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914World.com _ 914World Garage _ Can't get rear heater fan to come on

Posted by: 3d914 Jan 2 2004, 02:15 PM

I've been assembling all the parts to re-install heat in my teener, and now I'm down to checking out all the wiring. But I'm not getting any power to the rear heater fan (in engine bay).

I've cleaned up the connectors and wiring from the heater switch behind the shifter (ground side of the circuit). It comes out at pin #9 on the forward 14-pin connector on the relay board.

Power should be going to pin #11 of the same connector, but Im gettin zip.
This #11 connects to pin #10 of the lower-right 12-pin connector on the relay board - which bridges to pin #11 - then over to #87 of the relay.

I'm getting power at #30 on the relay - but don't have a way to check where its going from there. The relay is new, and I've swapped with others - but keep ending up with no power.

Any ideas - what I might be missing?

TIA,

Posted by: Bleyseng Jan 2 2004, 02:23 PM

Check the fuses at the relay board not the fuse box. Usually its the relay in the relay board that goes bad.

Could be the fan is toast? check with 12v from the battery.

Geoff

Posted by: Brad Roberts Jan 2 2004, 02:58 PM

Fuse or fan. Sounds like you are close.

B

Posted by: rhodyguy Jan 2 2004, 03:09 PM

you are sure that the green(i believe) wire is connected to the bottom if the heater lever on the console? and that the lever is pulled all the way up?

kevin

Posted by: 3d914 Jan 2 2004, 03:26 PM

Guys,

Yes I have checked the fuses, the fan, and the green/red wire from the heater switch. I have near-zero impedence from the switch to the #9 pin on the relay board connector.

I've swapped relays, but get the same thing - no power at pin #11 of 12-pin relay connector.

Can I do anything with the relay that would enable to see if its bridging between #87 & #30?

Or could I pull the relay and jumper #87 & #30 to see if the circuit is at least functional?

Thanks,

Posted by: Brad Roberts Jan 2 2004, 03:29 PM

This where I use a relay that I have pulled the cover off of (or us the jumper wire like you suggested).

Sorry for the fuse reference.. you didnt say whether it was good or not or whether you had cleaned the contacts for it.

B

Posted by: 3d914 Jan 2 2004, 03:33 PM

Brad,

No sweat.

Just as a mental check - am I correct that the #85 & #86 of the relay carries the ground side of the circuit, and #30 & #87 carries the + side?

Thanks again,

Posted by: Brad Roberts Jan 2 2004, 03:38 PM

You are correct. 30 and 87 always have the power.

What engine harness do you have in the car ?? The late ones have a small green jumper wire in them and the early ones dont. The harness that attaches at the back of the relay board.

I need to leave and I wont be back on until late tonight.

B

Posted by: 3d914 Jan 2 2004, 03:42 PM

Brad,

I have a late one - and it does have the small jumper wire from pin #10 to #11.

Posted by: Gint Jan 2 2004, 03:57 PM

Could be the heater motor.

I attempted to rebuild a heater blower motor without much success. Mechanically it was shot. You can see in the pictures that the choke coil from the power lead to the brush kept de-soldering itself when the windings smack the magnets due to the shoddy bushing in the bottom of the housing. Notice the grooves in the magnets.

http://members.rennlist.com/gman/porsche/74_914_heater_motor/

Posted by: boxstr Jan 2 2004, 05:01 PM

Recheck the wire connectors in the plastic block for the two wires from the loom to the heater motor. Pull on them and recheck.
Also turn the key on and make sure you have the levers on the dash in the correct position.
CCLINPTDT

Posted by: 3d914 Jan 2 2004, 05:29 PM

OK here's what the problem is: the red heater lever (behind the shifter) is not grounding properly.

I pulled it out. It has a plastic arm with the green/white lead connected to a small bead on the opposite side. When the lever is pulled back (up) - this bead connects with the metal arm of the lever.

However, there is nothing that appears to ground the metal arm of the lever to complete the circuit to ground. The metal arm is shielded from the bracket that mounts the whole thing to the body - and would ground it.

Is there something missing?

TIA,

Posted by: rhodyguy Jan 2 2004, 07:13 PM

put one lead of your multimeter on the tab the wire goes on and the other lead to clean metal on the center tunnel.with the lever fully pulled up you should have 0 ohms resistance. 0 conductivity with it pushed down. this circuit is pretty easy to follow in the haynes manual. the key does have to be on for the fan to run.

kevin

Posted by: SirAndy Jan 2 2004, 07:22 PM

it grounds to the chassis through the 2 bolts that are used to bold it down.

if you have the lever out and away from the tunnel, it won't ground ...

try grounding the green wire directly to the chassis and see if the blower runs.
key needs to be ON

Andy

Posted by: 3d914 Jan 2 2004, 11:46 PM

Thanks guys,

This varifies what I suspected. Some genious must have taken this one apart and re-assembled it so that the lever is shielded from the bracket and now does not ground like its supposed to.

I'll have to take it apart and see what can be done.

Thanks again.

Posted by: 3d914 Jan 4 2004, 05:11 PM

NEWS FLASH !!!! NEWS FLASH !!!!

I did some further investigating with the heater lever and I have my final report.

The lever portion is fully isolated from the plastic arm AND from the mounting bracket that bolts it to the floor.

The grounding connection is applied to the lever via the bead on the plastic arm. From there the arm is grounded via the .... are you ready for this? ... via the METAL CABLES that connects to the heater boxes.

DUHHHH! This is one place where I think Porsche really fell down on the design side. Unless someone can come to Porsches defense - I just don't get this one!

Anyway - its one for the books - scrap books that is!

Enjoy!

Posted by: rhodyguy Jan 4 2004, 06:11 PM

does that mean the fan now runs?

kevin

Posted by: 3d914 Jan 4 2004, 09:41 PM

Kevin,

Yes, it will when I get it installed. Still just checking everything out first. Didn't want to have to go chasing bad connections AFTER I had everything installed.

Thanks again,

Posted by: Brad Roberts Jan 5 2004, 01:58 AM

Hum. Something doesnt sound right. I knew that it had isolaters on it.. but I have used that switch for years to turn on the ground for the fuel pump relay (theft deterant).. with no heater cables or fan in place.

B

Posted by: 3d914 Jan 5 2004, 12:46 PM

Brad,

You may be one of those who have a lever that happens to touch the mounting bracket when up - which then could close the ground circuit.

THe two that I tested - One touched & the other didn't, but neither one completed the ground circuit.

I'm just shootin in the dark here with testing as I have not found any hard data on how this is supposed to work. Somebody straighten me out here.

PS: I like your anti-theft device! Have you ever bumped it while driving?

Posted by: Brad Roberts Jan 5 2004, 11:58 PM

Nope. I'm pretty tall. The crease of my knee if WAY above it when I'm sitting in the seat.

B

Posted by: banderson Jan 6 2004, 07:56 AM

I don't need no stinking heater blower, and I live in new hampshire. Above 2000 rpm, my engine fan will blow enough air to melt the rubber off my shoes.

Throw that thing away, cap off the "S" tubes and worry about something else, YMMV

Posted by: 3d914 Jan 6 2004, 08:29 AM

banderson,

But I bet you drive all winter with your top on.

Not me. Only if its raining - and even then it needs to be raining, not sprinkling. I love it - with or without heat.

No else in my family will ride with me without the heat. That works out OK most times, but other times I like to take my wife or one of the kids along.

I may even post pics of a handle disassembled for future ref. Some people may call this anal

I've found its easy to discard things we don't understand. So instead I try to understand them.

Its just my way.

Posted by: banderson Jan 6 2004, 02:30 PM

Gerard, You are quite mistaken. Last monday, and again Wednesday, were nice. It had rained over the weekend and the salt had washed away. THe temperature was in the 30s and the top was off. I have a 30 mile commute each way. I wore an extra layer and a hat but there was no traffic due to the vacation week and I was moving right along

I find that with the top off, warm air gets sucked right through and I am sitting is a pocket of warm air with a cool breeze circulating around my head. Totally comfortable, Totally awesome.

As for your blower motor, keep it, and use it if you like.

Posted by: 3d914 Jan 6 2004, 04:43 PM

banderson,

Wouldn't be the first time . . .

Keep the top off and the wheels down!

Posted by: 914ghost Jan 6 2004, 11:09 PM

Same thing happened to me, my blower didnt work when I bought the car.
Found out the blower was bad, I got a working blower.
Still didnt work, wire from lever to heater blower WAS attached, no ground though, also no power to blower- wiring in engine comp't was all present.
I could have wrestled with that little pig for a month, but:
Run FUSED wire from POS/HOT/+/15 on coil to blower, run new wire from heater switch by your right kneecap to other terminal on blower.... . ..
Then have a beer and burn some rubber. It friggen works.
R O

Posted by: Spoke Oct 29 2004, 10:57 PM

I had the same problem with my heater control. Actually had 2 controls, short one w/o center console and long one for center console. Both had the same problem that the mechanism to ground the contact gets oxidized and the lever doesn't make secure contact with ground. I solved this by getting a piece of brass wire (helps to have HO trains as a hobby) and fashioned the wire such that it contacted the side of the lever through its entire travel and attached under one of the mounting bolts.

Spoke

Posted by: rhodyguy Oct 29 2004, 11:44 PM

i wonder if the aux fan worked?

kevin

Posted by: Spoke Oct 30 2004, 12:12 AM

I also had 2 other problems, one, the RF interference coil on the motor fell off from vibration-had to be soldered back on-used silver solder-much stronger than ordinary solder.
Two, a wire inside my relay had broken-resoldered a very flexible wire back on and everything worked. Need the heater in winter in PA.

Spoke

Posted by: Root_Werks Oct 30 2004, 09:20 AM

The heater lever grounding through the cables is correct and yes, a very poor design by Porsche. Most levers pull back far enough now that they have rubbed off paint and the handle grounds to the center tube allowing most levers on 914's to still function, even though not as intended.

Good job dececting the fault! It took me a long, long time years ago to figure out the original intent of that little system.

Posted by: Rhodes71/914 Oct 30 2004, 01:41 PM

How timely that someone added to this post, saved me a search. One of my weekend projects is to try and frigure out my heater motor (rear and front fresh air blower).

Hey Dan (root werks) must of had to work today?