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Where is the heater fuse - 79 fuse panel different from AIM

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Where is the heater fuse - 79 fuse panel different from AIM

 
Old 04-03-2012, 11:55 AM
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BernieM
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Default Where is the heater fuse - 79 fuse panel different from AIM

Have an issue with the heater not getting power. Motor is good (tested with separate feed), switch is good (tested with multimeter) but there is no power getting through on the brown wire that feeds the switch. The problem I have is that I can't figure out what fuse is supposed to feed power to the switch to check it.

Here is a picture from the AIM.



It shows B as the fuse for the electric choke and heater. I don't have a fuse in that spot. My panel matches the AIM except for slots A and B. I have a wire in slot B.

Here is my fuse panel:



I do not have A/C but I put a fuse in that slot and still no power. I checked the fuse in slot R for elec fan and it is good. What am I missing?
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Old 04-03-2012, 08:38 PM
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The fuse marked "Elec Choke & Heater" has nothing to do with the heater in the car- it's for the electric choke heating coil and relay.

I'd look at the one marked "D" in the AIM. A/C fuse might also be the one for the heat fan.

One question- Why is there a 30 amp fuse in the gauges? IIRC they used a 5 amp fuse.
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Old 04-03-2012, 09:06 PM
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Tim
I put a fuse in the 'D' slot labelled A/C and still got nothing. I had to remove a melted fuse so I thought that I would be good to go and the slot was a bit corroded. I cleaned the slot, checked there was juice, put in a new fuse and still no power to the heater switch. That's why I am trying to figure out where else to look. Any other thoughts?

As for the 30 amp in the gauges - not my doing. I got the car a year ago and have been rebuilding it after a crash.
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Old 04-03-2012, 09:30 PM
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Fuse D is the correct fuse... If you pulled out a melted fuse you may have an issue on the wire behind the panel. Pull the panel from the fire wall and check this.

But.... for it to melt the fuse I'd have to say you have a dead short somewhere. Have you check the resistor on the heater box to make sure it's not shorted out? Also check the high blower relay where the wires connect to it. They are famous for having the connectors dry out and crack. When this happens the wires can short out.

This may help you trace down the problem.


Last edited by Willcox Corvette; 04-03-2012 at 09:32 PM.
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Old 04-03-2012, 09:30 PM
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the power must go through a connector after it leaves the fuse, c125 before it reaches the switch, check the connector under the dash.
http://www.corvetteforum.net/c3/tune.../index16.shtml
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Old 04-03-2012, 09:55 PM
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Thanks for both diagrams but the car DOESN'T have A/C. Any comparable charts for a car without A/C?

Is there still a connector/resistor under the dash and if so where am I looking?
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Old 04-03-2012, 10:15 PM
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The A/C cars got an extra harness. The diagrams Willcox posted up will get you there. GM was really good in using the same wire colors thru the entire product line- GMC, Chevy, Olds, Pontiac, and Buick- the wires all did the same thing for "x" color.
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Old 04-04-2012, 11:48 AM
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I'm still perplexed. SpeedReed8 mentioned looking uder the dash for the connector but any of the diagrams I look at including the AIM show the relay and connector in the engine compartment. Before I start tearing the dash completely apart does anyone know where the parts are in a 79 without AC because they are definitely not in the engine compartment.
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Old 04-04-2012, 12:42 PM
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The fuse goes in the AC slot (Even if you don't have AC) The picture looks as if that slot is melted pretty bad. So, my guess is there is/was something wrong with the circuit that caused the meltdown. You need to figure this out. On my car it destroyed the fuse socket and rendered the fuse, and the rest of the blower circuit unusable. I can share how I fixed it, but it wasn't pretty.

This is where I would go next:
1)Check to see if there is continuity between the fuse block and the brown wire on the AC/Blow resister connector, pin 50 on the Wilcox diagram. (inside the engine compartment by the passenger side firewall)
2a) If yes -- check to see what the resistance to ground is -- with the connector disconnected it should be infinite -- If it is not, you need to find the short.
2b) If No -- the fuse connector is corroded/disintegrated, or the brown wire is open. Most likely directly behind the fuse block.

If you finished 2a you need to check the resistors and the relay for shorts

Good luck

Last edited by wajulia; 04-04-2012 at 12:54 PM.
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Old 04-04-2012, 02:56 PM
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Where is the AC/Blow resister? It is not in the engine compartment from what I can see.

Here is a shot of the connections on the motor:



The wiring diagram I have shows the orange wire from the switch feeds the motor (which jives with the picture) and also goes to the heater resistor (orange, yellow and light blue connections) so I need to get to that to check it. These wires from the switch head under the dash.

Is the resister under the dash? Before I tear the dash apart am I missing something obvious.
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Old 04-04-2012, 03:05 PM
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Just found this picture. It was with the resistor part for corvettes w/o A/C. I assume this is what I need to get at and it looks like it is inside the car under the dash. Anyone agree or know for sure?

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Old 04-04-2012, 09:52 PM
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It does look like it's inside the car. But I have to admit I've never seen one inside. (Maybe I wasn't paying attention?) Even so, it shouldn't be impossible to get to.
And yes, that is the resistor you need to get to.

After you installed a new fuse in the A/C slot, you did check and make sure there was power on BOTH side of the fuse? And then from there go right to the switch and check the brown wire for 12v.
It's possible that the brown wire is cooked at the back of the fuse block and open right there too. Grab a meter and (key OFF) check the brown wire back to ground.
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Old 04-04-2012, 10:34 PM
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Originally Posted by TimAT View Post
It does look like it's inside the car. But I have to admit I've never seen one inside. (Maybe I wasn't paying attention?) Even so, it shouldn't be impossible to get to.
And yes, that is the resistor you need to get to.
Confirmed that the resistor is inside the car. If you remove the glove box you can get your hand on it behind the ducting although I will need to pull a lot out to test/change it. I want to make sure it is the culprit.

Originally Posted by TimAT View Post
After you installed a new fuse in the A/C slot, you did check and make sure there was power on BOTH side of the fuse? And then from there go right to the switch and check the brown wire for 12v.
I cleaned the fuse slot after I took out a melted fuse and checked that there was juice but not with a fuse in the slot so I will do that. I could not get juice on the brown wire after I put a fuse in but the wiring diagram shows an orange wire from the same slot to the ignition switch so any chance that is involved?

Originally Posted by TimAT View Post
It's possible that the brown wire is cooked at the back of the fuse block and open right there too. Grab a meter and (key OFF) check the brown wire back to ground.
I think there was a lower amp fuse in the slot so I was hoping that was why it melted in the slot. New to the multimeter - are you talking about checking the resistance on the brown wire?

Thanks
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Old 04-05-2012, 10:33 AM
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[QUOTE=TimAT;1580471829]After you installed a new fuse in the A/C slot, you did check and make sure there was power on BOTH side of the fuse? And then from there go right to the switch and check the brown wire for 12v. QUOTE]

Power on both sides of the fuse. No power to brown wire. Thoughts?
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Old 04-05-2012, 07:14 PM
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Thanks for the help everyone. Definitely the problem is on the brown wire between the fuse and the connector. I ran a separate line to the connector with a 25 amp fuse, connected it and power. So now I have to track down the problem on the brown line.
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Old 04-05-2012, 07:36 PM
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You're making headway. Set the meter on the OHMS scale and check the brown wire at the switch between both the fuse block AND to ground. If the wire is broken (burned, cut), the meter will show infinite resistance. If it's shorted to ground, that's why the fuse pops. YOu don't need a fancy high dollar meter either- a $10 one works for this every bit as good as a $200 one. Between a meter and a plain old 12v testlight, you can test just about anything on your car that's electric. Later (81-81), you need a meter with 10Meg Ohm resistance to check some of the computer sensors.
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Old 04-05-2012, 10:51 PM
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So.. I see this is a non air car.. and right now, you won't need a schematic. If you do post again I think I have one for no a/c... (odd not to have a/c on a 79).

Anyway.. If you by-passed that brown wire and it works I'd be very suspect of what else the brown wire took out when it cooked. You may want to look at the harness and possibly peal it back. We have a transmitter that we trace wires like this with and it will tell you the point of the break. You probably don't have that option... but I would look at the harness tape and see if there are any signs of melting. Then break open the tape and check the wires surrounding that same brown wire...

Usually when a wire gets so hot it gets cooked it will take out the surrounding wires in the harness and then you never know what you'll get as far as shorts and issues.

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Old 04-06-2012, 01:10 AM
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Excellent advice.....which is coming from a source that has probably seen it all.
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Old 04-07-2012, 10:13 PM
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Don't know if you are talking about me Charlie.. but if so, TY..

I don't think I've seen it all....LOL.. But after removing a shift console that had the entire underside injected with expandable foam it does make me wonder..


Last edited by Willcox Corvette; 04-07-2012 at 10:40 PM.
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Old 04-10-2012, 01:31 PM
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Originally Posted by Willcox Corvette View Post
Anyway.. If you by-passed that brown wire and it works I'd be very suspect of what else the brown wire took out when it cooked. You may want to look at the harness and possibly peal it back. We have a transmitter that we trace wires like this with and it will tell you the point of the break. You probably don't have that option... but I would look at the harness tape and see if there are any signs of melting. Then break open the tape and check the wires surrounding that same brown wire...
I didn't get an email that there was a reply but thanks for the advice and I will do that. I am having some wiper issues so I have some good posts on checking that but I wonder if that may be something that was affected by a melt down?
Cheers,
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