New A/C Problem - melting fuses???

[scottb]

Originally posted by fred cook
These are the kinds of problems that finally pushed me into replacing the fuse panel with one that uses ATO fuses.

And, IIRC, your installation of the ATO fuse blocks was fantastic! You might post some pictures to give everyone an idea of what you did.

[rick-l]

I just noticed there is a ferrule on the end of the wire. What does that look like?

[fred cook]

Basically I built an aluminum mounting bracket that holds 24 ATO 20 amp rated fuse holders. The mounting bracket bolts directly to the old base. There are several jumpers on the backside of the old style fuse holders that you will have to replicate. I spent a lot more time studying the wiring harness than actually doing the conversion! This is no place or time to mess up. Here are some pictures:

This is the new fuse block before mounting:


This is the fuse block mounted in the car and wired:


Notice that there are 3 extra fuse positions available.

This is the new fuse block with the original cover installed:



Since doing the fuse conversion, I have had only one wiring issue and that was due to a bad connector crimp (my fault).

[mthomas58]

Nice work Fred!

No luck on the fuse block clean up & repair. Melted another fuse on the way home from work. Stopped by dealership on the way - new fuse block should be in tomorrow. If that does not solve problem then on to further troubleshooting with the multimeter.

Is this supposed to be fun?

[fred cook]

Have you checked the load that is being pulled across that fuse? A quick check with an ammeter will tell you if the problem is the holder or the load. I could not tell how many distribution wires are coming off that fuse, but if more than one, you might have to separate the load and add a fuse.

Good luck!

[mthomas58]

Fred, I have not checked the load yet.

I have inquired what the total amp draw should be for the compressor, evap fan and front condenser fan should be (< 25 amps obviously) but no replies.

I have thought about adding an addl circuit and taking some of the load off the A/C circuit, but want to make sure I don't have an overload problem with one of the components in circuit first.

BTW, there is only one distribution wire coming out of the fuse.

Thanks for your help!

[nyne11]

Long Shot....................You haven't overcharged the sytem by any chance putting more load on the compressor???
Dave.

[mthomas58]

Originally posted by nyne11
Long Shot....................You haven't overcharged the sytem by any chance putting more load on the compressor???
Dave.

Specifically asked the tech who charged the system right B4 the problem started this question and he emphatically stated that charging the system would not cause this.

He recommended replacing the fuse block as a starting point citing that the fuse block is a common failure in this age car.

[fred cook]

I think you will find that only the condenser fan and the evaporator fan work off the fuse in question. The evaporator fan works thru a relay but the front condenser fan I believe does not.
On my SC the combined load for the two fans was slightly over 20 amps. When I rebuilt my fusebox I split the load between two fuses.

[rick-l]

Originally posted by fred cook
Have you checked the load that is being pulled across that fuse? A quick check with an ammeter will tell you if the problem is the holder or the load. I could not tell how many distribution wires are coming off that fuse, but if more than one, you might have to separate the load and add a fuse.

Good luck!

25 amps is greater than the range of most multimeter's measuring current. So you would have to go to Radio Shack and buy a 0.1 ohm resistor.

A multimeter does not seem to be an item in his toolbox.

Originally posted by nyne11
Long Shot....................You haven't overcharged the sytem by any chance putting more load on the compressor???
Dave.

The electrical load the clutch presents has no relation to the load on the compressor.

[Barrpete]

Originally posted by fred cook
I think you will find that only the condenser fan and the evaporator fan work off the fuse in question. The evaporator fan works thru a relay but the front condenser fan I believe does not.
On my SC the combined load for the two fans was slightly over 20 amps. When I rebuilt my fusebox I split the load between two fuses.

I believe the power seats, if so equipped, run off this fuse as well.

[carnutzzz]

Originally posted by rick-l


A multimeter does not seem to be an item in his toolbox.

Busted!!!!!!

He's a carpenter for Godsake, not an electrician...

[mthomas58]

Originally posted by carnutzzz
Busted!!!!!!

He's a carpenter for Godsake, not an electrician...

I've been exposed!

[mthomas58]

OK, fuse block replaced with new one and overheating problem remains. Disconnected front condenser blower and circuit still overheats, so evap blower or A/C clutch is drawing too much amperage. Could there be a prob with the smuggler's box relay?

I think this is beyond my capability to troubleshoot this any further so next step may be the dealer.

[fred cook]

unplug the wire going to the a/c clutch compressor. If you still melt fuses, the problem (almost) has to be in the evap. fan. In the process of being replace, the wrench could have done something to bind the fan or armature.

By the way, my multimeter will measure up to (I think) 25 amps. I got it at Lowe's or Home Depot from the electrical department. Or, you could go to your local auto parts store and buy a cheap ammeter gauge. They usually read up to about 30 amps. It would not be as accurate as a multimeter, but would be "close". For a little more $$$ you could buy a digital ammeter gauge and be very close!

[mthomas58]

I seem to have the overheating/melting problem only when running the evap fan at the highest speed.

Any chance something is amiss with the fan switch/resistor pack?

[Mysterytrain]

the evap motor looks to be very much like the footwell and the front condenser motors. I know that the footwell type motor pulls about 8 amps running in the fast speed. I would guess that you motor is on the way out. The bearings might be beginning to bind and causing the motor to labor. You might get of cheap by taking it apart and cleaning and oiling the bearings.

[rick-l]

Originally posted by mthomas58
I seem to have the overheating/melting problem only when running the evap fan at the highest speed.

Any chance something is amiss with the fan switch/resistor pack?

The problem almost has to be in the fuse block.. They don't catch fire to interrupt the circuit.

What gets hot first? Does the fuse bridge wire itself get hot? Which side of the terminals gets hot? Is that crimp on the wire corroded?

I know you don't have a multimeter but maybe you could put your left index finger on the upper screw and your right one on the bottom screw and see which one leaves a bigger burn mark.

I would bet a cheapo Radio Shack multimeter and some playing around learning what it does would be cheaper than driving by the dealer mechanics.

[mthomas58]

OK Rick, you're making me admit that I have a meter but don't know how to use it other than to do simple continuity tests. I don't find the insructions very useful.

Found some tutorial info on the web that I need to study.

The jumper on the top of the fuse block gets hot first. The fuses melt on both ends so its hot on both sides.

Confirmed that it heats up regardless of fan speed. When the compressor kicks in it starts to heat up.

[aj88cab]

Mark

Lets asssume the new fuse block is good. It seems that if the fuse is still getting hot and melting the fuse body at BOTH ends there is one of two things causing it.

1) Too much resistance between the fuse and fuse block posts.
or
2) Too much current thru the fuse.

If it is "1" (excessive resistance) there is a problem between the contact points at both ends resulting in excessive heat. Since we assume the new fuse block is good that leaves the metal of the fuse strip as suspect.

If it is "2" (excessive current) the fuse should "blow", but it doesn't. So if there is too much current (which must be checked and corrected if it is the case), the fuse should be blowing. So again the fuse is suspect.

So my question is - have you been using the same "brand" of fuses? And if so, my potentially over-simplified suggestion is to try another brand of fuse and see if it melts too.

Good luck
Andrew