A/C Condensor blower fuse

[FrankM_]

Hi,

in a recent post discussing 'upgrades' to a 911 Carrera, fusing the condensor blower motor and the instrument lights was high upon the list of 'need to do'.

This weekend my A/C blew the fuse (setting on 3 for prolonged time). I initially replaced the fuse with the same fuse (red - 16A). Upon arriving home the new fuse was again relatively hot. I checked the Bentley manual and it says to put a 25A (blue) fuse in (pos 2) !
When checking the schematics for the A/C it seems, in my '85 at least that both motors (evap and condensor) are fused through this 25A. I tested this (remove fuse) and I cannot get any of the two motors to work.

Now the question : do I need to install an extra fuse as suggested in a previous post ? On per motor ? If so, what amperage should the fuse have ? Or is the single 25A fuse enough and did the previous post refer to older models ?

[86 911 Targa]

I posted "Added fuses" a while back.

The A/C on our 86 was under fused.

Find my post for an answer to your questions.

Also, keep the contacts for your A/C fuse (#2)
very clean as corrosion will cause a series resistance,
and the fuse will get "toasty" warm.

Gerry

[blucille]

my fuse holder had already suffered some harm earlier in life.....i separated the other loads onto their own fuses, and put the blower motor onto a small automotive circuit breaker that I mounted right next to the fuse box. clean, neat, easy. It hasn't tripped even once.

[GH85Carrera]

Also try to get the ceramic core fuses. The plastic fuses may work for a while, but if they get warm, they tend to squish down and not work over time.

Clean the contact area top and bottom on the fuse. Use a new ceramic based copper material fuse, not one with aluminum. Electricity, copper to aluminum is not a good thing.

[Peter M]

Originally Posted by FrankM_

…...Now the question : do I need to install an extra fuse as suggested in a previous post ? On per motor ? If so, what amperage should the fuse have ? Or is the single 25A fuse enough and did the previous post refer to older models ?

Hi Frank,

The issue is that in the event that the front blower motor seizing due to age, exposed condition or dry bushes, the small gauge wiring harness appears to melt well before the standard 25 amp fuse will blow. Consequently the common way is to install a 8 amp fuse into the existing blower motor harness near the motor or to buy one of these that simply plugs into the existing sockets shown on this page as "Front Condenser Fan Update Fuse Harness"

https://www.pelicanparts.com/catalog/SuperCat/911M/POR_911M_ELSWCH_pg4.htm#item11

Funny, it says a fused harness was standard fitment on '87 to '89 cars but my '88 didn't have one!

I haven't added an extra fuse in the evaporator blower circuit but I know some people swap out the relay to a fused type. I noticed that my '88 already had one fitted but don't know if that was a standard fitment or done by a previous owner.


Don't forget the ashtray light and the ventilation control lights too. My ashtray light holder failed and shorted and burnt about 2 metres of wire and shorten my lifespan by a couple of years when the cabin filled with smoke!


If you Google search the above issues you will come across plenty of posts and photos showing details of solutions owners have developed.


Regards
Peter


EDIT: He's one good thread from Gerry with photos: Added fuses & relays.

[FrankM_]

Many thanks for all the answers, I will get started on it right away (both the condersor blower, evap blower and interior lights).

Since the condensor blower is is close to the battery, it might even be better to use a fused relay (8A) and put in an extra wire from the positive battery terminal? That way at least the FUSE2 (25A) in the fuse box will see less current drain as the front blower gets it's own fused source ?

[Peter M]

Originally Posted by FrankM_

Many thanks for all the answers, I will get started on it right away (both the condersor blower, evap blower and interior lights).

Since the condensor blower is is close to the battery, it might even be better to use a fused relay (8A) and put in an extra wire from the positive battery terminal? That way at least the FUSE2 (25A) in the fuse box will see less current drain as the front blower gets it's own fused source ?

Frank,
That might be regarded as going overboard BUT it would then allow you to reduce Fuse 2 down to a slightly lower current rating to better protect the wiring to the evaporator blower as well.

More than one way to skin a cat they say!

[GH85Carrera]

All of us like to admire the engineering on the 911. Fact is, during the leadership at Porsche AG of Ernst Fuhrmann (1972 to 1980) the 911 suffered lack of budget. For whatever reason Ernst Fuhrmann hated the 911, and wanted to kill it outright. It was still selling at a profit so he could not kill it, but he did not want it to hang on. He forbade any spending on research and design updates for the 911 models. So the 911 engineers had to work in secret to figure out how to add air conditioning and wiper delays.
Only after the American, Peter Schutz took over as boss at Porsche did the 911 get a reprieve, and a budget to improve the model.

The lack of budget is why the wiper delay is a little bitty knob on the dash and totally separate from the wiper switch. The gauges are not fused, and many other weird "only in an air cooled 911" things.

Try to name another car that has the heater, the factory installed AC, and the fresh air system as three distinct systems. No other car can run all three at once. It is easy to have the heater blasting out gobs of heat, the fresh air blowing on the dash, and the AC blowing cold air on your face all at the same time.

[86 911 Targa]

^^^^^
Here are the A/C current draw modifications for our '86.

Best,

Gerry

[86 911 Targa]

[img]
^^^^^
A/C condenser fan fires.



^^^^^
One of these might have prevent the above
The 3.2 car A/C fusing was not It's finest hour....................

Best,

Gerry