sml

There are threads resolving problems, but hopefully if I can find the best solution, I wont need to understand all the technical details of what can go wrong & why

I think my car is a M series, 91 ...

Is the current best solution to ..

Step 1 ... buy 51 ohm 15 watt wirewound resistor
Step 2 ... 18K ohm 2 watt resistor
Step 3 .. install as per http://www.porsche964.co.uk/technical/noheater.htm

crg53

I did this and it works perfect. Remove the blower motor relay and jump the terminals. CCU works as it is supposed to and no battery drain. As you can see from my signature, your and my car are the same MY.

sml

Thanks. Just a bit confused ... either ..
a) you followed the website link and it is perfect, or
b) you followed the website link + the extra relay jump step and it is perfect

I think you must mean (b) .. so the website directions are almost perfect with the extra step? is that right?

what happens if you do not jump the relay?

Shamus964

Also a 1991 here... I jumpered the wires in the relay as above, but I also retained the stock resister (the coiled wire that clips inside the stock heater pipe). No battery drain and the CCU works as it should.

If you don't jump the contact where the relay resides, the CCU will not function correctly and you'll get the blower fans doing weird things (short version).

sml

Thanks

So what we are saying is that the webpage DIY is a bit dodgy as there is no mention of the relay jumper?

Shamus964

Oops, didn't notice your link in the original post - the DIY may be what's required for some folks since the CCU's changed in various years, but I didn't follow it.

In a nutshell, for me all I needed to do was:
- Disconnect the battery
- Remove the blower fan assembly and disconnect all the wires (with the exception of the stock resistor) I just zip-tied them out of the way
- Remove the relay
- Jumper per the pics
- cut hole in bypass pipe to fit stock resister
- install the bypass pipe
- install stock resistor
- connect tailight and distributor vent tube to bypass pipe
- reconnect battery
Enjoy!

Ducks964

If you jumper the relay, you do not need the fancy resistors that are in the DIY webpage.

sml

Ahh ... thanks. Jumpering the relay sounds easier & cleaner. This almost makes sense now.

But ...
a) Shamus964 said he had to cut the hole to fit the stock resistor.
b) The DIY guide says ... the last resistor (#3 in picture) is the long one with the curly metal wire that's stuck in the side of the original air pipe. It's there to break the electrical circuit should the motor develop a short, so, for simplicity, it was left alone.

What difference does it make if the curly resistor is stuck into a slighter warmer airflow?

Ducks964

Airflow temperature should be basically the same since it is still coming from the main engine fan. Since there is no motor once you pull the blower, the resistor probably does not do much.

sml

So really, the process is as simple as just 'jumpering the relay'. Finished.

ThomasC2

yeah, that's it if you don't have a strange version of the CCU or some other electrical fault.

Thomas

vasculardoc

Is there a significant difference between doing this for 1990 and 91 cars ? I understand there might be - is that why there are some differences in the DIY ?

Ducks964

My understanding is that for 89-91? the jumper process is the only way it will work. The process with the resistors to fool the CCU does not work on the early MY's.

Dave White

The jumper process doesn't work on early cars, with or without the resistors. For a/c, the front fans work okay unless you turn the temp **** all the way up in which they shut off. For heat, the front fans do odd things, randomly cycling on and off. I ended up updating to a later model ccu and providing a dummy load to get everything to work as it should.

GT TWO

I have a non AC 89 car and my CCU has a mine of its own anyway hot, cold, hot cold.

Last week my blower motor got stuck on so I am going to a bypass pipe. Hopefully it will work ok.

Not bothered about heat in the car as my car is for track days but I do want to de mist the screen so hopefuly it will be ok.

Will report back.