Hi Guys, I read through Bill G's writeup regarding bypassing the rear blower motor when using a "cup bypass" pipe to eliminate the blower assembly entirely.

I am curious why the resistors are needed to bypass the motor. Is this to prevent a fault from being logged by the Climate Control Unit? Other than logging a fault, what other benefit is obtained versus simply unplugging the motor and leaving it unplugged?

Same goes for the NTC sensor and the large, wire-wound resistor that also fits in the blower duct - if it is just unplugged, won't everything still function correctly, with the exception of a fault being recorded?

I just want to ensure that other than preventing a fault, no other benefit is gained from having resistors bypass the motor and NTC.

What did the Cup Cars do in this case? Did they just have everything unplugged, or did they have special resistors to "terminate" the plugs?

Thanks

 

I had no issues when I removed the blower motor completely and simply unplugged it. I initially left the other stuff in place so the rudimentary climate control that remains would work (I think an archive search would turn up a picture or two). Since I've now removed everything, I can say that it does not cause any faults that matter to passing emissions in CA. Of course, I don't have any climate control left either (my CCU is also gone).

 

See here.

http://www.porsche964.co.uk/technical/noheater.htm

 

axl911- yes I read that - just wondering what the point of the resistors really is other than making heat!

Tom - I keep the heat activated for defrost needs, and wanted to make sure that function still remains... plus my wife is always cold and on those early AM drives to the track, heat is essential!

 

The point of the resistors is to ensure that the CCU "knows" the stock motor/fan is still there. I think you'll find if you disconnect the fan/motor, that the CCU will shut down and refuse to play.

Note this approach doesn't work on the earlier CCU's, which were updated, I believe, in the 1991 model year (I can look it up if it's important for anyone). I know several people with 1990 964's that tried the resistor bypass, which didn't work for them.

 

Bill, where did you get the resistors... I am having trouble finding the exact ones you specify in your writeup? My local radioshack is worthless!

Thanks

 

the US cup cars used the normal heating system actually in street trim - in Race trim it retained the CCU and deleted the blower motor. I do not know if the system was functional since none of the cars were left in race trim (all current Andial numbered cars in race trim were re-converted back to race specs)
Interior View-
http://carreracupusa.org/Race/Press/Press-4.htm
Engine view
http://carreracupusa.org/Race/Press/Press-2.htm

 

Those are great pics - I like the one of all 10 cars lined up... #3 I think.

 

Ordered them online from Radio Shack.

 

Bill,
Any ideas on a '90 or am I SOL?

 

Bill, your writeup specifies a 51 ohm 15 watt resistor for the motor bypass - would a 50 ohm 15 watt resistor do the trick? I don't know if that would make a difference - my choices are 47 ohm, or 50 ohm, no 51. Thanks!!

 

For those looking around, RadioShack stinks - they have no inventory - no 15W resistors, and no 2W ones either! I found that this place had what I needed (as long as a 50 ohm is OK) with no minimum order:

http://www.mouser.com

I am curious what you mean by the CCU will shut down - that means the blowers don't run, or hot air won't blow in? I guess I can figure this out myself by just unplugging things...

 

you can change the resitance of a circuit quite easily by using them in series and parallel. If you want 51 ohm use a 50 and 1 in series. Beware of tolerances on those resistors though, will vary the resistance a good bit. Just slap a meter on it and measure it. Add what you need to get to 51.

 

Hi,

On the '90 CCU, I'm not aware of internally how they are different, or why it doesn't work. With the earlier CCU's, what happens is that the fan stops when turned on. It might be worthwhile looking through the parts catalog to see if the heater motor or other resistors in the circuit were updated at the same time the CCU was.

On 51 vs 50 watt resistors, I'd expect the 50 would work. The tolerance isn't that close.

 

The logic, i.e. the design functionality, behind the CCU's front fan shutdown is that
if the rear fan doesn't function (determined by sensing fan current) then there's
no point in running the front fan in the heat mode.