How about a little heater help?

[soba_03]

Ok folks,

It's a 68 C10 307 auto. The heater worked perfectly earlier this year and fan was great, super strong. Now that it MUCH colder it seem that I can't get the blower out of low. It just barely blows. The heater switch is find and the levers and bushings are in tact. I can run a hot wire to the blower motor and it seems like it works perfectly. However when using the blower lever and the standard truck wireing it only blows low.

I suspect that it's the little spring (temp sensor) mounted in the heater duct behind the glove box. I can't think of it's corrct name right now.

Ok what is it's purpose? Can I bypass this "thing" and make the blower work on high and adjust my heat output with the levers? Just wondering. Tired of every night after work getting into a really cold truck and waiting forever for it to blow enough to clear frost and fog off the window.

Yes the coolant level is correct and the thermostat is correct as well.

Any help would be wonderful.

Thanks...

[mrein3]

I think the "spring" thing you are referring to is the resistor block. It drops the voltage to your fan, reducing fan speed. Take a look at the wiring behind the controller. A lot of times the wires melt down. Get a wiring diagram and make sure all the wires work as designed.

[soba_03]

"Resistor" Ok i' assuming you mean the one that mounts in the heater duct?

I have chcked the wireing at the switch and ran all the dash and heater wiring and can't locate a problem. IF the reistor is bad I'm assuming that it could create my problem? Like I said jumper to the blower runs it at full speed. I'll look inot it further.

[brak]

Originally Posted by soba_03

I suspect that it's the little spring (temp sensor) mounted in the heater duct behind the glove box. I can't think of it's corrct name right now.

I would agree. it's most likely the resistor.
it's an easy replacement, only 2 screws (iirc), and it only costs about 10 bucks.

[soba_03]

It my own fault, this summer I R/R the heater core and found that the resistor that was in the truck was bad and I threw in one I had picked up at a yard that was used. I guess that it's time to stick a new one in there and go from there. I just wasn't sure if there was any mods to this in an attempt to eliminate maybe a weak link.

thanks..

[soba_03]

Ok I guess that this thing isn't as easy to find as I thought. tried a few local shops and they looked at me as if I had a third eye.

I did check out Chevy Duty web site for it but didn't locate it through there website. Who has purchased one and from where?

Thanks.

[brak]

I purchased one last winter, either from chevy duty, or GMC paul's.

EDIT--->
the resistor is P/N 363040 ($12) on GMC Pauls website.
it's on the main page of the Heater & A/C section

[chris71]

are you sure that the fan switch is not the problem?i would think that is the problem. if your fan switch goes, you will have no high speed, if your resistor goes you will have no low speed. i had the same problem, no high speed on the fan, replaced the fan switch ($12 from LMC) and problem solved. whatever you do good luck.

[BLACK AND BLUE 67-72]

Problem sounds like the resistor, some parts houses can still get it but they actually have to look for it. I'll see if I can get the 4 Seasons part # for you.

[BLACK AND BLUE 67-72]

FSE #20906 about any halfway intelligent parts guy can cross that number!!

[Kager67]

I agree with chris71. The resistor is there to give you your low fan speeds. Without that your fan would blow on high all the time. I would check your switch. JMO

kage

[sneakysnake]

Check the relay its what controls the high speed.

[67chevemall]

bypass the ford parts and just run it on high or off.

$0.02

[Hutch]

soba_03
Check the ground wire that is on the relay harness behind the glove box.
It is mounted up high
Symtoms on the fan switch are
low = low
med = medium
high = low
The ground wire (black) goes from the relay harness to the firewall and gounds on one of the heater box studs.
You can jump a ground for a test.

[jayharrell]

I'm having the same problem with mine. Do you have a pic of where that ground needs to be on the realy?? It looks like it doesn't have a place or plug, but the wiring diagram looks like it just screws to one of the mounting screws.

[soba_03]

Jay,

Here is what I found on mine. The blower switch would only operate on low. I ordered a resitor however had it fixed before parts arrived. I found that the switch on the heater control wasn't making good contact. So I added a little dielectric grease to the pins and changed out the reistor any way and it works fine. I'm told that for some reason the wireing at the heater control tends to over heat and melt. Mine was fine but that is what I was told. I found that connections were a little dirty and not making good connection so cleaned those up and works good. Actually the ground is actually on one of the heater box mounting studs. Hope you get it worked out. If your flow still remains low and you haven't pulled your fan and heater core out ever. You might consider pulling it out and cleaning out the years of debris that collect in the heater area.. Mine worked fine, had to change out heater core and removed a mouse nest ot two now it will part your hair when it's on defrost..

[jayharrell]

Thanks for the info. It was the ground. I hooked one up from the monting screws on the relay to the firewall and bam-o. Worked exactly right. Thanks for the help