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mgatlag · Joined: 02 Aug 2007 Posts: 647 Location: Avon, IN

hey all-
I finally decided to get the heater working again in my 77.5 n/a. I have bought 4 units so far from ebay hoping one would work. What I've found is that there is two different kinds for my car. Part #477959291-A is one, and the other one is B instead of A. The "A" has 3 male leads on the metal connection board and the "B" has 2 connections. Which is correct? On top of that none of my units so far will even turn the fan on. But if I touch a hot wire from the clock to the metal board, the fan comes on, so I know that works. I just bought another unit from a guy on this forum and he tells me it works. Does anyone also know what wires behind the console go to the unit? I do have 3 unused wires with female connectors not spoken for. Also, the A/C has been completely removed years ago with only the knob left over in the console (for looks only). I really want to get this fixed so I can have heat and defrost, can't drive it if it starts raining. Help, Help!!
_________________
Michael
'77 1/2 924 N/A- 5 speed Audi box
'04 Ford Taurus - gone!!
'92 Jeep Cherokee Laredo - gone!!

Porsche... better than tea with Miss McGill
(Slap Shot)

Eturbo924 · Joined: 09 Nov 2002 Posts: 2212 Location: Londonderry NH

Hey Michael

Suprised no one has answered you here.

I have two different ones myself. The early one has the light bars actually protruding from the assembly out into the area that the face plate is. This must be the real early cars... might even be the right one for you. The other is the 1981 that I have. This had multiple wires going to the back. At least three... but one connection as I recall it had two wires going to its location. Likely a ground location. Too bad I did not take pictures before I took it out... DOU!!!!

Anyway I think I am the one you are talking to about the part you need... maybe. Let me know if you are still interested in it.

Eric
Eturbo924@yahoo.com
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1982 924
1992 968
2003 C4S
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Ozzie · Posted: Wed Sep 26, 2007 8:35 am Post subject:

You had me lost for a moment. The heater is controlled by a water valve in the coolant line.

The blower FAN is what I fianlly worked out what you were talking about.
The fans were contolled by either a slider control or a rotary control.
Both varied the resistance of the return line to earth thus varying the speed.
IIRC the fan is never off.
If your fan is not running at all (except as you described) I'd say you have wires disconnected.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

!tom · Posted: Thu Sep 27, 2007 4:20 pm Post subject:

My car also has the A/C disabled by a previous owner. I too had issues getting the fan to work.

IIRC, power to the fan goes through the A/C relay. If this has been removed, you're not going to be able to run the fan.

To remedy this on my car, I just grabbed a spare relay out of my toolbox (it's just a generic auto parts one for fog lights, horn, or whatever) and wired everything together using this, and by looking at the various wires and controls.
_________________
78 924 NA
5-lug

mgatlag · Joined: 02 Aug 2007 Posts: 647 Location: Avon, IN

Tom-
where is the relay for the AC? My Haynes book doesn't really show it. I guess that makes sense being the relay because if I touch a hot lead to the heater control assembly, I get the fan to turn on. I still have the AC knob installed in the console for looks, do I need to plug it in to complete this circuit too? It has a white plastic cluster of 4 wires.
_________________
Michael
'77 1/2 924 N/A- 5 speed Audi box
'04 Ford Taurus - gone!!
'92 Jeep Cherokee Laredo - gone!!

Porsche... better than tea with Miss McGill
(Slap Shot)

mgatlag · Joined: 02 Aug 2007 Posts: 647 Location: Avon, IN

I have a dumb question... what is IIRC mean?
_________________
Michael
'77 1/2 924 N/A- 5 speed Audi box
'04 Ford Taurus - gone!!
'92 Jeep Cherokee Laredo - gone!!

Porsche... better than tea with Miss McGill
(Slap Shot)

Ozzie · Posted: Fri Sep 28, 2007 7:41 am Post subject:

http://silmaril.ie/cgi-bin/uncgi/acronyms
If I Recall Correctly.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

!tom · Posted: Fri Sep 28, 2007 2:47 pm Post subject:

I removed the A/C knob completely and replaced it with a voltmeter. Now that you mention it I believe the power for the fan went through the A/C switch as well. This is because when the A/C was on, the A/C knob controlled the fan speed, but when the A/C was off, the lever below the knob controlled the fan speed.

All I remember is the relay is on the top row. It's too inconvenient for me to look at the car right now, but I'll try to remember next time I'm around the car. It's near the middle of the top row, but I don't know which one.

You can probably find it in the Hayne's manual.

I just grabbed my manual. You'll want to look at page 267. Switch E30 is the A/C switch, and power for the fan does go through this at times. And, J32 is quite important for fan operation as well -- this is the A/C relay we've been discussing.

Page 237 of the manual shows relay #6, 3rd from the left on the top row is the A/C relay.

Your blower fan won't work without either the A/C relay or the A/C switch if your car came with A/C, unless you do some custom wiring. The relay I wired in shuts the fan off if the car is off, and lets the sliding fan switch control the speed when the car is on. Currently it has speeds of "off", "medium" and "high," although I believe it should (and will change next time I've got things apart) to "low", "medium" and "high."
_________________
78 924 NA
5-lug

Ozzie · Posted: Fri Sep 28, 2007 6:27 pm Post subject:

The A/C unit has a shutoff relay that switches off the normal heater fan when A/C is on.
The A/C unit has its own fan.
If the A/C is removed the wiring to the heater fan is disconnected and needs to be rewired back to normal.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

mgatlag · Joined: 02 Aug 2007 Posts: 647 Location: Avon, IN

thanks for all the input guys, I'm going back home to my dad's next weekend (previous owner) and we're gonna tear into it and hopefully figure it out. Was it a big pita to wire in your own relay or should I will it be easier to use the AC switch like it used to be? I'm still also trying to figure out which wires go where to the heater control itself...
_________________
Michael
'77 1/2 924 N/A- 5 speed Audi box
'04 Ford Taurus - gone!!
'92 Jeep Cherokee Laredo - gone!!

Porsche... better than tea with Miss McGill
(Slap Shot)