Blower only works on one speed

[ScottH]

Been having problems with the blower motor working in my 72 C20 w/ac.
Got it working today but it only works on one speed (low).

Could it be the switch or I noticed in a wiring diagram there is a resistor. If resistor can anyone tell me where and what to look for?

Any help or suggestions are appreciated.

Thanks.

[POS72K10]

Dont know about the resistor but I had the same problem! I got mine to run on high by following the cable from the fan speed switch to the lever under the passenger side of dash and moved the lever with my hand till the fan kicked on high and havent moved it since. (temp fix) Hope this helps.


but hey it works!

[cheyenne10]

Most likely the fan relay located on passenger side of cardboard glove box insert. I took out my glovebox to do the R/R. Seemed like a real pain. Fixed problem though. I also have heard of bad grounds on the system to cause this. Relay should be $10-$15 from most board vendors. Its a tight area to get to.

[ScottH]

Thanks guys, I should have mentioned that I've already replaced the blower motor relay.

Any other ideas? Guess I may have to go for a new switch.

Happy holidays to all!

[67chevytrk]

I had this problem with my 67, it turned out only one leg of my resistor was working properly.

The heater resistor can be found behind your glove compartment, just open you glove compartment and take out your glove compartment totally and you will see your resistor sitting on top of your heat/air plenum.

I know Classic Industries carries them for our trucks, just go here:

http://www.parts123.com/PartFrame.as...sic_Industries

Go to the top left where it says search by item description and hit the down arrow to the right of it and select (Search by) Part # and right underneath that type: G5094

You may also check your local autopart store. They are easy to replace, if they are old they build up some rust and should be replaced anyways.

If it's not that then I would go for your switch, Hope this helps.

[67chevytrk]

68-75 Blower Motor Resistor Original GM w/ Acc AC Pickup G5094 14.95 Each Info

This is what you get when you do a search for search by item description and you type in heater resistor and select year '72 and hit search

[BOSS]

could this also be the cause of mine not working on high,i get low and medium but nothing on high

[aggiedave98]

High does not use the resistor pack. The lower speeds all use the resistor pack... adding more resistors in series to lower the voltage and lower the fan speed.

That's in general. In my '89 Suburban it then works this way... probably the same for you...

The relay switches between using the voltage that comes out of the resistor pack (low/med) and the voltage coming from the battery (12V) for high.

hope that helps...

[Longhorn Man]

Originally Posted by BOSS

could this also be the cause of mine not working on high,i get low and medium but nothing on high

Boss, do you have A/C on your rig? If so, I would look at the high speed fan relay found only on A/C trucks.