'88 Carrera's 25 amp A/C fuse VERY HOT, but both fans are fine -- other causes?

Bob Prosser · 01:39 PM

I hate to post yet another 3.2 Carrera air conditioning / fuse / electrical gremlin thread, but after searching, I can't find a definitive answer.

Re: my '88 Carrera daily driver. Summer's here now and I use the a/c fan on its higher settings. In the last two weeks, the 25 amp fuse has blown three times (i.e., the a/c blower fan would stop). The first two times it went, I replaced it, and kept an eye on things. The third time it went, the fuse's metal band didn't just melt, but one end of the fuse was also burnt/melted away, and the area around the fuse holder had a light coating of a gray soot.

Looks like I was "this close" to having an electrical fire.

Okay, time to get serious. Research shows the main evaporator fan can go bad. The fan is almost always on at least #1 setting, so it wouldn't hurt to order a new fan from Pelican ($300 with tax, shipping).

I put the new evaporator fan in yesterday (hey, I even got the original clips back on using tape on the end of a screwdriver, pushing them on from the side). I also pulled out the condenser fan up front by the battery. I inspected it (it's brushes were fine), tested it, cleaned it, put a touch of oil on the bearings, blew out the condenser itself, and then reinstalled the unit (but I did not plug it in yet).

Assuming things had to be better now, I started the car, and turned the a/c fan on high (testing the new fan alone). The fuse started to get warm, fast. Hmm. Now I plugged in the condenser fan up front. It ran smooth and quiet, but the fuse got even warmer, faster. Not good.

I decided to go ahead and drive the car around the block with both a/c temperature and a/c fan knobs maxed to high. When I got back, the fuse was too hot to touch!

Okay, so I have eliminated the front fans, but something is still drawing way too much current. What else can it be . . . perhaps I need to replace the fan switch?

Thanks for any ideas.

Gator · 06-29-2008, 01:44 PM

I had a similar problem with my 86. Thats why I changed the fuse boxes. This may not be your problem but heres what happened to mine. The fuse clips lost their "spring" when they got hot sometime in the past. You can bend them back but they just will not hold the tension they used to have. This results in a poor connection between the fuse and its clips. I even had some fuses that welded the top of the fuse element to the clip. If you have poor connections on both ends of the fuse it can create a resistor with the fuse as the link between the two. I have seen fuses melted this way with absolutely nothing wrong with the rest of the circuit. One time this happened on a 150 amp three phase motor feed.
You could temporarily replace that fuse with an in-line fuse wired to the terminals and see if that helps your heat symptoms. The best thing to do would be to put an amp meter in with the new fuse and get a reading on the circuit load. I just got rid of the whole fuse box assembly.

Bob Prosser · 06-29-2008, 02:03 PM

Gator, thanks. Just so happens I was about to head to the shop for an inline fuse, just as you were suggesting. We'll see . . .

Gator · 06-29-2008, 04:04 PM

Let us know what happens.

Bob Prosser · 05:21 PM

Okay, so in preparation to add the inline fuse holder ...

... I took the original three panel fuse block off its mount.

On inspection I see that the copper rivet connector on the back side had gotten so hot that it was loose, so undoubtedly it created lots heat due to the resistance.

I connected the inline fuse, drove the car around the block with everything on full blast, came back, checked the fuses, and found the new inline fuse was only slightly warm to the touch. Problem fixed.

Gator · 06-29-2008, 05:24 PM

Great!! Glad you found it. I like the original stuff also but once it burns me its gotta go!

fred cook · fred cook's Garage

I think you will find that both the evaporator fan and the front condenser fan are both operated from this one fuse. When I rebuilt my fuse box I separated the load to two fuses. I have had no problems or heat issues since. Good luck with your project!

rw229 · 06-29-2008, 07:16 PM

Here is some additional info on A/C system fuses and others...

Dash lighting fuse installation

Being an '88 your car may already have the A/C fuses? The front condenser 7.5a fuse is easy, but I have never been able to find where to actually place the 16a fuse in the smuggler's box wiring. (or find a 16a fuse at a local store for that matter)

ETA... click the thread link at the top right of the above post and you will also see info about fusing the dash lights.

RussR · 06-30-2008, 01:37 AM

i've found from alot of old cars that the fuse holders build up their own resistance with age... i've had the same problem on a blower fuse on a Mercedes-Benz. I replaced the fuse holder itself and all is better!