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Unhappy '84 auto heat problem

Hi,

I have an 911 '84 model 3.2 SC with auto-heat. The 9 position and permanent on variety, no levers.

I've seen this heating topic gone over time and again here but not covering my particular situation.

My the main engine compartment blower has worked until recently. The actuating arm on the switch control between the seats functions as it should when selecting anything above 0 and moves the heat control valves correctly. I do have residual heat just about flowing.

I have removed and tested the rear blower and it works just fine off a 12v source.

I have a temperature sensor between the sun visors and in the rear left of the engine compartment have two controller boxes the rearmost being the 'heater controller' (shown here removed), others on the forum refer to the controller as being between the seats, I'll refer to that as the 'heater switch'

I have no individual small round relay in the rear but have the 3 fuses as usual. The top one is connected only on one end and they warm up both sides when the switch is set to 10

I have checked continuity of the circuits as best I can with my limited knowledge, including the two block connectors just behind the switch control and all appears sound. The three switches giving out the binary code under the dial on the switch control work fine.

I've removed and opened the heater controller in the hope I could see something burnt out. I do see what looks like 2 relays inside, the larger of which I assume is for the blower. This 'controller' has 12 pins and I think is about $150 (I could spend elswhere on my pride and joy)

I've found articles showing how to test a normal relay (pins 85-86 and 30-97/87a) but nothing about this controller and the wiring diagram shows all wires to and from it dissapearing into the ether . I found this wiring diagram and the excellent article accompanying it elsewhere on the forum but it doesn't help me much. On the Engine Compartment Controller I wonder what the WT/RE to the speedo can be all about?

When switched to blow the two top blue fuses get warm, current is detected both sides of the fuses and oddly on a couple of occasions when the engine is revved hard the blower sometimes springs to life and work perfectly for a few seconds (I thought perhaps vibration may have an effect on a bad contact, but then there is also an increase in voltage)

I don't have the luxury of being able to swap this controller with a similar car and am loathe to shell out $150 to discover this is not the problem.

Does anyone on this fantastically helpful forum have any ideas on how to fault find the various components and how best to go about tracing this fault or at least narrowing down my search. What are the various symptoms when something goes wrong with auto-heat system?

Please, no one tell me to get levers etc., that's not the point, I want this system to work as it is and it's become real cold and wet here. (UK) ALL help from any source would be much appreciated.
Old 01-11-2004, 02:56 PM
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The speedo on my 86 stopped working and the auto heat defaulted to full on heat with the dial only allowing me to turn the heat on and off.I assume the speedo input tailors the heat to match engine fan speed. A speedo rebuild fixed it.The previous owner of a recently aquired 1980 installed a new headliner and "deleted" the interior temp sensor ,my controller still controls the fan but now I must use the heat overide lever to set temp.Good luck finding full details on trouble shooting many of us would be interested .
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Old 01-11-2004, 03:44 PM
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Mmmm, thanks for that. My speedo works OK or at least I think it does.

Does anyone have any knowledge of the relationship, if there is one between speedo/blower/controller
Old 01-11-2004, 05:07 PM
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Gary,

Your observation that the motor sometimes runs with increased voltage makes me think of a bad connection - perhaps a ground. I'd take a careful look at the multi-pin connectors. Look for corrosion or, in the motor leads, burnt/overheated connections.

I don't see this being related to the runs-with-increased-voltage observation, but, regarding components - there is a temp switch which enables the relay for the blower motor. It's located under the throttle body, or thereabouts. If it's failed or disconnected, I suspect the blower wouldn't work. You should be able to check the wire connection to the switch with a well-placed mirror & light. Since it supplies a ground when up to temp, I would try grounding the appropriate pin on the relay, bypassing the switch, to see if that allows it to run.
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Old 01-12-2004, 07:46 AM
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Thanks for that Mark, sounds like an excellent lead and promising. Trouble is I can't locate the switch that you mention and it's difficult to trace back from the controller through the harness. I've even checked PP and others for the switch you mention or P/N to guide me in what I'm looking for, so, I've just whipped out the motor to see exactly what's in back ! Could you discribe/mark the location for me please.

By the way, the 'appropriate pin' on the relay/controller is pin 10 and when connected is inaccessible.
Old 01-13-2004, 04:33 AM
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The Bentley schematic calls it the "fan temperature switch", page 970-48, bottom of the page near the center. The Porsche Parts & Technical Reference Catalog shows it as # 47 on page 21 in the "crankcase" section. It's located on the breather cover. [I believe I can see it in your picture, but I don't have the editing SW to provide you with an arrow...]The part number is 930.606.118.00.

HTH!
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Old 01-13-2004, 04:51 AM
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All now becomes a little clearer. I've marked to switch, will check it out and let all know the findings later. Must go to the dentist for the mo.
Old 01-13-2004, 06:02 AM
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No, that's not it, Gary. Drop down to the breather cover, which bolts to the top of the case, and look for a sensor screwed into the cover with a single wire attached. The wire should be BRN/BLK.
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Old 01-13-2004, 06:29 AM
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Got it Mark. You need to be a magician to get in there though. As it was I used my 15yr old son's hands, then verified the cable with my own eyes. Black covering and inside was the expected BRN/BLK single lead. The spade terminal on P/N 930.606.118.00 doesn't look like mine though, I have a push on tip long thin nipple but it's definitely the one. I've amended the picture to reflect the location. I've not pinpointed the location exactly 'cos all was done by touch 'n' mirrors and the picture's not from the best perspective.

Now the bad news, having taken off the lead I shorted it to earth, with and without the motor running with the same result, nothing, and with the switch in all positions

The earth connections are made on the top of the left/rearmost inlet manifold and were removed, cleaned and resecured.

Any more ideas on how to check the heater controller?
Old 01-13-2004, 01:38 PM
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Trouble-shooting that heater controller without a schematic of its innards seems like a crap-shoot, IMO... One thing you CAN do is try to isolate whether it's the cause of the bizarre blower motor behavior. To do that, I would use a volt meter to observe the voltage at the motor [at its connector]. If the voltage fluctuates coincident with the motor speed, then you can go to the uncovered controller and check the voltage at the input and output of the relay. You can also observe the relay in operation to see if it's moving or is solidly picked.

It's interesting to note that the blower motor's ground is on the #1 intake runner, but it gets there via a connection on the back of the alternator [according to the Bentley schematics]. This should be kept in mind if you find voltage variations across the leads at the blower motor.
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Old 01-13-2004, 02:49 PM
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Coming to a brick wall now, I thought I'd take the problem to my friendly local autolecky who seemed to show some interest.

He took the cover off the heater controller and we ran a test with it in situ. We manually made the circuit on the left hand relay shown and lo and behold everything fired up with the ignition on and engine off. He seem to think the controller is gone west so I think the next step is to bite the bullet and buy one/suck it and see. My only worry is that something else, maybe the controls between the seats are not passing the current hence the failiure of the relay to actuate, the power for which, I think, is supplied on pins 9 and 11 (forgot to check them). However if that only was the case methinks the other settings which do not uses pins 9 and 11 should actuate the relay.

So, in summary, the blower and it's circuit seems fine as is the main power supplied by the relay. The problem seems to be with the relay not actuating. SO, let me check how deep my pockets are.

I've just found one here in the UK secondhand for 45 ($82) p&p inc. That'll do me thank you and what's more the nice guy has said "If there's a problem with it, send it back and I'll send you another" (there is a God). New, UK, I've been quoted $250. WOW.

I'll let you know how I get on, it'll be a few days.

Last edited by GaryGriff; 01-14-2004 at 04:22 PM..
Old 01-14-2004, 08:17 AM
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I'll be anxious to hear the results, Gary. Tough one, indeed!

best of luck.
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Old 01-14-2004, 09:39 AM
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Gary

Great Post - I can't see the pics so am having some trouble identifying the components and their locations! I've done some similar work on my '88 which had a problem with the footwell blowers and related to temp sensors in the end. If the site comes up I'll see if I can help more!

Where are you getting spares from in the UK?

Regards
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Last edited by Roy M; 01-16-2004 at 01:15 AM..
Old 01-15-2004, 11:30 PM
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Yipeeee hi oooohhhhhh, at least that's what the experts say.

The heater controller in the engine compartment was at fault and now all works perfectly.

It seems the heater blower circuit was fine, displayed by the fact that when the relay inside the controller was depressed with a finger the blower functioned.

The switches in the control unit between the seats were working fine ('cos I checked if they were making and breaking the circuit with a multitester set on resistance. The switching power for the relay comes from this source.

The actuating arm operating the flapper boxes in the rear was working fine.

Anyway, it's all go now, I've learnt where all the parts are and have a pretty good idea where to look if something happens next time.

I will take the old realy to pieces though an let everyone who subscribed to this post know what I found out. It would be nice to know what broke and if it could be sorted with a soldering iron and 50cents.

Thanks to all who made comment and tried to help.

Last edited by GaryGriff; 02-06-2004 at 05:50 AM..
Old 01-20-2004, 07:20 AM
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Congrats, Gary!
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Old 01-20-2004, 07:24 AM
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