Melted A/C Fuse with picture

[ghiaholic]

Searched the archives but didn't see much about this specific issue. A/C suddenly stopped working. Checked the fuse and it was loose in the holder. Pulled it out and it had melted on the bottom, so with the spring pressure of the holder, it compressed so that it no longer made good contact.

My question is why it would melt but not blow? If it were an amperage issue, it should have blown. So maybe it's a contact issue? Could this be a bi-metal issue where an aluminium fuse is used in a copper holder? I'm thinking this may be the case. With the smaller, lower amperage fuses, the resistance across the aluminium to copper connection wouldn't be such an issue, but with a high current draw circuit, a proper copper fuse may be required. If I can't find one of those, perhaps some electricians paste that is used for Cu/Al connections.

Or is this a symptom of a different problem? From another thread I see Draco had a similar issue - did this ever get resolved? http://forums.pelicanparts.com/porsche-911-technical-forum/556486-fire-front-condenser-blower.html

[DRACO A5OG]

There is too much resistance in the line, I ended up replacing the fuse block, but it still get some shrunken fuses when is use both passengerside window while ac is on. My windowd is bindy, so taht could be the culprit in my case, but when I did swap to a new fuse block it was much cooler when ac was on versus the old fuse block.

[fred cook]

Depending on the year of your car, that fuse could be powering the evaporator fan and the front condenser fan. Those combined loads will be pretty close to 20 amps. Any corrosion or looseness in the fuse holder will create enough heat to melt the fuse. The best thing would be to separate the load and put one on a different fuse. Typical problem with the original 911 fuse panels.

[ghiaholic]

Found a few 25A copper fuses in my old parts stash so I'll see if this reduces the contact resistance and resulting heat. If not I'll have to consider either the fuse block swap or a second fused circuit.

[kuehl]

What year is the car?

[DRACO A5OG]

Oh no do go higher amps it may do worse and melt your wire/s, stick with oemamps, never ever put higher fuses then spec, it will melt wires for that component, your fuse did it's job and killed itself before wires fried.

It's an 85

[ghiaholic]

The car is an '85. PO installed a second blower over the front condenser and tapped into the existing circuit for power, so the load may indeed be nearing capacity for the 25A fuse.

I'm curious about my theory about the bi-metal resistance so I'll keep an eye on this copper fuse to see if it resolves the heat issue. If not my next step will be to disconnect that second condenser fan even though its presence in the circuit doesn't cause the fuse to blow.

[fred cook]

There are a couple of things that you can check at the fuse box. First, make certain that the spring clamp holds the fuse firmly in place. Then, use an eraser on a #2 wood pencil to clean the contacts on both ends. Check the wires where they are connected to the fuse block terminals. If they look to be at all corroded, loosen the holding screw and remove the wire(s). Use some spray electrical contact cleaner on the wires and fittings. If the fitting is badly corroded, use a .22 caliber brass cleaning brush to remove the corrosion from the holes. Reinsert the wires and tighten the clamping screws. This may or may not solve your heat issue. Fuses 2-5 or 2-6 (counting from the back of the car) are jumpered together on the rear of the fuse panel. The brass connector is fastened in place with brass rivets that tend to come loose over the years. The resistance may be being created there. In that case, the only solution is to replace the panel. Good luck!

[kuehl]

Originally Posted by ghiaholic

The car is an '85.

The front condenser fan draws about 5 amps nominal running. The fix for that was a 7 amp fuse between the front condenser blower motor and the feed.
Have the "PO" wire the 2 front condenser fan's with their own 7 amp fuses before the feed; if 1 fan fails you will still have the other.

Does your car have electric seat controls and do they all work (both seats all controls) ?

[GH85Carrera]

The cheap replacement aftermarket plastic fuses are a big part of the problem. The proper ceramic core with copper wire is the proper fuse. I have seen many of the plastic fuses do the same thing.