BVF

First post. I recently purchased a 1990 C2 with the heat deleted and the A/C compressor removed. I plan to keep the car this way but I would like to have outside air blown into the cabin. Currently nothing happens when I adjust the CCU panel. I have checked all the fuses and they are fine. Is it possible to have the A/C fans operate with the compressor removed? How should I trouble shoot this?
Also, my speedometer does not work properly. The needle jumps around erratically while the car is in motion. Additionally the odometer is uncalibrated and ticks over at an accelerated pace (one mile actual will show 1.2 on the odo). Any insights on how to fix?

TIA

Computamedic

Hi and welcome to Rennlist!!

The operation of the cabin fans has nothing to do with the a/c. However, it has EVERYTHING to do with the operation of the rear blower and the temperature selection. In addition, the routing of fresh air into the cabin is controlled by one of the several servo motors ahead of the windscreen in the luggage compartment which operate the air control flaps in the HVAC unit. These servo motors have a reputation of failure.

Another failure source is the final stage driver fitted behind the fuse box. This drives the cabin fans.

Hope that helps.

Regards

Dave

BVF

Thanks Computamedic, those are the kinds of hints I'm looking for. I want to do a process of elimination until I can get it working. Can you elaborate on the rear blower? I'm not sure I have it installed. Here is a pic of my engine bay. In addition I am running headers, so no heater boxes and associated plumbing/hardware

joey bagadonuts

Stock motor with heater blower (left side):

BVF

Thanks Joey. So I will not be able to pressurize the cabin without the rear blower? Just to emphisize I want to be able to blow air on the front windshield to prevent fogging. I was caught in a downpour several days ago and the interior fogged up so badly I lost visibility. I can avoid this problem if I can regain the defrost function to blow outside air onto the windshield.

crg53

When you remove the rear blower motor you need to jump a relay to make the CCU work. Then you will need a blower bypass tube to connect to the heat exchangers (which you do not have ). From the heat exchangers the air goes through the flapper valves (controlled by the CCU) and then into the passenger compartment.
Without the exchangers it is very difficult to get air into the cabin, impossible to get hot air.
The first picture is from the fuse box in the engine compartment with the jumpers in place. The second picture shows the bypass tube and the rear fusebox.
With the jumpers in place you should be able to blow outside air onto the window and lower part of the cabin, using the 2 fans located under the trunk lid, behind the dash.

BVF

Thank you crg53. So are the flapper valves located in the heater boxes? if so to where are they ducted? is it possible to find the pick up point from the heater boxes and create my own ducting to source air? Where can I find a diagram or schematic of the 964 HVAC system? Thanks again for all the help!

raspberryroadster

(click on any section for blow up/parts name/number)

http://dcauto.gotdns.com/model/index/3585453/?p=813

crg53

No, the flapper valves are located just in front of the rear wheels. On a stock setup, there is always air blowing through the heating system, this air comes from the engine cooling fan but the flapper valve direct it out of the valve just in front of the rear wheels. When you call for hot air in the cabin the rear blower motor starts up and the valve directs the hot air through tubes on either side of the car under the door jams and depending on the setting on the CCU the hot air will go onto the window or to your feet or both. To answer some of your questions, yes it is possible the connect engine cooling air to your cabin, but because of no heat exchangers the air will only be warm at best.
If you go underneath your car you will be able to see what we mean, hard to explain, a picture is better than a thousand words.

crg53

Just for clearification, what I call "flapper valves" is actualy called "heater boxes", just so we are on the same page.

BVF

Thanks again crg53. All I need is ambient air pumped into the cabin during conditions when the windows can fog. Sounds like I can make this happen. I will search and learn about the relay jump.

Does anyone have insight into the jumpy speedo needle/odo problem? I've searched and found few instances of this problem and no real suggestions or solutions

TIA

Computamedic

The 1990 car has a speed signal sensor in the gearbox so there is a chance that there is a problem with that. There's not much else that can affect it. It's possibly a problem with the speedo itself though.

Regards

Dave

BVF

Thanks computamedic, I will start there. I am still looking for a good diagram of the HVAC system. raspberryroadster provided a link to a blown up view of the indiviudal components but I want to know where each of the components are located within the car. Where is the evaporator, condensor, blowers, ect located? Thanks again for all the help Rennlisters

raspberryroadster

let me know if you can open this.....let me know if it helps (bear in mind its a British file, not sure of impact of behind the dash!)

http://www.cannell.co.uk/964_Worksho..._Electrics.pdf

OUR9II

Check out Dave's links above for some good summaries, or for some oldies but goodies, see:

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

and,

http://p-car.com/diy/acdiag.html

Check out their roots, too, for more fun stuff!