ernestedward

Recently I replaced the heater blower motor since the old one was shot. Right after I replaced it I connected the switch and it worked fine, but then other things on the car took precedence and I just let it sit. Now that everything else is back together and working, the heater fan doesn't come on from the switch... First things, I checked the fan itself with 12V straight to it, came on no problem. Then I checked the switch with a continuity checker, and it seems to be working normally. With each click the continuous circuit moves one pole, with a constant ground. I also swapped in a spare audi switch my neighbor had (exactly the same) with no change. Then I checked voltage at the plug that the switch goes into, and I got a 9V drop between the ground and each of the poles. Is 9V normal? Is there a rheostat that brings it up to 12V before the fan? Anyway, I also checked the fuse, it looks good. Other than a broken wire (unlikely and a nightmare situation), what could be the problem? What else should I check?

AznDrgn

check your ground wires.

ernestedward

Which ones? All the poles are getting a good ground otherwise they wouldn't read anything. I checked again and it's more like 10.5V, btw. Fuse is definitely good. I just can't get power TO the fan plug, no matter what I do.

AznDrgn

There should be one behind the fuse panel on the firewall and another behind the center console at the firewall. Just because you get a reading doesn't mean you have a good ground. Bad grounds cause resistance which in turn causes low voltage readings. You have to think of the entire circuit, you can have an absolutely perfect hot wire but with out a ground you have no circuit and therefore no power to whatever it is your trying to get to work.

jyoon

your blower motor resister is probably dead. depending upon year, i think it may mount to the motor.

ernestedward

Checked that. From closet to ground to furthest, I believe the values were 3.5, 6.5 and 9.5 (could be off on the last one). Is there somewhere I can check if these are correct? Haynes didn't have it, as far as I could find.

Granite 944

I have no actual experience with this happening, but if you have power to the switch, and you know the motor itself is ok, it probably is a open wire on the motor resistor pack at the motor. Early cars have resistor pack visable on side of motor, late has the resistor pack underneath the long white plug on top side of motor assy housing.
Please put your model and year of Porsche(s) in your signature, it helps us all alot, most the time.

Granite 944

Opps........I see you've already checked the R-pack. Maybe the blower fan relay? IIRC, its in the 3rd relay from the left side, top row on the early relay box. Don't know about late.

ernestedward

My car's an early interior, still. How do I "check" a relay? I've got a multimeter, what should I do with it?

jyoon

shake the relay. if it sounds like parts are rattling around, replace it if it's not too expensive. bad ones usually make some noise. that's my unscientific method.

AznDrgn

The relay probably has at least 4 prongs on it. 2 are going to be the winding and 2 are going to be the switched legs. figure out which one is the winding by testing continuity between two prongs the one pair that show up open line are the switched legs and the pair that aren't open are the winding prongs. Now take a DC 12V power source or you might be able to get away with a 9V battery and attach it to the winding prongs. That should close the relay and you should now have continuity on the switched legs. Sometimes there are diagrams on the side of the relay that might help illustrate what I'm trying to say.

ernestedward

Checked the A/C system (#3) relay using above method...relay had some corrosion on the winding prongs, cleaned it up, tested it, and reinstalled it, no luck. None of the other relays seem to apply, except MAYBE "cooling fans" but those are working fine. What else?

Granite 944

I just took a relay out of a '83 parts car relay board (easy to get to), and tested it. It should be part number 141.951.253B. It is a 4 prong relay. Put 12volt power between # 85 and # 86, you should hear relay click in, and there should now be continuity between # 30 and #87.

Anyone else ever noticed that the relay position callouts at most the vendors, and in Parts and Technical Reference Catalog show this fan relay in the #1 position, and the AC relay (cooling fan relay) in the #3 position according to their diagrams of the relay boards, which is opposite in reality (at least, on both of my cars)? Or am I really, really confused?

Granite 944

You said there was corrosion on the winding prongs. Remove the relay again, and check and make sure voltage is getting thru the relay prong at the relay box. Maybe the back of the relay board and its connectors are cruded up bad enough not to allow voltage flow into the relay? Do you have the screen off of the blower motor right now, so you can check actual voltage at the fan plug, just to make sure your getting battery voltage when blower switch is at highest point?

ernestedward

Granite - You were right. There was corrosion in the relay box. I took out relay 3 and liberally sprayed WD-40 and pushed it in and out a few times. Everything works fine now. Thanks a lot.