A/C blowing fuse

[FrankM_]

Hi,

I have been working on getting the A/C overhauled with the fantastic Griffiths stuff. Yesterday I finally had some time to go and have the A/C recharged. While recharging/testing, we put the AC on max and after only 3-4 minutes the system stopped.

Looking at the fuse box the 25A fuse had melted, the conductor part was still OK but the plastic had melted and shrunk not allowing any current to pass anymore. (Not how it should break).

Today, I put one of the other original ceramic fuses in its place (cleaning the contacts again) and had a short test. It hasn't blown but it does get hot to the touch. Approx 50°C if I can believe my IR thermometer on such a small target.

Measurements :

A/C Off : 0 Amps through fuse
A/C On:
Voltage drop over fuse : 0,09V
Amps on circuit near relay in smugglars box : approx 15 A
(that is motor+pwm controller + magnetic clutch)
Amps on condensor blower motor : approx 4 Amps
Let's say 20 Amps all together

0,09 V * 20 A = 1,8 Watt

Can/should the fuse become so hot from this ?

Can anyone else measure the V-drop - at full A/C setting - across this fuse ?

Does anyone have good place where I can order real ceramic torpedo fuses here in europe. I can only find these plastic ones here ? Or should I just go for an extra cable from the battery and a separate blade fuse of 25A ?

[GH85Carrera]

That fuse powers a lot of stuff. It is normal to get a little hot. Step one is order some ceramic bullet fuses and replace any of the poor design plastic fuses. Then get some steel wool and polish up the contacts top and bottom and remove any crud or oxidation. No need to go nuts, but just a clean contact point. Then install the ceramic fuses of the proper amperage. Spin them around and make triple sure they are seated centered on the hole.

Something like this is what I bought.

https://www.amazon.com/dp/B07FPDPCLT/ref=cm_sw_em_r_mt_dp_2GPWC6K0DP94NK67K6XW

Last time I looked our hose did not sell the ceramic fuse replacement kits.

[Hotshot]

Check your power seat switches. Ask me how I know. Also I did have the AC pop with a crappy plastic based 25amp fuse. Use ceramic ones and make sure contacts are all clean.

[FrankM_]

I checked my seats, no problem, no power draw when not using the switch.
My problem os indeed I cannot find real ceramic fuses.
I would like to have the Littlefuse ATS series as the draw should be half of what I see now (50 mV at full use) but nobody seems to sell them.

All links I got link to plastic+ metal fuses ...


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[GH85Carrera]

Just do a search for Ceramic bullet fuses. Often the local VW dealership has them. Mercedes used to use them, as did BMW.

You should find a source for the set like I post the Amazon link for above.

[86 911 Targa]

As per the previous poster, the A/C fuse #2 does carry a heavy load.

And does over heat.

I relocated the A/C condenser fan wiring to another fuse.

No more issues.

Best,

Gerry

[mo-mon]

Same thing happened to me. Most sellers advertise their fuses as ceramic BUT are actually plastic. Still on the hunt for true ceramic ones.

[mo-mon]

To the OP Frank, try the fuses made by Flosser, Germany. Maybe you can source their real ceramic ones in Belgium.

[FrankM_]

Originally Posted by mo-mon

To the OP Frank, try the fuses made by Flosser, Germany. Maybe you can source their real ceramic ones in Belgium.

Thanks. Will search for them !


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[FrankM_]

Originally Posted by 86 911 Targa

As per the previous poster, the A/C fuse #2 does carry a heavy load.

And does over heat.

I relocated the A/C condenser fan wiring to another fuse.

No more issues.

Best,

Gerry

Good idea, where exactly does this red 1.5 mm2 wire splice of the 6mm red departing the fuse ?


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[86 911 Targa]

Originally Posted by FrankM_

Good idea, where exactly does this red 1.5 mm2 wire splice of the 6mm red departing the fuse ?


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I'll post some pics on Monday.

Best,

Gerry

[Jonny H]

It’s a half truth that the plastic fuses are to blame.

The other factor is the holder itself. This has brass rivets on the back which lose their contact and corrode over time. This creates a resistance in the holder itself and the whole thing heats up.

Fitting one of our fuse panels will solve the problem.

[Mike Andrew]

Had the same issue. Contacts finally self annealed to the point that the fuse would not fit tightly. I spliced in a blade fuse holder, which fits nicely under the fuse panel cover, and the issue was resolved. Not stock/original but it does work.

[dhanl82]

It is always a good idea to clean and make sure a ceramic fuse is installed, however due to the way Porsche wired the car, there is still quite a heavy load on fuse 20 with both the evaporator and front condenser motors running off it. On my 1982 SC I moved the red/green wire leading to the condenser from fuse 20 over to fuse 19 which is for the headlight washers - since I do not use them at all. This provides a separate fuse for each fan and ensures that neither fuse has very much load.

Hope this helps

Dave

[FrankM_]

Originally Posted by dhanl82

It is always a good idea to clean and make sure a ceramic fuse is installed, however due to the way Porsche wired the car, there is still quite a heavy load on fuse 20 with both the evaporator and front condenser motors running off it. On my 1982 SC I moved the red/green wire leading to the condenser from fuse 20 over to fuse 19 which is for the headlight washers - since I do not use them at all. This provides a separate fuse for each fan and ensures that neither fuse has very much load.

Hope this helps

Dave

That's what 86 911 Targa also suggested and what I will do. Will try to find where it splices from the main power lead. That should be close to the fusebox I guess.

[FrankM_]

Maybe to debrief :
- with the original ceramic fuse it works (and thoroughly cleaned the contacts)

- in reality, the Griffiths motor moves so much air I don't put it anywhere near maximum, so power consumption is lower and doesn't blow the fuse. In addition, in my 1985 with the extremely small side vents and the relatively small center vents, it really doesn't make a lot of difference anymore after 3/4 of the blower motor speed is on. I guess it's a limitation of the air distrubution 'system', it only creates a bit more noise.
(But the new Griffiths motor is way quieter than my original one)

- I will move the condensor blower to the other 25A fuse (headlight washer) just to separate out these 4-5 amps (that is what I measured this motor at)

- I am still looking for Littlefuse ATS of Flösser ceramic fuses in Europe, but so far only found the plastic ones. Probably some plastic ones are good enough but mine were melting so hard to tell and I am not going to experiment and buy them all.

And, this is the first day this year where I could really use some A/C and it works quite well. 'Colder air' after about 1,5 min. Cold air (measured about 4-5°C on IR thermo) after 8 min of driving in a heat-soaked car.
I don't have a third condensor as I still live more than 51° North from the equator ;-)

Now let's hope that it holds the charge well and that I don't need to go on a leak-hunt.


Frank