Question on Fan Blower/aftermarket AC in a '73

[kilodawg]

My fan blower does not work. The car had dealer installed AC but the lower dash hardware was removed prior to my acquiring it and replaced with a non AC lower dash. I know the AC was dealer or aftermarket installed because I removed the rest of the hardware and it was pretty obviously a typical crude job with US parts.

Anyway to the question. In trying to troubleshoot my problem (I'm a complete novice on auto electrics) I noticed when looking under the dash at the backside of the slider mechanism and it's connections that there is a yellow/red wire coming from a metal plate which is part of the slider mechanism. The yellow/red wire eventually meets up with a black wire and both are joined in the back of a female connector on the other end. The connector is just hanging there without it's mating half anywhere around. In other words two wires in the back of the connector but no mating half on the other end. Also, right next to that connector is another female connector with a blue wire that is also just hanging there. Both have no place to connect to any longer.

So the question is does anyone know if the blower system was integrated into the aftermarket AC and now that it has been removed my blower circuit is just open?

Does anyone have any idea where to proceed next????

Thanks

[edmayo]

All that wiring is for installation of optional gas heater, it had nothing to do with your A/C.

[kilodawg]

Thanks good to know. Doesn't solve my problem but answers a question at least. Still not sure now where to look next though..

[edmayo]

Usually the fresh air blower stops working because of poor grounding through the slider contacts. Reach up to sliders with one hand and push on the slider contacts while sliding the lever back and forth, many times that will will break thru the dirty contacts and the fan will try to start working.

[Joe Minor]

Ed,

I'm troubleshooting a lack of blower in my 72T and want to give the above fix a try before anything more complicated. Can you describe a bit better where to put the pressure on the "sliders" before moving the levers back and forth?

I know my issue isn't the blower motor because the 4 wire plug attaching to the blower motor is not getting power to any of the wires at any blower switch position.

Does anyone know what power each of those plugs should have, and when? I think plug #1 is the ground, but beyond that I don't see why the blower motor needs 4 input wires.

Thanks,

[jameshtaylor]

Just a guess, but four wires where two would do often means different speeds...one wire for low, one for medium, etc.
Reading this over, sounds like kilodaug is talking about the stock in dash fan, while Joe may be talking about the big (often 3 speed) blower which came with aftermarket a/c?

[Joe Minor]

James,

The explanation on the wires makes sense, thanks. I am talking about the stock blower for a non A/C car. I'm pretty sure my issue is somewhere in the head unit however since none of the three wires that are soldered to the back of the fan control unit get power at any lever position (with the key to the "on" position). It made me curious that there were three wires coming out of the fan control to the blower fan, but no wire coming in. The wiring diagram makes it look like the "hot" wire might come through the rear defog switch somehow and that would be the 4th wire. But I wasn't too clear on that.

I haven't found much info in the factory manuals. I guess this is a case where the system is so simple they don't feel the need to talk about it. That's great until it doesn't work...

Joe

[jameshtaylor]

IT's there somewhere; Porsche considers nothing too small to ignore on a wiring diagram. My 74 wiring diagram shows a black wire straight from a fuse to the blower motor. A yellow, a white, and a green-white leave the blower motor and go to the fresh air fan switch. THe switch is grounded with a brown wire. When you move the lever, current can then flow from the fuse thru to ground. Clearly we're talking about two-three different speeds for the gan. I'm guessing your 72 setup is the same.

[Joe Minor]

My 74 wiring diagram shows a black wire straight from a fuse to the blower motor. A yellow, a white, and a green-white leave the blower motor and go to the fresh air fan switch. THe switch is grounded with a brown wire. When you move the lever, current can then flow from the fuse thru to ground. Clearly we're talking about two-three different speeds for the fan. I'm guessing your 72 setup is the same.

So does this mean that all three of the wires going from the switch are ground wires and in each blower setting a different wire acts as the ground and allows more (or less) current to flow through the motor and change the speeds? Its been a while since I took an electrical engineering class, but with a 12 volt motor shouldn't it either "run or not" and a reduction of current would only burn out the motor? Wouldn't it require a voltage change for more or less "speed."

I guess I"m having trouble on this Porsche electrical work because I'm having to reverse my thinking and consider switched grounding rather than switched power.

Thanks for the help.

[jameshtaylor]

Don't think so. Grounds are always brown on Porsche wiring schematics and colored wires are not. My aftermarket a/c had three speeds and four wires, only one of which was a ground. You have, I think, three hot wires and one ground. Easy enough to check with a voltmeter, or even a test bulb.