[Vetteman61]

I have a '71 Grand Safari wagon. It blew/melted the in-line fuse that runs from the alternator back to the blower motor. It also melted part of the harness clip where they connect. After the 2nd time I replaced the blower motor and I spliced in a new inline fuse. I also bypassed the harness connector and connected the wires myself. Today the blower motor quick working again on all speeds.

Is there anything else in the system that could be causing this? My only thought now is to replace the entire wiring from the alternator, through the harness and to the blower motor. Nothing else in the electrical system seems to have any problems or be effected.

Thanks,

[george kujanski]

What about the blower resistor assy causing the problem...don't know where it is on your car but it usually plugs into the top of the blower case on the engine side, has a 3 or 4 wire connector to it.

Got a pix of the blower case from the engine side?

George

[77 TRASHCAN]

Make sure the blower motor housing is well grounded!!!

[steve25]

Your missing another issue here, that being that should the fuse blow from excess current drawn by the fan ,the wire that feeds it, if it where the right gauge for the fans current needs would not melt

[Goatracer1]

This was a common problem when these cars were new. The factory had us replace the 30A fuse with two 20A fuses in parallel.

[Bobalong]

The alternator wire on my 70 GTO runs directly to the high speed relay on the firewall. (Thinking out loud here) So, when the blower is on any speed except high, the power runs thru the dash switch, to the resistors (which determine the speed) and then to the blower. Switching to high sends current directly from the alternator stud, thru a fuse, thru the relay and to the blower motor.
Is that how yours is ?

[steve25]

Right Bobalong, and that wire that feeds the motor on the straight thru high speed should not burn up if its the factory gauge or better, the fuse should blow first!
So I ask again is that wire of a gauge big enough to exceed the current needs of that full on running blower motor, and like Trashcan posted if you have a poor ground that will increase the current load also!
If all is right but for that motor being frozen in its bearings then the fuse should just blow like normal.

If you have a ohm meter pull that power connection off of the blower motor and set the fan speed switch to high, then disconnect that other end of the wire at the alternator and check what the meter reads, it should read open, as in no continuity! If you read any resistance you need to find out where that is coming from.

[Vetteman61]

First, thank you to everyone for the replies.

I don't think it would be the blower resister because as mentioned the high blow operates on a wire that is independent of that system, and that high blow wire is the one that is melting. You can't really see the blower motor from under the hood. It is down behind the back of the fender and changing it actually requires drilling a hole in the inner fender or removing the inner fender. I chose the latter when I recently replaced the blower motor, but the shop manual suggests drilling a hole.

I see your point about the fuse should blow before the wire melts. To my memory the fuse is a 30a, so I'm not sure why this is the case. It's interesting to hear from a mechanic that worked on these cars when new. I wonder what the original issue was that caused this problem in the first place.

My system does work with a separate wire that feeds the high blow. In my case, the high blow only works on "Recirculate" which only occurs when you move the temp selector all the way to full cold and the fan motor automatically goes to full speed. This speed is only available in this mode and the speed selector cannot produce this high speed.

I'll check the suggested items tomorrow and get back.

[77 TRASHCAN]

I've had numerous issues w/ my car since new. There was a 3 wire connector laying across the engine, the large wire got so stink'n hot it melted that connector. No problem, eliminated that connector, probably 2 years after buying car. The connections to the resistor are prone to corrosion issues, need cleaned. Then the blower relay connections also corrode, and the relay itself won't last forever.
I know some of these issues don't apply to OP, just passing it on...

My car has not been driven much lately. I am considering soldering the connections to the relay and resistor to elininate the corrosion, I'll deal with the issue of un-soldering later if needed.

The small screw on ground strap connection on the blower motor case is not the very best situation either. It uses a push on terminal to that small piece of bent metal. I plan to improve that connection some how or add another ground strap to be safe.

I re-routed my old wire harness that used to drape over the front of the engine, to clean up the engine appearance, AND to gt it off the engine. I know I added maybe a foot of wire to it which doesn't help resistance wise, but it has worked well when all the rest of the stuff functions...

[steve25]

Put some wheel bearing grease on those slip on terminals and the'll not corrode on you any longer!

[Vetteman61]

That's a great tip about the wheel bearing grease. I'm going to put that in my do-this-from-now-on mental note file.

This isn't the best picture to see it, but I rerouted all of my engine harness in one of those plastic line holders

[TSMartin]

Originally Posted by Vetteman61

First, thank you to everyone for the replies.

I don't think it would be the blower resister because as mentioned the high blow operates on a wire that is independent of that system, and that high blow wire is the one that is melting. You can't really see the blower motor from under the hood. It is down behind the back of the fender and changing it actually requires drilling a hole in the inner fender or removing the inner fender. I chose the latter when I recently replaced the blower motor, but the shop manual suggests drilling a hole.

I see your point about the fuse should blow before the wire melts. To my memory the fuse is a 30a, so I'm not sure why this is the case. It's interesting to hear from a mechanic that worked on these cars when new. I wonder what the original issue was that caused this problem in the first place.

My system does work with a separate wire that feeds the high blow. In my case, the high blow only works on "Recirculate" which only occurs when you move the temp selector all the way to full cold and the fan motor automatically goes to full speed. This speed is only available in this mode and the speed selector cannot produce this high speed.

I'll check the suggested items tomorrow and get back.

RE: Wire melting and not blowing the fuse. I work with industrial equipment and motors and those are protected with both fuses and thermal overloads. The thermal overloads will open when the motor draws more current ... and gets hot ... than what they are set for but the fuse doesn't blow. The fuse will blow when there is a sudden spike in current past the rating of the fuse. What I'm wondering is there maybe a gradual increase in the current draw in the circuit such that the wire starts melting instead of a sudden jolt of current that would blow the fuse.

I've melted several fuse holders/wires myself without blowing the fuse and have always wondered why as well.

I know this doesn't solve the problem but it may propose a reason behind it.

TS

[Schurkey]

Originally Posted by steve25

if you have a poor ground that will increase the current load also!

A poor ground should increase resistance and reduce the current flow.

Originally Posted by steve25

If you have a ohm meter pull that power connection off of the blower motor and set the fan speed switch to high, then disconnect that other end of the wire at the alternator and check what the meter reads, it should read open, as in no continuity! If you read any resistance you need to find out where that is coming from.

Are you saying there should be no continuity from alternator connector to the fan motor connector when the fan control is set to high speed? Sure about that? I would expect that since the high-speed blower relay is engaged, there should be continuity from the alternator end of the wire, through the fuse, through the high-speed blower relay, to the motor terminal connector. That is, after all, how the motor is powered when the harness is connected, and fan running at full speed--so there HAS to be continuity, and the lower the resistance the better. An open circuit is the opposite, essentially the same as high-resistance, no continuity.

Originally Posted by steve25

Put some wheel bearing grease on those slip on terminals and the'll not corrode on you any longer!

I'd have said to use silicone dielectric grease.






If you're burning-up fuse holders without popping the fuse, you'd do well to inspect the fuse holder for corroded terminals. Most of 'em aren't waterproof; the copper or brass contacts corrode; and the high resistance acts like an electric heater element--melts the plastic fuse holder.

[steve25]

No, as was posted after me fast intermittent connects make for current spikes above what is normal!

No, I am saying to look for any stray resistance to ground, as with the motor disconnected and his fans speed control unplugged that wire should read infinite on a meter.

Yup, silicone grease works great also, it's just that most folks will only have wheel bearing grease on hand.

[Schurkey]

Originally Posted by steve25

No, as was posted after me fast intermittent connects make for current spikes above what is normal!

OK, I had not considered that, and now I am. How does a current spike of such short duration that it doesn't pop the fuse, make enough heat to melt the fuse holder?

Originally Posted by steve25

No, I am saying to look for any stray resistance to ground, as with the motor disconnected and his fans speed control unplugged that wire should read infinite on a meter.

Maybe you should explain where the meter leads are placed for your testing. I can't figure it out.

[Ben M.]

Originally Posted by Schurkey

How does a current spike of such short duration that it doesn't pop the fuse, make enough heat to melt the fuse holder?

If it happens repeatedly you can get local heating along the wires that doesn't have time to cool off and can cause the plastic to overheat. Happens with circuit breakers in 3 phase motors regularly, especially if they aren't checked or torqued on a scheduled service.

[gtofreek]

There are only two reasons why a fuse holder would melt instead of blowing the fuse. Not considering obvious things like it's laying on the exhaust manifold.

#1. The fuse is rated at a much higher amperage than what the fuse holder can safely carry.

#2, and most likely cause. The fuse holder does not supply sufficient pressure to the fuse to keep a connection good enough to not create heat when pulling amperage through it. The old type glass fuses had holders that were spring loaded to hold pressure against the fuse. These connections are usually not good enough for this application and they generate too much heat for the plastic to handle. Then the heat builds, making the connection worse, which builds more heat, and this ends up snowballing until the fuse holder melts. I would suggest an ATC type fuse holder with soldered connections, or install a fusible link that is 2 wire gauges smaller than the wire it feeds. Solder all connections and you won't have a problem any more.

[Vetteman61]

OK guys. I got some readings this weekend.

I decided to break the wire into 3 sections. #1 is from the alternator to the harness clip on the rear. #2 is from that harness clip to the relay. #3 is from that relay to the motor.

Please consider I don't know a lot about reading Ohms, but I tried to research online to learn as much as I could.

First, I testing the Ohms of a jumper wire that I knew was good as a control. Each time I measured Ohms it seemed to jump around a little bit then settle down into a number and it may vary .1 in either direction.

1st: The Ohm reading was .3, and would move vary .1 in either direction. I also tested the wire on the continuity setting of the beeping continuity on the multi-meter. When doing this I got a reading of 10 and then settled down to 1.3

2nd: measured .5 ohm, plus or minus .1 ... The continuity/beep measured .6

3rd: .2 ohm beeping continuity was .5

I'm pretty sure that the #1 wire would be the culprit. It had several areas where it had been put back together and when I peeled away the very old and brittle black tape I found this abomination:


The fusible link is relatively new, but it was a 12 gauge wire, not a 10 gauge like the rest of the harness. I cannot find a 10 gauge fusible link anywhere in town so I'm going to order one from the internet and replace the entirety of the #1 wire with 10 gauge wire, just like the original... minus, of course, the terrible patches someone had in the old one.

[lust4speed]

My '67 might be different enough that this doesn't apply, but after I added an additional ground wire from the blower motor case to the engine block, my problems went away. Apparently the vibration of the fan motor, or even just the vibration of going down the road, created intermittent ground problems that created spikes and caused havoc with the wiring.

The pictured twisted wire would produce it's own set of intermittent current problems on the supply side.

Fusible links need to be four sizes smaller than the wire you are protecting, and preferably about 6" in length. So protection for a 10 gauge wire is a short length of 14 gauge fusible link. Longer link and the current carrying capacity is reduced. The fusible link copper wire is no different that regular wire, and the difference is the insulation is designed to not go up in flame when the copper melts.

[gtofreek]

Originally Posted by lust4speed

My '67 might be different enough that this doesn't apply, but after I added an additional ground wire from the blower motor case to the engine block, my problems went away. Apparently the vibration of the fan motor, or even just the vibration of going down the road, created intermittent ground problems that created spikes and caused havoc with the wiring.

The pictured twisted wire would produce it's own set of intermittent current problems on the supply side.

Fusible links need to be four sizes smaller than the wire you are protecting, and preferably about 6" in length. So protection for a 10 gauge wire is a short length of 14 gauge fusible link. Longer link and the current carrying capacity is reduced. The fusible link copper wire is no different that regular wire, and the difference is the insulation is designed to not go up in flame when the copper melts.

This is 2 wire gauge sizes smaller, since there is no 11 or 13 gauge wire.