replaced gaskets, cleaned all vents and ducts, and reinstalled it. The blower worked before this, and after it as well. This past week, we had our first frost here in the Mid-Atlantic area. i went out, started her up, turned the defrost on, turned the fan on high and let her warm up. come out just shy of 10 mins later and it had only defrosted a area the size of a baseball. i felt the defrost vents and i can feel heat, just no force behind it, flipped the fan switch a few times, i can hear a noise coming from behind the diverter box or the glovebox (cant determine exactly where. but i can hear it trying to do something. I've researched a bit on it and it is between the fan switch, the blower motor, or a resistor . any help or info on this would be great if anyone else has experienced this problem or similar. I don't want to just start buying a buncha parts and spending un-necessary money chasing a gremlin. this truck is my DD and WINTER IS COMING FAST. defrost is a must have.

[howzzzit]

Check out this thread.

https://67-72chevytrucks.com/vboard/...d.php?t=848332

You didn't say if air blows anywhere else?

[MARKDTN]

There is also a fan speed relay that can cause issues but with it you usually have high speed only. I would start with a good multimeter and see what voltage you have at the fan in various speeds. For high you should have battery voltage and the lower speeds progressively less of course. I would make sure I had a good ground to the fan motor. That would give you a place to start.

[71CHEVYSHORTBED402]

Originally Posted by MARKDTN

There is also a fan speed relay that can cause issues but with it you usually have high speed only. I would start with a good multimeter and see what voltage you have at the fan in various speeds. For high you should have battery voltage and the lower speeds progressively less of course. I would make sure I had a good ground to the fan motor. That would give you a place to start.

That's real good. Perhaps ground came loose during the assembly of parts.

Hopefully the blower is good, it's a (*&^^) to replace. At least on my 402 A/C it is.

[cherokeejohn]

thanks to all of you for the info. pulled the whole HVAC control panel out, laid it on the console this afternoon, and reached for my test light and suddenly the fan kicked on. upon closer inspection i noticed the wires an plug to fan switch were a bit crunchy/burnt crispy. guess ill be playing "custom auto electrician" this weekend. in meantime, my brother tossed me a auxiliary12V defroster from his skid loader, so if we get any frosty mornings before i fix the fan wiring, i wont be driving down the road looking like Ace Ventura with my head out the window,

[71CHEVYSHORTBED402]

Originally Posted by cherokeejohn

thanks to all of you for the info. pulled the whole HVAC control panel out, laid it on the console this afternoon, and reached for my test light and suddenly the fan kicked on. upon closer inspection i noticed the wires an plug to fan switch were a bit crunchy/burnt crispy. guess ill be playing "custom auto electrician" this weekend. in meantime, my brother tossed me a auxiliary12V defroster from his skid loader, so if we get any frosty mornings before i fix the fan wiring, i wont be driving down the road looking like Ace Ventura with my head out the window,

This seems very common. Who knew 50+ years could do that to a fan switch's wiring