87 Carrera A/C blowing fuses. Help!

mnmasotto · mnmasotto's Garage

I have a 1987 Carrera with a complete Rennaire A/C upgrade. The system was installed approximately 18 months ago. The system was running great since install without problems(one fuse). However, over the past two months I have blown two A/C fuses. The fuse only blows when the A/C is on. This would suggest its a problem with the A/C rather than the power seats or any other electrical item on the same fuse. Is this normal or abnormal? I would think I have a intermittent electrical short somewhere. Where should I start to look? The wiring looks to be O.K. however, I have not done an exhaustive electrical work-up. Any help would be much appreciated.

Thanks alot! Yes, I already did an extensive search.

mthomas58 · 08-21-2008, 03:43 PM

Any recent changes to the refrigerant charge? I had this same problem last summer after I had the system topped off. It was overcharged. Had it evacuated and recharged with the correct capacity and no probs since.

mnmasotto · mnmasotto's Garage

I just had the R12 checked. I was perfect. The high side and low side pressures were fine.

mthomas58 · 08-21-2008, 05:31 PM

Quote:

Originally Posted by mnmasotto

I just had the R12 checked. I was perfect. The high side and low side pressures were fine.

Check your three unit fuse block to make sure the contacts are clean and not corroded. Also check for cracks in the plastic block....sometimes the heat from the fuse will crack the block itself. I replaced mine while trying to troubleshoot the prob....turns out it was not my issue.

Long ugly story here.......you may find something helpful in this thread:

New A/C Problem - melting fuses???

fred cook · fred cook's Garage

Check the front condenser fan to see if it has bearing or any other problems. Look for overheated wires, etc. You can check the load it is pulling when started by temporarily wiring an ammeter in series with the +12 lead going to the motor and having an assistant turn the air on while you watch the gauge.* If it is ok, then go to the evaporator fan and check it out the same way. I would bet that one of these two fan motors is having some "issues". Good luck with your gremlin search!

mnmasotto · mnmasotto's Garage

I just replaced the front condensor fan assembly with a brand new unit from Germany. But I will check the evaporator fan motor. Can I partial disassemble the evaporator box and get exposure to the motor without disconnecting any freon hoses. I know I do not need to do this to check amperage draw, but I would like to see the condition of the fan motor.

jbrinkley · 08-22-2008, 02:50 AM

I had a fuse that would pop all the time. Took me 4 fuses to figure out it was a little bit loose in the holder, and when I went over bumps it would move a little and pop.

just a thought

GH85Carrera · GH85Carrera's Garage

Quote:

Originally Posted by mnmasotto

I just replaced the front condensor fan assembly with a brand new unit from Germany. But I will check the evaporator fan motor. Can I partial disassemble the evaporator box and get exposure to the motor without disconnecting any freon hoses. I know I do not need to do this to check amperage draw, but I would like to see the condition of the fan motor.

You don't need to open the evaporator box just to measure the amp draw. If you find the motor is the problem and needs to be replaced then yes, it is possible. It is a real pain to do. You have to be very careful to get the hollow tube out of the evaporator without bending it. Removing the clips is not to difficult and once the top is off the motor is right there. The challenge is getting the tube back in place and the ultimate challenge is getting the clips back in place. Tie a piece of fishing line to the corner of the clip so that when you drop it you can retrieve it.

DRACO A5OG · DRACO A5OG's Garage

mnmasotto,

Did you find the issue?

Mine is melting too and sometime it will blow the fuse.

System is not over charged, in fact. I keep it just under charged on purpose.

Jim

Barrpete · 08-07-2009, 06:18 AM

+1 on the condensor or evaporator fan motor. I had the same melting fuse problem - but - I believe it was actually caused by a failing voltage regulator, which in turn toasted the condensor motor. Or at least helped it on its way. So you may want to check your charging voltage.

Which brings to mind another point. The factory did not put a fuse on the condensor fan motor. So if you haven't added one already now would be a good time.

86 911 Targa · 06:54 PM

mnmasotto,

Before engaging in a prolonged analysis, and spending a lot of money replacing parts,
here is what I would do.

Having incurred the same intermittent failure mode on our '86
(blowing fuse #2), this was my approach.

Cleaned all of the connectors/fuses in the A/C circuit including the relay next to the
evaporator housing.

These connectors carry a fairly heavy amperage load and do corrode over time
producing a series resistance in the circuit thereby pulling excessive amperage,
and in some cases destroying the connector.

In our situation, a corroded/destroyed condensor fan connector was the bad guy.

The connector is located in the front of the car next to the jack.

If all of the above, and other posts, does not resolve your issues, pm me and we can work this
by phone and start lifting output wires on fuse #2.

Good luck,

Gerry

mnmasotto · mnmasotto's Garage

Thanks for the reply. I am still having the same issue. It has become a real problem. What usually happens is, I convince my wife to take the Porsche to go somewhere like out to lunch or shopping. We will be cruising along with the A/C going and it will all the sudden blow a fuse. The temp in the cab will immediately rise from 70F to 85F until I pull over and change the fuse. Very embarrasing! I will clean the connectors this weekend and see if that helps.

My evaporator fan has started making some low level noise. I am wondering if anyone has found a way to replace the evaporator fan motor. My car is a 1987 so the Griffiths re[lacement fan will not work. I think a new motor with higher flow will really improve the performance of the system.

DRACO A5OG · DRACO A5OG's Garage

Well, it looks like I am in the same boat. I would love to work side by side to see and compare what the issue may be.

Will be in Anaheim Sunday to help RnLn on his Slant Cab

Barrpete · 08-07-2009, 07:41 AM

One other thing to check - although its a longshot. If you have power seats these are on the same fuse as the AC. An intermittent short in the power seat circuit could also be the problem.

As for the evaporate fan, you can get areplacement motor from Pelican. Or you can probably score an older style box from the used parts page and and upgrade it with the Griffiths fan. That's one of the things on my rainy day project plan.

DRACO A5OG · DRACO A5OG's Garage

When I installed my Sub-Woofer under the passenger seat, i had to remove the seat and disconnect the power seat, wire accidentally touched and it popped the fuse.

Unfortunately, my melting/popping fuse #2 occured way before I installed the sub-woofer and it appears to occur only when I run the blower at full speed.

Other times at medium or low I never have the issue. But I never checked. Will replace Fuse and observe.

Luckily, it will only melt after an hour or so trip pulling in to my parking structure.

DRACO A5OG · DRACO A5OG's Garage

Update:

Used my wire brush set Dremel to clean the contacts to a mirror finish.

So far so good no more shrinking fuse due to heat that causes a short or blown fuse.

It must be the combo of Front Condensor fan and A/C Blower Fan's resistance because I hear both of them making abnormal squeeking noises. But Definitely the cleaning helped me.

Will need to take the two apart and clean and lube them. I also understand the A/C Blower's Fan needs to be placed properly to insure proper clearance. I unfortunately messed with it the last time I replaced it.