1979 k20 blower motor

[jdsteph]

Can someone tell me what fuse powers the blower motor on a 79 k20 with air? I am having trouble getting the fan motor working. Is it the fuse for the air? I don’t see one that says heater. The fan will run if I run a jumper directly to the battery. I would assume the ground is good since it runs when I jump it. I replaced the blower motor cutoff relay and the blower motor resistor. I have power going into the cutoff relay via the orange wire but nothing coming out to the motor.

 

[Ricko1966]

Can someone tell me what fuse powers the blower motor on a 79 k20 with air? I am having trouble getting the fan motor working. Is it the fuse for the air? I don’t see one that says heater. The fan will run if I run a jumper directly to the battery. I would assume the ground is good since it runs when I jump it. I replaced the blower motor cutoff relay and the blower motor resistor. I have power going into the cutoff relay via the orange wire but nothing coming out to the motor.

If you have power to the relay and nothing coming out of the relay to the motor I'd assume you are not getting signal or ground to the relay.The relay however only controls high speed the resistor is for lower speed do you have power to the resistor? As for the fuses. Test them all in place with a test light. Key on engine off all accessories on including heater. Ground a test lamp. Touch the metal on each fuse on both sides noting any that don't have power on one or both sides. A good circuit will light the light on both sides,a blown fuse only one side will light,a fuse that won't power the light on either side is a dead circuit. This is a mistake a lot of people make they check the fuse and it's good so they move on. A good fuse on a dead circuit is absolutely useless. Does your fuse box look like this one? On this one fuse B is heater blower.

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[75gmck25]

As Ricko1966 explained, the lower speeds go through the resistor pack and the fuse in the fuse panel, but high speed uses the blower relay, and it’s powered through a separate fuse and power feed. You need to troubleshoot high speed and lower speeds separately.

To troubleshoot high speed you need to put the dash switch on max speed and figure out why the relay does not turn the blower on. For the lower speeds you may need to look at the plug in the back of the dash switch and flow the wiring.

 

[Jgonick]

Dark blue wire at relay will have the power for the lower blower speeds and it will go to the blower by the purple wire. When you switch to high speed, orange wire will power relay to switch from dark blue wire to red wire to to go through the purple wire to blower. See attachment:

 

[jdsteph]

My fuse box does look like the one pictured. Thanks for all the info everyone. I’ll start checking things and get back later.

 

[jdsteph]

Ok. New info. I changed the fuse and the fan works on all speeds, but then blows the fuse again when switching from high back to medium fan. It won’t blow it every time but does it quote frequently but always going from med to high or high to medium. I already have replaced the high speed relay. It sounds like a pop in the switch when it blows. Bad switch maybe????