Heater

[Frogurt]

Hello,

I have a 69 C-10, I pushed the lever over to turn the fan on for the heater and nothing. I have left on and as just driving it came on, I did not need at the time so turned it off. Now when I need it I turned on and nothing doesn't work again. Anyone have any ideas what would cause this to happen? It has done this a couple times now. I have checked the fuses, ground. Has new blower motor also new fan about 2 years ago, truck doesn't really get driven that often to use the heater.

Thank you for your help.

[Accelo]

Electrical issues are difficult. Sometimes one will get lucky and come across a very common issue that can be easily resolved. Will attempt to help. You will need some tools, at the very least a 12V test light. Throwing parts at an electrical issue is one method to go broke. Start by jumping the fan to the battery and confirm it runs. New doesn't mean it works. Report back and someone will jump in. Confirm it is or isn't an Air-Conditioning truck.
Cheers.

[pjmoreland]

The fan normally has multiple speed settings, depending on how far over you push the lever. The lower speeds run the power through resistor windings that are mounted in the heater box. The resistors could be bad or failing. Even so, high speed should still work. Does the fan come on if you push the lever absolutely all the way to the right?

[Frogurt]

It is a non a/c truck. This morning checked the fuse it appeared to be blown replaced the fuse and it instantly blew, tried 2 differnet ones. The one that came out appeared to say 3 AG on it. I had tried a 5 that is what was blowing. I will have to try and look at more tonight or the weekend when have more time to dig into things.

Thanks again for the help.

[michael bustamante]

if youre blowing fuses there might be a short in the motor itself of resistance built up in the squirrel cage.. pull it out and clean it and test with a multimeter... Im sure someone here knws the correct ohms for it

[Wrenchbender Ret]

3 or 5 amp fuses are way to light for a heater. It probably takes a 10 amp for one without A/C. 15 amp would work better. Sometimes the motor has a little drag getting started when older.

George

[Accelo]

The correct amperage, for each location, is engraved on the fuse block.

[HO455]

The heater /AC fuse can be confusing due to way GM labeled the fuse. It is the top left fuse on this fuse block. Non AC trucks use a 10 amp fuse and AC trucks use a 25 amp fuse. See photo. Heater only circled in red. AC circled in blue. The 3 amp fuse below is for the radio.

[72SB]

^^, your fuse looks to be a 25 amp, AC Truck, right?

[HO455]

Actually I found that photo here. Thanks, John! Member #16!

http://67-72chevytrucks.com/vboard/s...d.php?t=400597

As far as my truck I have installed an AC blower motor and its wiring in my non-AC truck. This gives me a relay to control the fan speed preventing damage to the factory switch, from too much current, like the factory did.
So I am running a 20 amp fuse based on the current draw I measured. If your interested here's a link to what I did. Scroll to post 871.
The results of the blower swap are on the next page post #876.

http://67-72chevytrucks.com/vboard/s...698377&page=35

[Frogurt]

Update....I have finally had some time to work on this. I have replaced the reisiter and it still blows fuse. I have cleaned all of the grounds. When I have the truck in Accessoy or ON position the fan blows and works great. As soon as I start the truck in about 10 seconds the fuse blows. What other steps can I take to trouble shoot this issue?
Thanks again for the help.

[Frogurt]

Another update.... I have now replaced the blower, resistor as well as the switch and I still can only run on low or medium without blowing a fuse. As soon as I put it to high it blows the fuse in about 1-2 seconds. Can someone please give me others things to try to resolve this issue. Greatly appreciate any help.

Thank you

[Thealien]

Blower motor or short circuit?

[HO455]

It may be that you are having a voltage drop somewhere in the circuit. That can cause a fuse to blow. It's not uncommon to have a poor connection on the back side of the fuse block.

I made a little drawing to help you check the voltages in the circuit. You can start at the ignition switch or the blower motor then work your way along. Checking each end of the fuse can show it you have a bad fuse holder.

Here is a link to the wiring diagrams for our trucks.

https://67-72chevytrucks.com/vboard/...d.php?t=185856

Good luck and let us know what you find.

[dmjlambert]

What size fuse do you have in it when the fuse blows?

[body bolt]

Originally Posted by Frogurt

Hello,
I have left on and as just driving it came on.

Perhaps there are leaves or a rodent nest in the heater box and driving knocked it enough to let the blower run?

[Frogurt]

Originally Posted by HO455

It may be that you are having a voltage drop somewhere in the circuit. That can cause a fuse to blow. It's not uncommon to have a poor connection on the back side of the fuse block.

I made a little drawing to help you check the voltages in the circuit. You can start at the ignition switch or the blower motor then work your way along. Checking each end of the fuse can show it you have a bad fuse holder.

Here is a link to the wiring diagrams for our trucks.

https://67-72chevytrucks.com/vboard/...d.php?t=185856

Good luck and let us know what you find.

Thank you, I will give that a try

[Frogurt]

Originally Posted by dmjlambert

What size fuse do you have in it when the fuse blows?

Fuse size is a 10 that keeps blowing

[pjmoreland]

I believe all aftermarket blower motors are the higher-rated A/C version. According to the following thread, the A/C blower motor is rated at 16.5A. If this is the case, then a 10A fuse won't work.

https://www.67-72chevytrucks.com/vbo...ad.php?t=76855

[HO455]

That's a good point. Last year when I did my blower motor upgrade from non-ac to ac not many vendors listed both versions. I did find that NAPA listed two separate part numbers.

[Frogurt]

That would explain why it keeps blowing the 10a fuse. Would you recommend going with a 20a fuse then? Thank you for your help.

[pjmoreland]

One concern about running a 20A fuse is that the switch might not be happy with the higher current. A/C trucks have a relay for the blower to take the load off the switch. Hopefully someone who has installed an A/C blower on a non-A/C truck will chime in on whether the switch was able to power the blower directly.

Where did you get your blower, and what is the part number? It would be good to confirm that it is actually an A/C blower.

[Frogurt]

Originally Posted by pjmoreland

One concern about running a 20A fuse is that the switch might not be happy with the higher current. A/C trucks have a relay for the blower to take the load off the switch. Hopefully someone who has installed an A/C blower on a non-A/C truck will chime in on whether the switch was able to power the blower directly.

Where did you get your blower, and what is the part number? It would be good to confirm that it is actually an A/C blower.

I got it from O'Reilly it is a Murray climate control blower motor Part Number PM 102 detail description says Heater / Air Conditioner Blower Motor

[HO455]

Originally Posted by pjmoreland

One concern about running a 20A fuse is that the switch might not be happy with the higher current. A/C trucks have a relay for the blower to take the load off the switch. Hopefully someone who has installed an A/C blower on a non-A/C truck will chime in on whether the switch was able to power the blower directly.

Where did you get your blower, and what is the part number? It would be good to confirm that it is actually an A/C blower.

I don't have an apples to apples comparison to relate (They are both GM's from the same era.) but the experience it spured me on to do the research and then wire a relay in the circuit like a AC truck has when I replaced the old dying blower motor with a new AC blower motor in my Burban.
Anyway years ago I put an AC blower motor and fan from a 70's Firebird in my non-AC GTO. It was my daily driver at the time and after about 18 months the switch began to fail. I pulled the switch apart and the high speed contacts were eroded away. I repaired them with solder which got me through another winter before failing again by then I had found a spare switch to replace it with which worked until I quit driving it everyday.

So I believe the factory switches will work fine unless the truck is being used as a daily driver in the winter. Another thing I have noticed that would contribute to switch failure is before with the old blower motor I never adjusted the fan speed. It was left in high all winter and then it was shut off come spring. Now with the higher output of the AC blower motor I find myself adjusting the fan speed a lot more depending on the weather. The high speed is noisier than before and unless it's cold or I need lots of defroster action I run in medium. If I hadn't wired a relay in every time I switch the fan to high I believe it would be slowing arcing the switch contacts away. All of this is my own theory and opinion.

[Frogurt]

Originally Posted by Frogurt

Another update.... I have now replaced the blower, resistor as well as the switch and I still can only run on low or medium without blowing a fuse. As soon as I put it to high it blows the fuse in about 1-2 seconds. Can someone please give me others things to try to resolve this issue. Greatly appreciate any help.

Thank you

I forgot to say, when I don't have the truck running and it is just on accessory it will work on high forever but as soon as I start the truck it blows the fuse.