Blower only works on one speed - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**ScottH** · 12-23-2005, 10:57 PM

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 · 12-24-2005, 01:52 AM

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 · 12-24-2005, 02:07 AM

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** · 12-24-2005, 09:43 AM

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 · 12-24-2005, 10:38 AM

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 · 12-24-2005, 10:50 AM

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** · 12-24-2005, 11:06 AM

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

Longhorn Man · 01-10-2006, 12:01 AM

Quote:

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.

aggiedave98 · 01-09-2006, 11:39 PM

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...

12-23-2005, 10:57 PM	#1
ScottH Senior Member Join Date: Sep 2002 Location: Hampstead, NC Posts: 8,190	Blower only works on one speed 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. Last edited by ScottH; 12-23-2005 at 10:58 PM.

12-24-2005, 01:52 AM	#2
POS72K10 Registered User Join Date: Dec 2005 Location: Box Elder S.D. Posts: 22	Re: Blower only works on one speed 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!

12-24-2005, 02:07 AM	#3
cheyenne10 Senior Member Join Date: Apr 2000 Location: Oregon Posts: 2,512	Re: Blower only works on one speed 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. __________________ Bob

12-24-2005, 09:43 AM	#4
ScottH Senior Member Join Date: Sep 2002 Location: Hampstead, NC Posts: 8,190	Re: Blower only works on one speed 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!

12-24-2005, 10:38 AM	#5
67chevytrk Damn I'm broke Join Date: Nov 2005 Location: Roanoke Texas Posts: 49	Re: Blower only works on one speed 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. Attached Images __________________ [B]67 Chevy truck stepside small back window 96 Dodge Indyram 74 Dart Sport 96 Neon

12-24-2005, 10:50 AM	#6
67chevytrk Damn I'm broke Join Date: Nov 2005 Location: Roanoke Texas Posts: 49	Re: Blower only works on one speed 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 __________________ [B]67 Chevy truck stepside small back window 96 Dodge Indyram 74 Dart Sport 96 Neon

12-24-2005, 11:06 AM	#7
BOSS Just here to help Join Date: Jan 2002 Location: Norwood,Mo Posts: 3,890	Re: Blower only works on one speed could this also be the cause of mine not working on high,i get low and medium but nothing on high __________________ Support our site Norwood Survivor

01-09-2006, 11:39 PM	#9
aggiedave98 Senior Member Join Date: Aug 2003 Location: Sugar Land, TX Posts: 1,007	Re: Blower only works on one speed 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...



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.