a/c fan switch wiring help

[rogwilson]

I am replacing the a/c fan switch on my 1980 911 sc. porsche updated the switch and the new switch is labled differently. ugh!

old switch: terminal B = gn/wt to temp switch
C = red to relay AC
L = red/gn to evaporator fan resistor
M = red/bk to evaporator fan resistor
H = red/wt to evaporator fan resistor

new switch: terminal I= ?
II=?
III=?
IV=?
fifth terminal labled "+" and "MRO" =?

If anyone has solved this puzzle let me know, I hate to let murphy's law take over and guess at it. thanks.

roger

[ruf-porsche]

Does the switch looks like the old one? Perhaps the terminals on the new switch is similar to the old switch.

[rogwilson]

ruf

the switches are similar but labeled differently. i decided to apply alittle logic and hooked up the new switch to a 1.5v battery and used a voltmeter to test the circuit in the off and three fan positions. i was able to determine which terminal corresponded to low, medium, and high fan speeds. next i consulted my bentley manual and determined which wire carried high, medium, and low voltage to the evaporator fan resistor unit.

the conclusion: terminal + = red (a/c relay)
I = red/green (low fan speed)
II = red/black (medium fan speed)
III = red/white (high fan speed)
IV = green/white (to ac temp switch)

i hooked the switch as above and presto it worked. the previous owner must have had it wired wrong, since the old switch burnt up and the first fan position was high instead of low. now it appears to be in order and will test tomorrow on the road. we need alittle a/c in indiana about this time of year.

[jdowty3]

Was the switch you installed a OEM replacement or an aftermarket switch? My AC Fan switch has just failed and the temp here in Dallas is 105 F.

[rogwilson]

jim

the switch I installed was an OEM replacement. the porsche dealer said they updated the switch and the old style was no longer available.

A/C blower switch prt# 91161324300
switch nut prt# 91161311902
switch collar prt# 91161311902

There computer showed a picture of the old style switch (metal), they ordered it and when i went to pick it up, only the switch nut came in. They reordered and on trip number two the updated switch came in (plastic), so the parts man tried again to reorder the switch to match the original. On trip number three they figured out the old switch was superceded. Since this was my third visit and they were tired of seeing me, they gave me all three parts for $20. If yours is the old style switch, you may still find it somewhere on the internet or Pelican.

105 degrees, wow, and I thought it was hot in indiana without the air pumping. Hope you get yours fixed soon!

[Richard559]

I have a 1980 911SC and had the same problem with the switch. Thanks to rogwilson for doing the research sorting out the wiring was made clear. My old switch came out in one piece so I shot I picture of it and labeled the pin out for reference. The only issues I have left are that the old knob does not fit as snugly on the new switch and 2nd and 3rd position are reversed. The fan blows hardest set on #2 position. Since I had the whole A/C gone through my guess is the car wiring is flipped or something. I was out of time so I just left it and I’ll have to get back to it later. Could the wiring on the car be flipped near the line to the resistor?
It makes since to me that someone would do that because the old switch was just about falling apart and most of the contacts were sloppy one was completely burned. Prior to this my Evaporator blower froze up. So I took everything apart Replace the Evap motor, cleaned everything up, put on a pro cooler and a new under dash vent form Griffith’s. What a difference! Now I just have to sort out the switch.

Thanks Rog that switch pin out really helped.

[spiderduct]

I found the origional (exact replacment, no modifications) A/C-HEATER FAN SWITCH (INDAK 3 SPEED ROT) 5 BLADE for my 81 911SC. The are available at ALL POINTS B.U.S, Inc. ( allpointsbus.com) for $8.95 each. 1 (800) 852-9298

[slkash]

Thanks Spiderduct! I just received a replacement switch from All Points BUS for my '79 911 SC Targa. It was a simple task to remove and replace, now I can enjoy all 3 fan speeds again.

[thstone]

Thanking you all for this info 14 years later!

[Dnolte6]

I called All Points and they two types of A/C switches. One that has a short length of threads and one with approx 3/4” length of threads. Which one do I get.