Heater bypass tube?
09-10-2012, 03:13 PM
#46
Three Wheelin'
Thread Starter
Is there not a risk of the wire meltin?
On a previous post sumone had a wire fire, i think they just looped the relay as in your pic.
But the small amp fuse will stop that.
The easyer the better so ill copy your idea "Bertrand", thanks.
Which fuse does wot?
I was told its the second fuse i need to pull, you said bottom fuse?
Just read summore old threads, the jumper wire can cause battery problems, hence the use of the 12v feed from the coil that is only live when the ignition is on.
On a previous post sumone had a wire fire, i think they just looped the relay as in your pic.
But the small amp fuse will stop that.
The easyer the better so ill copy your idea "Bertrand", thanks.
Which fuse does wot?
I was told its the second fuse i need to pull, you said bottom fuse?
Just read summore old threads, the jumper wire can cause battery problems, hence the use of the 12v feed from the coil that is only live when the ignition is on.
09-10-2012, 03:46 PM
#47
Three Wheelin'
Russ , I think the fuse is the 30 A it's written on the cover
as suggested I removed it and plug from relay position to the coil,
I am now confused to what method is best ....!?
as suggested I removed it and plug from relay position to the coil,
I am now confused to what method is best ....!?
09-10-2012, 08:45 PM
#48
Burning Brakes
IMHO, Anto's 1-wire method here is best, it is the simplest and most elegant to install and will not introduce any battery drain problems: https://rennlist.com/forums/8964599-post79.html
The wire from the coil should have a low-rates fuse in it (like 5A or 7.5A), and the 30A fuse in the regular fusebox should be removed totally.
For the guys who are having some trouble removing the cover off the coil:
It "splits" open from the front (that circular thing at the bottom is like a popstud) so you pop the front open and it'll lift off. Mine just popped open with some prising with my fingers (in that sponge opening where the small wires come out) but if it's stubborn, I suppose you could stick a flathead screwdriver into the bottom of the seam, to prise open the popstud. Make sure the car is off and the battery disconnected before messing around in this area, of course
The wire from the coil should have a low-rates fuse in it (like 5A or 7.5A), and the 30A fuse in the regular fusebox should be removed totally.
For the guys who are having some trouble removing the cover off the coil:
It "splits" open from the front (that circular thing at the bottom is like a popstud) so you pop the front open and it'll lift off. Mine just popped open with some prising with my fingers (in that sponge opening where the small wires come out) but if it's stubborn, I suppose you could stick a flathead screwdriver into the bottom of the seam, to prise open the popstud. Make sure the car is off and the battery disconnected before messing around in this area, of course
09-11-2012, 03:30 AM
#49
Three Wheelin'
Splitting it isnt the problem, but I can't for the life of me get it to lift over the coil once I've seperated it at the front
Cant see whats stopping it coming off but it just wont move. I think I may have to loosen the actual coil bracket to see if that frees it up
09-11-2012, 04:15 AM
#51
> Which fuse does wot?
On the picture bottom left from Top to bottom (1990 cab):
30 A: Engine compartment Blower
25A: Defogger (side mirrors heating on cab)
7.5A: AC compressor
> Is there not a risk of the wire meltin?
No. Only if there is a short at the back of the AC control Unit. And this is independent from the mod.
> Just read summore old threads, the jumper wire can cause battery problems,
That is because he left the fooling resistor in place.
See https://rennlist.com/forums/964-foru...***-box-9.html
> IMHO, Anto's 1-wire method here is best,
I just prefer avoiding connecting the primary of a transfo (the coil) switched at high frequency to the input of an electronic device (the AC control unit).
And it does not mix up ignition electrics with auxiliaries.
And it is simple and reversible in about 5 seconds.
The big + of the coil wire method is: No ignition, no voltage, no problem. I still would put a 1A or less fuse on that wire (HV spikes in ignition feed are not unknown....).
IMO there is no 'best' method...
On the picture bottom left from Top to bottom (1990 cab):
30 A: Engine compartment Blower
25A: Defogger (side mirrors heating on cab)
7.5A: AC compressor
> Is there not a risk of the wire meltin?
No. Only if there is a short at the back of the AC control Unit. And this is independent from the mod.
> Just read summore old threads, the jumper wire can cause battery problems,
That is because he left the fooling resistor in place.
See https://rennlist.com/forums/964-foru...***-box-9.html
> IMHO, Anto's 1-wire method here is best,
I just prefer avoiding connecting the primary of a transfo (the coil) switched at high frequency to the input of an electronic device (the AC control unit).
And it does not mix up ignition electrics with auxiliaries.
And it is simple and reversible in about 5 seconds.
The big + of the coil wire method is: No ignition, no voltage, no problem. I still would put a 1A or less fuse on that wire (HV spikes in ignition feed are not unknown....).
IMO there is no 'best' method...
09-11-2012, 04:51 AM
#52
Three Wheelin'
Freedman,
mine was very difficult as well... I think I was scared to brake it or damage anything, after 15 mm I got fed up with it, spread it a part and pull it up really hard, be carrefull not to fall on your back ....
mine was very difficult as well... I think I was scared to brake it or damage anything, after 15 mm I got fed up with it, spread it a part and pull it up really hard, be carrefull not to fall on your back ....
Last edited by kos11-12; 09-11-2012 at 05:42 AM.
09-19-2012, 01:54 PM
#53
Three Wheelin'
Thread Starter
Finally got round to makeing up little wire to replace the relay, and fitted 7amp fuse.
Now the blower works again,
Will that fuse be ok or am i better with a lower amp fuse?
Thanks Bertrand
Now the blower works again,
Will that fuse be ok or am i better with a lower amp fuse?
Thanks Bertrand
Last edited by 964russ; 10-31-2012 at 03:53 PM.
09-20-2012, 05:25 PM
#54
Track Day
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I have a '90 with what I think is the original CCU. The blower motor went bad and I lost all blower function unless the temp dial was full cold. I replaced the blower with a bypass (it was cheaper) and did the direct socket jumper shown above. I did not notice any current drain difference with or without the jumper- but it did make the blower motor work again on all temp settings. With the temp resistor removed it is hard to see from the schematics how this mod would cause a battery drain (if it is left in place is different!). The amount of current drawn by the sense lines of the CCU was just a few mA. I don't have a fuse- I don't think it is needed. I guarantee that if the CCU sense lines draw more than 1A the CCU is already destroyed- a fuse won't protect anything.
However, you can choose which bypass method you wish. The important thing is to get 12V onto the sense lines to make the CCU think the blower motor is powered.
Anyway, I live in an area that gets cold and I have honestly never needed more heat than I can get with the bypass in place. There is less heat for sure- but what is available is enough to keep warm. For me it is a no-brainer as it is both cheaper and lighter and there is no loss of heat. I don't drive the 964 when it is -20C out though- maybe then you will need a blower motor. FWIW...
However, you can choose which bypass method you wish. The important thing is to get 12V onto the sense lines to make the CCU think the blower motor is powered.
Anyway, I live in an area that gets cold and I have honestly never needed more heat than I can get with the bypass in place. There is less heat for sure- but what is available is enough to keep warm. For me it is a no-brainer as it is both cheaper and lighter and there is no loss of heat. I don't drive the 964 when it is -20C out though- maybe then you will need a blower motor. FWIW...
09-21-2012, 04:46 AM
#55
> Will that fuse be ok or am i better with a lower amp fuse?
The car has been working fine so far with a 30A, so the 7.5A is fine.
Still, if you find a 1A one day, that is safer.
There is probably no risk even with the 30A. But why take the chance?
The car has been working fine so far with a 30A, so the 7.5A is fine.
Still, if you find a 1A one day, that is safer.
There is probably no risk even with the 30A. But why take the chance?
09-21-2012, 06:21 AM
#57
Nordschleife Master
I have a '90 with what I think is the original CCU. The blower motor went bad and I lost all blower function unless the temp dial was full cold. I replaced the blower with a bypass (it was cheaper) and did the direct socket jumper shown above. I did not notice any current drain difference with or without the jumper- but it did make the blower motor work again on all temp settings. With the temp resistor removed it is hard to see from the schematics how this mod would cause a battery drain (if it is left in place is different!). The amount of current drawn by the sense lines of the CCU was just a few mA. I don't have a fuse- I don't think it is needed. I guarantee that if the CCU sense lines draw more than 1A the CCU is already destroyed- a fuse won't protect anything.
However, you can choose which bypass method you wish. The important thing is to get 12V onto the sense lines to make the CCU think the blower motor is powered.
Anyway, I live in an area that gets cold and I have honestly never needed more heat than I can get with the bypass in place. There is less heat for sure- but what is available is enough to keep warm. For me it is a no-brainer as it is both cheaper and lighter and there is no loss of heat. I don't drive the 964 when it is -20C out though- maybe then you will need a blower motor. FWIW...
However, you can choose which bypass method you wish. The important thing is to get 12V onto the sense lines to make the CCU think the blower motor is powered.
Anyway, I live in an area that gets cold and I have honestly never needed more heat than I can get with the bypass in place. There is less heat for sure- but what is available is enough to keep warm. For me it is a no-brainer as it is both cheaper and lighter and there is no loss of heat. I don't drive the 964 when it is -20C out though- maybe then you will need a blower motor. FWIW...
If that's the case I might eat some humble pie and relent and also get one.
If I do, I think I'll get the more expensive plastic 993 part because the fit I've seen of those carbon ones have been terrible.
09-21-2012, 08:05 AM
#58
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^ interested in this too
So the way to go is to remove all three (ballast, motor power, temp. sensor) plugs, tape them, and then either wire it like russ (no drain if ballast is off, too??) or like Anto (more work, but no drain)..
So the way to go is to remove all three (ballast, motor power, temp. sensor) plugs, tape them, and then either wire it like russ (no drain if ballast is off, too??) or like Anto (more work, but no drain)..
09-21-2012, 08:30 AM
#59
> So the way to go is to remove all three (ballast, motor power, temp. sensor) plugs, tape them, and then either wire it like russ (no drain if ballast is off, too??) or like Anto (more work, but no drain)..
Yes. As soon as you remove the relay, the 12V off the 30A fuse does not go anywhere: It is present at pins 3, 2 and 8 of the relay-socket (fed by a 2.5 red, 1.5 red, and 1.0 red wire according to the schematic), period.
> no drain if ballast is off, too??
No. This only possibility for a drain (with relay out and jumper in place) would be the input 519 of the control-unit somehow connected permanently to ground. If so (I've never opened one) it is probably some 4.70k resistor which gives a drain of 12/4.70*1000, about 2.5 mA, which would kill the 80Ah battery in about 30000 hours (43 months).
And that is IF only.
> So if I've got the summary of this right, the battery drain that folks were having with the single wire jumper is because the resistor was left in place.
Yes, the very resistor that they had added to fool the control-unit.
Yes. As soon as you remove the relay, the 12V off the 30A fuse does not go anywhere: It is present at pins 3, 2 and 8 of the relay-socket (fed by a 2.5 red, 1.5 red, and 1.0 red wire according to the schematic), period.
> no drain if ballast is off, too??
No. This only possibility for a drain (with relay out and jumper in place) would be the input 519 of the control-unit somehow connected permanently to ground. If so (I've never opened one) it is probably some 4.70k resistor which gives a drain of 12/4.70*1000, about 2.5 mA, which would kill the 80Ah battery in about 30000 hours (43 months).
And that is IF only.
> So if I've got the summary of this right, the battery drain that folks were having with the single wire jumper is because the resistor was left in place.
Yes, the very resistor that they had added to fool the control-unit.
Last edited by Bertrand; 09-23-2012 at 02:39 PM. Reason: value miswritten