74 C10 Blower Switch

[Bandit130]

74 C10 350/TH350 w/AC. The blower motor switch has 4 speeds, but no off. Fan runs all the time on lowest speed. If my memory serves me right, this is what GM called "flow through ventilation". I'm not a fan of this. Is there a way to disconnect the low speed where it would then become off and the other 3 speeds work?

TIA

[Jeramy]

on my 81 fan shuts off when you put mode selector in off position

[chrismoore701]

I heard the older trucks had the fan always run on low to help evacuate the exhaust fumes from the cab

[Bandit130]

Originally Posted by Jeramy

on my 81 fan shuts off when you put mode selector in off position

I have done that and fan still blows coming thru the ac vents. I have been setting it on heater and cold or defrost and cold. Still blows thru defrost vents. Just have not found a way to completely shut it off yet.

[tucsonjwt]

My 73, 76, and current 83 all had constant low speed fan on due to "flow thru ventilation."

If you search this forum you will find some who have disabled the constant fan on wire, or just disabled low speed altogether.

I have never considered it to be a problem, but I live in the usually too hot desert.

[TrailerTrash]

Im pretty sure there is a wire that can be snipped on the switch plug that will disable the constant on and actually make the lowest position the off position.

im sure someone will chime in with more info

[motornut]

i clip the jumper wire at the switch,78 shown
my 78 non AC is three speed,<- winter truck
my 79 non AC is four speed, ,<- summer truck
both low speeds clipped.
But I'm going to switch in a 79 4 speed into the 78 (= 3 speeds plus off)

[Bandit130]

Originally Posted by motornut

i clip the jumper wire at the switch,78 shown
my 78 non AC is three speed,<- winter truck
my 79 non AC is four speed, ,<- summer truck
both low speeds clipped.
But I'm going to switch in a 79 4 speed into the 78 (= 3 speeds plus off)

Thanks for the info. The pic is a little fuzzy. Is that a brown wire in the connector that you clipped? I have one connector w/4 wires and one w/1 wire on back of switch.

[motornut]

Originally Posted by Bandit130

Thanks for the info. The pic is a little fuzzy. Is that a brown wire in the connector that you clipped? I have one connector w/4 wires and one w/1 wire on back of switch.

yes its brown

[cadillac_al]

74 and 78 both have the brown wire that needs to be clipped to disable low? I'm not a fan either.

[motornut]

Originally Posted by cadillac_al

74 and 78 both have the brown wire that needs to be clipped to disable low? I'm not a fan either.

in the 78 and 79 it was brown,but it was obvious the small loop was the jumper

[Bandit130]

Thanks to all who have replied to this subject. I decided to perform an experiment to see if by removing wires, one at a time, from the switch connector and testing each fan speed position as to what would happen. The switch has 2 connectors. 1 4wire (brown, blue, green, orange). and 1 1wire (orange). The switch, as a lot of you know, is a vertical switch with 4 speeds. Low, Med1, Med2, High, position from bottom to top. Removed 1 wire at a time, tested, reinstall wire and removed another wire, tested, etc.

This is the results,

Removed Brown wire-fan speed-L,L,L,L

Removed Blue wire- fan speed-L,M1,L,H

Removed Green wire-fan speed-L,L,M2,H

Removed Orange wire-fan speed-L,M1,M2,L

This apparently cannot be done by the removal of any one wire from connector or cutting (clipping) wires, to disable low fan.

Any combination removal results in a Low fan at all or any combination thereof.

I am ready to believe that it may not be able to be done or by having no fan at all at any speed. Oh well, I guess I can live with it after all cause that was enough work as it was.

As for the 1 wire connector, it appears to go to the climate control, possibly for the AC so when using AC the Low setting turns off compressor. That is my conclusion of the single wire.

Any other suggestions would be appreciated.

[motornut]

Can you get a picture?
See if we can figure this in the am?