Climate Control Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Super_Dave · 05-04-2015, 08:27 PM

I noticed that my Climate Control fan on my '74 is always running... It has a Low-Med-High fan setting, and apparently no way to have the fan completely off. Is this how these trucks were designed or am I missing something?

Titomars · 05-04-2015, 09:34 PM

That's how they are designed. It was called Flow Through Ventilation. In my opinion one of GM's more idiotic ideas.

kalbert · 05-04-2015, 10:01 PM

Some of the later ones have an off position on the blend door lever that will block the outside airflow and shut the fan off. Not sure when that started.

Liberty · 05-05-2015, 06:34 AM

Mine in my 82 doesn't run unless I have the A/C or heat on...

homemade87 · 05-05-2015, 06:53 AM

Also I think it was designed to keep some ventilation in the vehicle in case there was carbon monoxide in the cab while it was closed up and sitting still . There was a lot of vehicles that did this for that purpose . Not just trucks .

Titomars · 05-05-2015, 09:52 AM

Quote:

Originally Posted by homemade87

Also I think it was designed to keep some ventilation in the vehicle in case there was carbon monoxide in the cab while it was closed up and sitting still . There was a lot of vehicles that did this for that purpose . Not just trucks .

I don't know about that. But I do know GM was the only manufacturer to do this and it was on all domestic GM light trucks and cars in the 70's.

motornut · 05-05-2015, 10:42 AM

yup it was the same with no AC.
I cut the low speed bypass(brown wire) @ the switch.
my 78 has 3 speed,79 4 speed,both now have the lowest as an off position.
I have a spare 79 I was going to see if it could wire up to the 78,to give me back the low.

greg64 · 05-05-2015, 02:14 PM

My 77 is low-med-high, no AC. It's a quirky switch because it spends all winter on high, and all summer on low.

enaberif · 05-05-2015, 02:32 PM

Quote:

Originally Posted by motornut

yup it was the same with no AC.
I cut the low speed bypass(brown wire) @ the switch.
my 78 has 3 speed,79 4 speed,both now have the lowest as an off position.
I have a spare 79 I was going to see if it could wire up to the 78,to give me back the low.

With a tiny push button switch and a relay you could make it be permanently off or on. There is more than enough space on the face to do this.

Titomars · 05-05-2015, 03:27 PM

Quote:

Originally Posted by enaberif

With a tiny push button switch and a relay you could make it be permanently off or on. There is more than enough space on the face to do this.

Why not just use a blower switch for an 82 up. The same cab, there can't be too much different in the controls. This is actually what i am going to look into.

enaberif · 05-05-2015, 04:01 PM

Quote:

Originally Posted by Titomars

Why not just use a blower switch for an 82 up. The same cab, there can't be too much different in the controls. This is actually what i am going to look into.

Looks like you may have to go more towards a 1985 and even then it looks like you only have off/med/high.

By putting a small push button switch together you could have your off/low/med/high

motornut · 05-05-2015, 04:34 PM

my 79 can give me "off" and three speeds for the the 78,
prob just switch the wires over in the plug,and the controller
Note the resister coils are different,doubt that matters.

Guilty-by-Design · 05-05-2015, 04:36 PM

my 82 has a 4 position fan switch, the fan is turned on by selecting ac/heat/defrost and is turned off by selecting the off position

Super_Dave · 05-05-2015, 07:33 PM

Quote:

Originally Posted by Guilty-by-Design

my 82 has a 4 position fan switch, the fan is turned on by selecting ac/heat/defrost and is turned off by selecting the off position

You might have something there...

I wonder if I moved the Heat-Defrost lever to OFF if that would affect the fan. I will take a stab at it and see what happens.

Liberty · 05-05-2015, 07:38 PM

Quote:

Originally Posted by Super_Dave

You might have something there...

I wonder if I moved the Heat-Defrost lever to OFF if that would affect the fan. I will take a stab at it and see what happens.

I would think that would do it. My 82 is the same way.

05-04-2015, 08:27 PM	#1
Super_Dave Registered User Join Date: Jul 2014 Location: Sherwood, Oregon Posts: 974	Climate Control Question I noticed that my Climate Control fan on my '74 is always running... It has a Low-Med-High fan setting, and apparently no way to have the fan completely off. Is this how these trucks were designed or am I missing something? __________________ --Project BABA YAGA!... http://67-72chevytrucks.com/vboard/s...d.php?t=655783 --Project BABA YAGA!... http://67-72chevytrucks.com/vboard/s...ghlight=Belair "Life is tough - wear a cup!" "Old Enough to Know Better - Too Young to Resist" "Junk is something you will need three weeks after you throw it away."

05-04-2015, 09:34 PM	#2
Titomars Registered User Join Date: Feb 2015 Location: Santa Rosa, Ca. Posts: 539	Re: Climate Control Question That's how they are designed. It was called Flow Through Ventilation. In my opinion one of GM's more idiotic ideas. __________________ 1977 Chevrolet C/10 Silverado. Step-Side, Factory 454, TH400, 3.73 Posi 12 Bolt. 1975 Chevrolet El Camino. 350, TH400, 3.08 Posi 10 Bolt.

05-04-2015, 10:01 PM	#3
kalbert Registered User Join Date: Jun 2012 Location: Minnesota Posts: 509	Re: Climate Control Question Some of the later ones have an off position on the blend door lever that will block the outside airflow and shut the fan off. Not sure when that started.

05-05-2015, 06:34 AM	#4
Liberty Registered User Join Date: Feb 2015 Location: Bonham, Texas Posts: 241	Re: Climate Control Question Mine in my 82 doesn't run unless I have the A/C or heat on...

05-05-2015, 06:53 AM	#5
homemade87 Registered User Join Date: Apr 2010 Location: Guntersville Alabama Posts: 1,073	Re: Climate Control Question Also I think it was designed to keep some ventilation in the vehicle in case there was carbon monoxide in the cab while it was closed up and sitting still . There was a lot of vehicles that did this for that purpose . Not just trucks .

05-05-2015, 10:42 AM	#7
motornut 78K & 79C Jimmys Join Date: Nov 2009 Location: Ottawa Ont CANADA Posts: 7,901	Re: Climate Control Question yup it was the same with no AC. I cut the low speed bypass(brown wire) @ the switch. my 78 has 3 speed,79 4 speed,both now have the lowest as an off position. I have a spare 79 I was going to see if it could wire up to the 78,to give me back the low. __________________ John 1978 GMCJimmy4X4-350/203 1979 GMCJimmy4X2-305/350

05-05-2015, 02:14 PM	#8
greg64 Registered User Join Date: Dec 2007 Location: Kimberley, BC, Canada Posts: 799	Re: Climate Control Question My 77 is low-med-high, no AC. It's a quirky switch because it spends all winter on high, and all summer on low. __________________ Greg 64 GMC Suburban - 283, NV3500, 14 bolt 77 C10 swb - 292, SM465, 12 bolt

05-05-2015, 04:34 PM	#12
motornut 78K & 79C Jimmys Join Date: Nov 2009 Location: Ottawa Ont CANADA Posts: 7,901	Re: Climate Control Question my 79 can give me "off" and three speeds for the the 78, prob just switch the wires over in the plug,and the controller Note the resister coils are different,doubt that matters. Attached Images __________________ John 1978 GMCJimmy4X4-350/203 1979 GMCJimmy4X2-305/350 Last edited by motornut; 05-05-2015 at 04:44 PM.

05-05-2015, 04:36 PM	#13
Guilty-by-Design Registered User Join Date: Jan 2009 Location: Winfield, Kansas Posts: 54	Re: Climate Control Question my 82 has a 4 position fan switch, the fan is turned on by selecting ac/heat/defrost and is turned off by selecting the off position



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