trying to remove fuse panel to fix a/c wires....

[GREASE FIRE]

the slot that holds the 30 amp fuse that powers the a/c & fan blower melted down some time before i bought the truck. I have no idea what happened but all the wires i can see under the hood and in the cab look fine so for now i am not too worried. My local mechanic said i need to remove the fuse panel, find the wires coming out of that fuse slot and cut them away from that slot, then install an inline fuse holder and re-connect. Sounds easy enough but i can not get the fuse panel out because there is so much stuff in the way, including a metal bracket that seems to be welded on to the frame. I tried to move it around a little with the two screws that hold it in place removed so i could at least see which wires come out of that slot for the a/c but i could not get a good look. Does anyone know what color the a/c wire is? that would at least help so i can know what to look for.
Also, if anyone here has ever removed the fuse panel could you tell me just how much other stuff you need to remove to get it out of the way? This is an 89 f250 if that helps.
thanks,
Paul

 

[adrianspeeder]

Exact same situation on my '88 Bronc.

I'll post some pictures on how the first attempt I tried like suggested to you failed, and then how I permenently fixed this problem.

Adrianspeeder

 

[Agnem]

According to my schematic, fuse #9 is connected to a Brown/White wire which feeds the AC/Heat dash controls. It may also start out as brown/orange.

 

[adrianspeeder]

So, yer lookin' at somethin' like this...

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Not quite sure what caused the original fault, but my guess is the old leaky windshield was dripping down a bit, cause some corrosion, cause some heat, cause some melting.

Did a quick repair by cutting the gray and yellow input wire, t'ing off to a fuse holder to the blower circuit. This was important to send power down to the fuse panel even without the blower circuit going there, as the turnsignals still needed juice.

Didn't have a problem accessing the panel by just undoing the four screws, pushing up and flipping it sideways to show the back.

Pause for my own confession.

Did this job with simple crappy crimp connectors and fast forward a year to the exact problem.

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Now this was bumped down to a 20 amp, and she still got hot from either a problem, or my crappy connections building high heat.

Whats the cure to fix all?

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Actually, I need to fix this diagram, not sure why I put a black line across the AC wire, you need to send power via the new circuit to the AC stuff too, or that won't work.

Where does this new circuit come from?

Crap, i gotta go to work, i'll finish this up a bit later.

 

[Agnem]

Interesting. My guess is that the load of the AC Clutch combined with the fan motor on full is obviously too much load for this wire gauge. I'd suggest powering the AC clutch through a relay to off-load a good portion of this current.

 

[NJKen]

It is more common than you think. The load (30A) is too much on the connector that grabs the fuse. 10 ga wire is prefered for a 30 amp load but 20A is acceptale in the automotive world. That is why newer vehicles do not have too many (if any) 30a fuses in the fuse block. The best thing you can do is rig up a high speed blower relay (like chevy did and I am not a general mills fan by any means!) It is an involved modification but well worth it in my opinion. I will see if I still have a schematic somewhere from when I did that and the GP mod I had posted on forddiesel way back in the day.
Ken

 

[GREASE FIRE]

thanks for the help so far.
although the diagram is a good idea and i would like to see the updated one, what i need most i think is an explanation of where to tap into the power source for the a/c and how to access the main wire that supplies power to the a/c system so i can fix it. I don't think it is even possible to remove the fuse panel in my truck without removing the entire dash - it is so tight in there i just see how i can do it.
right now i have the fan blower powered off the battery and controlled by a seperate toggle switch so i at least have that working, even though it only has one speed like that. From what i understand so far it may be best to keep it that way so the wires don't overheat again - so now i just need to get the rest of the a/c powered.
I wonder if i can cut into it from under the hood somewhere?

thanks,
paul

 

[adrianspeeder]

Interesting. My guess is that the load of the AC Clutch combined with the fan motor on full is obviously too much load for this wire gauge. I'd suggest powering the AC clutch through a relay to off-load a good portion of this current.

But it really isn't surprisingly. The blower motor on full only draws 6 amps with an 8amp startup peak. The AC clutch draws about .4 of an amp with a one amp peak. I was really tempted to leave the Fluke in monitor mode for a whole week after two days of driving didn't get me a spike over 12amps. I now have it fused for only 15amps in both the 88 and 79 (same problem) and never a blow or meltdown.

Anyway, at about this time I did my aux fuse panel underhood straight from the battery to add circuits for the relay wiring bypass for the headlight rewire, so I simply used another relay triggered by a key on wire to the fuel pump.

Where to tap into the blower wiring? Easier than you think, right at the blower motor! See, power simply comes from the fuse straight to the blower motor which you can easily access underhood. Then the ground of the motor is what goes into the dash controls through the speed selector switch.

T in your fused relay power to the hot wire side of the motor (brown/orange) and bam, ya sending current straight to the motor, and also backfeeding an amp or two into the stock dash wiring which will run the AC clutch. Just like I had pictured above, (minus that black line i don't know why I put there). Leaving out the stock melted fuse connection makes this an isolated stock circuit powered by a new source.

Adrianspeeder

 

[GREASE FIRE]

Where to tap into the blower wiring? Easier than you think, right at the blower motor! See, power simply comes from the fuse straight to the blower motor which you can easily access underhood. Then the ground of the motor is what goes into the dash controls through the speed selector switch.

T in your fused relay power to the hot wire side of the motor (brown/orange) and bam, ya sending current straight to the motor, and also backfeeding an amp or two into the stock dash wiring which will run the AC clutch. Just like I had pictured above, (minus that black line i don't know why I put there). Leaving out the stock melted fuse connection makes this an isolated stock circuit powered by a new source.

Adrianspeeder

so are you saying that the blower motor always has 12v at it? and it is the ground that passes through the 3 position switch on the dash? That would make sense to me except for one thing - where does the fan resistor come into play? according to what i think you are saying, the ground would pass through the resistor after the switch before the fan. But i thought it was the 12v that went through the resistor - at least that is how it is on my GM step van. So i am not sure if i follow or not.

Basically, you are saying i can fix this without even touching the fuse panel - right? that would be just fine with me if so.
thanks, and sorry for the dumb questions!
Paul

 

[GREASE FIRE]

i got it - tried it late last night when i had a moment, just did not realize it was that simple to fix. It was too late to start it up and see if the a/c compressor kicked on but my guess is that it will.
thanks again,
Paul

 

[adrianspeeder]

Correct, the fan switch is on the ground side of the motor. On high, you go straight to ground. For each position of a speed setting, ground is a leg on the the resistor with the lowest setting going through the most resistance on it's way to ground.

AC clutch will kick on if you send power to it on the same wire that powers the fan, but the other direction. Hell, ya could even fuse that for 2amps.

Also, I would pull your fan switch just to make sure it isn't melted like sometimes they do. Mine was good, but who knows.

Adrianspeeder

 

[GREASE FIRE]

now for the compressor clutch....

so i tested it out this morning. The way i have it set up is that a toggle switch supplies power to the fan and the variable speed switch on the dash controls the speed. I had to do it this way because the first time i did the modification the fan was always on unless i had a way to cut the power. So maybe i still have something wrong - but the fact that the variable speed works makes me think i have it right.
but when i started it up the a/c compressor clutch did not kick on (and i don't think the switch is melted because i checked all that out a couple weeks ago and did not see anything messed up. I don't think the compressor is seized because the thing in the middle of the pulley will turn by hand, but it just does not engage when you turn it on from the dash.
So it seems like the current is not back feeding to the clutch like it is supposed to. Anyone know how to figure that part out?
thanks,
paul

 

[adrianspeeder]

Right, you would need to use a relay triggered by a key on source to eliminate your on off toggle.

I'll look up the wire colors to find your AC clutch situation. Easy test you can do right now is, disconnect the connector from the clutch, run a wire from the battery to one terminal, and ground the other. Polarity is not important and see if it clicks.

Adrianspeeder