tdiquattro

I will give it a go, thanks very much! I did look at many of the threads on this before posting, sorry for the repeat question.

I will post a couple of pics once I confirm it works ok.

964russ

Thought I'd update this thread, I started it years ago.
Asking for a definitive answer for running a bypass tube.
Ended up using the simplest option, 1 wire with 2 spade connecter.
After years of use, I've noticed it's not a mod a car that's used all year round in the UK.
You need as much heat as possible in the UK in winter, so any reduction isn't wanted
This mod will reduce air flow.

My car is a sunny sunday car, so for me, works fine.
There's enough air/heat, carbon bypass isn't perfect, but got it cheap and it looks mint.

So overall, iam happy.

StanUK951

Hi Russ, I second your thoughts on this.

I've done the one wire method and notice my fans (normal interior fans and demist) can be intermittent. It's the same without the wire and using the coil method but never did it before my rear fan got noisy. Any thoughts on this anyone?

hepkat63

I did the wire and coil mod - works flawlessly, no issues what-so-ever. Whilst I won't pretend that an Aussie winter is anything like the ones in the UK (what is snow anyway??), it piles out more than enough heat during the winter months (yes, we get down to minus four sometimes).
Only thing I will say , is that it takes about five to ten minutes to 'heat' up - so if you're after the instant heat - it's not going to happen.

tdiquattro

I finished the bypass, getting the switched 12v from the aircon compressor relay base as I do not have A/C. Easier than the coil supply.

Haven't tested it properly on a run, but the fans are running ok.

anto1150

That violet cable is the one I used... good find!

https://rennlist.com/forums/964-foru...l#post11646844

koenig_roland

Gentlemen,
i`ve some problems with the heating system in my blue coupe:

The car`s equiped with a 993 CCU. There was no G1/G19 jumber fix and the heating system was fine for some years.
Five years ago, i installed the bypass tube and did the relay fix to make the interior fans working as designed:

Last winter, my car lost the A/C system and got a header w/o heat.
No problems so far, i had no heat so no problems with heating-system. Interior-fans were working cold at every speed-step.

In autum 2015, i got heat for my headers and the problem began or i realized, that i`ve some problems there:

When setting the ccu-temperature to full cold, the interior fans are working on every speed. Adding some temperature, the fans are loosing "two steps of speed" and still working with decreased speed. To explain this: setting fan-speed to 2 on ccu and adding temperature: the fans are nearly "off". Only a small breeze of air is reaching the cabin. Setting fan-speed to 4 and adding some temperature, the fans drop their speed to "round about" ccu-speed-step 2. They blowing still a good amout of air to the cabin, but not that much like on the proper speed-step 4. I can hear, that the fans gears down. So i think there`s no probleme with air flow at some mixer flaps. The fans are getting less power...

After i realized that problem (on a cats&dogs raining 350km trip in the beginning winter),
I checked my old relay fix: The wires were still in place. Meassurements with my multimeter shows 12V above both bridges in the rear trunk fuse-box described earlier in that post. But, after some header and and engine rebuild work from my workshop, i saw, that the whole rear-blower assembly is missing. Even the failback-resistor and the temperature sensor is gone, not only the blower itself. (do i need this stuff anymore? i think the answer is "no"..)

Next step was, to check the signal on the ccu directly.
I got the CCU unit out and meassured the voltage on G1 and G19. In my opinion and after reading a huge amount of ccu topics here on rennlist: The G1 and the G19 pins are the pins which tells the ccu, that the rear fan is still in place an running properly. And when the relay is bridged like mentioned before, there must be a 12V reading according to the 12V i saw in the rear fuse box. At least at one of both pins?! On both pins, there was no voltage reading. Nothing.

Well, after some research, i saw the G1/G19 hack when using the 993 (i don`t have the full number here, but it is exactly that one that is said to work in 964 cars), so i did the G1/G19 bridge hack, but nothing improved. I`ve still no full speed on my interior fans. After that, i gave directly 12V to the G1/G19 wire bundle, going to the ccu. I thought, it could cure my problem, but still no improvement in fan speed. Now, i left the G1/G19 bundle disconnected from the CCU and even with this, no change or improvement in fan behavior... It is not that worse, because it is a summer track-day car and i`ve a heated windscreen and there is a proper amount of warm air that`s comming to the cabin, but i`m still motivated to bring the fan speed up to full-speed, even with the temperature-setting not on the blue-dot.

Do you guys have any idea for me?

THANKS

regards thilo

ToreB

thilo, you describe a typical scenario of a missing rear fan feedback signal to the CCU. If this is not present, the CCU will shut down the front fans.
Cheers,
Tore

koenig_roland

Tore, thx for your feedback.
The problem is, that the behavior is the same, even with a direct 12V connect to CCU pin G1 & G19.

Perhaps a problem, that i turned the ignition on, before i gave the 12V signal to the pins temporary?! The car is not here at my place the moment and this "test-order" was the only problem i could imagine, after thinking about my test-procedure retrospectively.

ToreB

The CCU might need a reset (battery off for some seconds) to work as normal after a detected rear fan fault.
Cheers,
Tore

koenig_roland

THX! let`s hope, a reset will cure ist :-)