Heater Fuse Blowing - Team Camaro Tech
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post #1 of 16 (permalink) Old Dec 29th, 17, 09:28 AM Thread Starter
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Heater Fuse Blowing

Hey guys. I signed up in GTOforum.com to ask this question but have no responses. I guess I haven't earned their trust and loyalty to jump in and help. I understand that.

Still working on my friends '67 GTO ragtop.

He has no heat in the cabin. To better define that the 20A heater fuse blows when you turn on the heat. I disconnected the blower motor and AC compressor and the fuse blows. I imagine the circuitry in this car is similar to our Camaros.

I figured I need to trace the wiring from fuse box to the climate control switches and beyond. Any tips from the gang? Any known weak points to focus on?

Secondly the horn does not work. I'll begin by ensuring they work by spanning a wire direct from the battery to each horn, but unlike our Camaros they are difficult to access.

Skunk Works
302DZ, M22W Muncie, GV overdrive,12-Bolt Rear 3.73
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post #2 of 16 (permalink) Old Dec 29th, 17, 09:55 AM
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Re: Heater Fuse Blowing

Use same approach for the heater motor but put a 50 Amp in line fuse in the power feed. If motor runs on high as expected the problem is a short (pinched wire, or one rubbing against sheet metal without a proper grommet to protect the insulation) in the car's wiring.

I use Bussman circuit breakers to prevent having to constantly replace blown fuses.

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post #3 of 16 (permalink) Old Dec 29th, 17, 10:06 AM
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Re: Heater Fuse Blowing

Agree with Dave, and Yes, circuitry is basically the same.
You might unplug the ballast resistor and select HI speed for blower.
The only electrical items are the blower motor and compressor clutch.

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post #4 of 16 (permalink) Old Dec 29th, 17, 10:29 AM Thread Starter
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Re: Heater Fuse Blowing

Thank you Dave and Everett. I straight wired the fan and determined it works. That was after I removed the cursed fan to remove the dried up sealant from the squirrel cage.

The AC ductwork blocking access is now removed. The aftermarket radio wiring looks like a rat nest. The radio will be removed for access and the wiring tidied up when reinstalled.

I'll find that ballast resister and check it out then look for that elusive pinched wire.

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post #5 of 16 (permalink) Old Dec 29th, 17, 03:21 PM
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Re: Heater Fuse Blowing

If you are using a digital multimeter, it should have a 'beeper' in one of the OHMS position and works when leads are touched together out of circuit.
You can hook one lead to ground and the other lead to disconnected fan motor lead with fan speed on HIGH.
If beeping, then short is on power lead. While beeping, you can find the short to ground.
Another tip is measure resistance of power lead from fuse to motor lead in HIGH position.
More than likely, you will be using lead extensions and you can calibrate the extensions by holding the leads together and let the meter 'zero' itself, then connect leads to length of power wire.
Total resistance I would think should be less than an ohm, but, remember how many times high speed has been selected in its life as carbon resistance from sparking every time contacts come close to each other, may have built up on switch contacts giving more resistance for current, thus higher current draw and blows 20A fuse.

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post #6 of 16 (permalink) Old Dec 31st, 17, 07:51 AM Thread Starter
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Re: Heater Fuse Blowing

I do have a nice Fluke multimeter but have to admit I am a rookie with its usage. Voltages and continuity I am okay with but the elaborate stuff I am not.

"You can hook one lead to ground and the other lead to disconnected fan motor lead with fan speed on HIGH.
If beeping, then short is on power lead. While beeping, you can find the short to ground."

I get no beep here. I now have the radio out of the way and will also remove the ashtray assembly. I downloaded the wiring diagram and will get to work tracing the wires from fuse through the system. Hopefully I will find an obviously pinched wire or something. Is it possible the problem is inside the switches?

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post #7 of 16 (permalink) Old Dec 31st, 17, 11:56 AM
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Re: Heater Fuse Blowing

When you hot-wired the fan motor, there was no fuse?
Motor may be toast in drawing too much current even though it does turn.
If looking at the fan motor circuit, fuse, switch, and motor, with appropriate ground connection, are the only items.
As I was suggesting, hold leads together of the Fluke in the lowest ohm range, and watch the meter zero itself, it may end up with 0.1 ohm showing.
Now, connect one lead to fuse socket, the other lead to disconnected power lead at fan, and see what meter indicates.
I believe you may have to add extensions to leads making the distance and with extensions on meter leads, zero the meter and meter will take into consideration the extra length added.
Now you can get a more correct reading of ohm value from fuse socket through switch contacts to motor power spade at motor.
This test would show extra resistance between switch contacts as extra current is drawn and given up as heat - resistance makes heat when current goes through it and this heat is lost power.
Same with ground at motor, has to have a good connection, just like the lights. High resistance at this junction, more power through fuse than needed.
The only problem with Flukes, is max current to measure is 10 AMPS.
GM used the same color through the product lines.

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post #8 of 16 (permalink) Old Jan 1st, 18, 11:40 AM Thread Starter
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Re: Heater Fuse Blowing

When I directly wired the motor to test it I used no fuse in the wiring. I rule it out because I still blow the 20A fuse with it unplugged.

Okay I did the test as described above:

.1 Ohm with Fluke meter leads touching
.5 Ohm from fuse (with wire extension) to ground on engine
400 Ohm from fuse (with wire extension) to disconnected fan connector plug

Sooooo..... What does this tell me?

It tells anyone reading this that I don't know what I am doing. But that is okay, as I want to learn and maybe someone else will be helped by reading this.

Skunk Works
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post #9 of 16 (permalink) Old Jan 1st, 18, 01:53 PM
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Re: Heater Fuse Blowing

I'm going to throw out some questions and some info and hopefully it might help.

First off, do you have a quality picture or wiring diagram of the system ?. I looked around and there is hardly any info out there for this but it might help with troubleshooting.

The next question I have is the below portion of this picture look like the fuse block in your car ?. Again, there isn't a lot of info out there but the description of the fuse block I copied says it is for a 64-72 GTO.



A third question I have is on the fuse blocks, there are normally accessory taps (1/4" male terminals) in the fuse block and on yours, do you have anything plugged into those taps ?. I have them labeled as Optional Accessory.

Jim

1974 Spirit Of America Nova (being restored), 1973 Nova Custom, 1968 Chevy II (Garage Find 2012)

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post #10 of 16 (permalink) Old Jan 1st, 18, 02:21 PM
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Re: Heater Fuse Blowing

Thank you, Jim, for the fuse panel.
So, Andrew, with 0.5 ohm to ground, and using Jim's fuse panel for reference, disconnect coil + power lead and measure again.
Could be measuring through closed point set through coil primary winding to ground.
If not, then as Jim suggests, another circuit tied in ign power is grounded _ Good luck !!!
On 400 ohms, you might disconnect fan switch and re-measure both wires on fan switch plug.
Fan switch power lead from switch connector to fuse, and fan switch connector to fan motor lead.
If both are lower ohms, then fault is in switch contacts being carboned up - use emery paper to clean contacts of switc, or wire across connector making fan work.
Watch fuse, if no blow, then faulty switch, if fuse blows then faulty fan motor.

Heck of a job to do on New Year's Day, be sure in eating your black-eyed peas for good luck - southern tradition, I am.

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post #11 of 16 (permalink) Old Jan 1st, 18, 04:11 PM
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Re: Heater Fuse Blowing

Quote:
Originally Posted by Everett#2390 View Post
Thank you, Jim, for the fuse panel.
I'm just hoping it's a correct picture. I know what the fuse blocks on my car's look like but never had a 67 GTO and then I wonder, has the original been changed out to an aftermarket one or what.

This is why I asked the questions I did. Hopefully the issue(s) can be resolved.

Jim

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post #12 of 16 (permalink) Old Jan 1st, 18, 04:59 PM Thread Starter
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Re: Heater Fuse Blowing

The fuse panel in this GTO has the 2nd position on LH side as the heater fuse. It looks similar to what is posted above but not exact. I've found and printed some wiring diagrams. There are a couple of wires connected to the accessory taps.

However this is what I figured out today:

I was tracing the under dash wiring and figured I should check the two plugs that connect to the climate slide switches. I unplugged them, including one that I could see the butt end, but not the connection. With them unplugged the fuse did not blow. Is this true, lets try again. Sure 'nuf no fuse blowing. I plugged one connector in and the fuse held. I plugged in the other and the fuse held. What's going on here?

I noticed when I plugged in the two prong connector that is somewhat hidden, feeling the blades to ensure it is plugged in correctly, it seemed to be differently aligned from when I had removed it. I believe a previous owner plugged to only one leg and shorted out the system.

So now the fuse is holding but the fan still does not work. I had noticed earlier that the fan speed switch has a 3 prong connector attached but a 4th prong is not connected. Using the multimeter I determined that 4th prong is the hot line in and the current goes to the other 3 lines depending on position of the switch. Using a jumper to bridge it to an accessory tap the fan motor ran through the 3 speeds. Yes! I'm getting somewhere!

So I now have to figure out which wire feeds the switch hot prong, tidy up the wiring under the dash and move to the next concerns. Sounds simple but there is wiring under there with no obvious connection and there is a large group attached together that may feed the gauge lights. And the horn still does not work.

I just ate supper that included collards and black eyed peas and maybe my luck is changing. I'm doing this in my spare time and he's making it worth it.

Thank you Everett and Jim.

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post #13 of 16 (permalink) Old Jan 1st, 18, 05:44 PM
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Re: Heater Fuse Blowing

Good work, Andrew,
You're welcome, Jim.

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post #14 of 16 (permalink) Old Mar 15th, 18, 07:29 PM Thread Starter
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Re: Heater Fuse Blowing

So I have everything put back together. I have the newly rebuilt alternator with the 30 amp fuse in the alternator line. The only thing I haven't done is install the three new ground straps from the engine to body and frame to inner fender.

Took the car for a ride and encountered the same thing again. Had the radio on and then turned on the climate control fan. The radio went off with the fan on and came back on when I turned the fan off. Rats! What is cycling off is the power to the radio where it saves it's settings. This is connected direct to the fuse box to fused terminal always powered. The only other thing connected there is the under hood light which shouldn't pull much current.

I took the car back to the garage and then noticed the under dash light, directly above the console, is on when it should be off. I open the door, the other interior lights come on and this one goes off. I close the door and it illuminates. Earlier today, before we went for a drive, it came on in at the same time as the other lights.

I found the cigarette lighter fuse blown. I removed the fuse box from the footwell area and tomorrow want to check if any contacts are weak.
I know this is a lot but it what I am facing. Might this be resolved with the installation of the ground straps when they finally deliver to me?

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post #15 of 16 (permalink) Old Mar 16th, 18, 07:31 AM
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Re: Heater Fuse Blowing

After eating collards and black beans, I hope you had the windows rolled down ...
Sounds like Twilight Zone.
Extra grounds might help, but as said, radio should not be dependent upon fan switch.

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