How to shut off the heater blower fan?

[Gregski]

I swear as soon as I turn the key the fan in the cab starts blowing and making noise, even when my heater controlls are in the off position.

Any idea what could be causing that and a remedy for it? Please don't say pull the fuse, LOL

(I would share a pic but I don't know how to photograph noise)

74 GMC 1/2 ton, V8, manual, no AC

[tucsonjwt]

The fan is always on at very low speed because of GM's "flow thru ventilation" design in this era of vehicles. I think if you search this forum you can find some info on interrupting the power to the fan switch with a separate toggle switch and turning it back on when you need it. This feature never bothered me, but I think you may have a noisy blower motor which needs replacing - cheap and easy fix.

[homemade87]

It was a safety feature to keep carbon monoxide (ventilation) out of the cab. By design it always stays on. If you can here it running you must have noisy one. I never notice mine.

[Gregski]

Originally Posted by tucsonjwt

The fan is always on at very low speed because of GM's "flow thru ventilation" design in this era of vehicles.

Thank you, I went back and read the Service Manual, and later found it also in the Owner's and Driver's Manual (page 33).

Chapter 1A HEATER AND AIR CONDITIONING (funny how the chapters you skip always come back to make a fool out of you) page 1A-4

Fan Control

The blower fan lever is located at the left hand side of the control assembly. The blower motor will operate as soon as the ignition switch is turned to the RUN position. The control has three positions only; LO, MED, HI. There is no OFF position.

Oh well, one less thing to "fix".

[Monty]

there is a resistor bank on the heater box under the hood with a wire plug connecting to it. you can unplug the wire connector and bend one of the tabs flat so it doesn't go into the connector when you plug it in. I do not remember which tab it is right now though.

this 'mod' is reversible.

[rich weyand]

As Monty says, you can bend the tab on the blower resistor connector on the firewall. This will turn the LOW position into an OFF position. You will then have MED and HI, but no LOW speed. The tab you bend is the one that connects to the brown wire on the connector.

You can also intercept the brown wire that provides power to the blower motor control on the dashbboard. Remove the dash bezel, and then remove the connector to the blower motor control. One of the positions on that connector has two brown wires in the same position. One joins with the other two wires from the blower motor control to go to the blower motor resistor, the other goes to the fusebox. Cut the one going to the fusebox, and insert a switch there. You will then have a way of turning off all blower speeds. When that switch is on, you will have all three speeds available.

There is also a connector where that brown wire to the fusebox joins the wiring harness, about six inches back along the wire from the blower motor control. You may be able to disconnect that and connect your switch in to the circuit with a couple spade connectors. I can't get that connector apart on mine no matter what I try.

[Oregoon]

Seems a common problem, my friend: http://www.67-72chevytrucks.com/vboa...d.php?t=650509

Big thanks to Rich for outlining the (optional) fix.