raymond-turner

Guys, is it possible? My CCU (non air-con) has given up the ghost. Rear fan not working, oil cooler fan not working, CCU not working. I'm about to hard wire a switch to turn the oil cooler fan on, my questions are, can I replace the CCU with a series of switches, all I need is, fans on, heat, full speed to de-mist, fans on, full speed, heat for feet, fans on, full speed for fresh air, fans off. Doe anyone know which wires I would use from the rear of the CCU to access fanss, oil cooler, heat mixer servos and direction servos.
Many thanks in anticipation. Raymond, ex of the home of the bacon butty, now chilling out in delightful Cobham.

Computamedic

Raymond,

I think a lot depends on just how comprehensive you want the controls to be. The CCU does a lot of coordination between several sensors to operate the fans and servos to get the air where you want it and at the right temperature. Doing things manually is likely to be horribly complex - or just a dismal failure. In a race car there are fewer creature comforts needed and a simpler situation to control but in a road car you have all the variables from motorway driving to stuck in a traffic jam.

From your list of needs I think the easiest solution is to get the CCU repaired - or get a replacement.

Regards

Dave

mjshira

this is something I am interested in doing, has anyone done it?

mojorizing

I think it's possible. Each servo would need a double pole, double throw, 3 position switch. Center is off, right is one polarity, left is opposite polarity. #4 and #5 of each servo is the motor and each of these go to either the "K" or "G" connector on the back of the CCU. Oil cooler relay, engine blower relay , same thing, they're lead from the back of the CCU.

However, bet your bacon butty you have a seized servo, a seized blower, etc. which overloads and burns up the servo drivers in the CCU. You'll need to test each servo/motor blower also.

You need chapter 7 of the workshop manual that contains the connection to the CCU.

Does your CCU have one or two buttons for the A/C fan?

mjshira

great post, thanks. my car is a 1990. There is a button on the left side to turn on the a/c. However, I've deleted the a/c. What I'd like to do is control the basic functions of the ccu with toggle switches. I can sacrifice some features.

raymond-turner

Hi, managed to get my ccu working (ish).
What I was hoping to do was wire the following options,
Air flow up or down.
Heat on or off
Fans on, max or off
oil cooler fan, on or off.
Sounds like a simple request, having looked at the internals of the ccu, I got scared, very scared. I've seen less in a mobile phone... Cheers. R

springer3

I once looked at doing this on Mercedes CCU's which are similar. It is theoretically possible, but the continuously-variable controls are difficult to replicate with switches and manual control. The climate control is brilliant when it is working properly. It turns out to be far less work to fix the thing. Like a lot of German electronics, CCUs suffer from cold solder joints and blown transisters, which are tricky to find but easy to repair. Usually the CCU is fine, and there is a failed component elsewhere. Does your CCU still throw diagnistic codes?

mojorizing

Good question - what trouble codes does it throw? If it's a 993 part no. then can you "drive links" and test each component?
The 2 connectors in the back of the CCU are active parts from AMP/Tyco but they don't have them in stock, so making your own pcb is not an option unless you take them from an existing CCU.

IanR

You could pick one up on eBay - there's a couple at the moment:
http://cgi.ebay.co.uk/Porsche-964-RS...6.c0.m14.l1318

and

http://cgi.ebay.co.uk/Porsche-911-96...6.c0.m14.l1318

PS was it you I saw between Cobham and Chertsey weekend before last? I was on my way to GT1 to drop the car off for a re-seal (oil leaks)

mjshira

I really do want to pull this off. Does anyone have a good wiring diagram of the CCU and associated devices?

mojorizing

I don't think the schematics of the CCU are public knowledge. Tonight, I'll try to photograph a CCU that I have open. See if there's enough detail to see the traces,etc.

There's not enough detail to be able to trace the circuits from a photo.

Jamie Summers

Anyone know if a right hand drive CCU will work in a LHD car ?

thanks,

Jamie

Computamedic

Jamie,

I'm pretty sure I've seen the question asked before and the answer was YES. The buttons are just organised differently but I don't know if the connections to the wiring loom might come from the other direction. I would suggest waiting to buy until you get a definitive answer from someone who's done it though.

Regards

Dave

Kahdmus

careful with the part#'s if you pick up a used one. There are some variations and its easy to pick up the wrong one..

raymond-turner

Revive an old topic.

Winter is coming......

Does anyone know which wires on the back of the CCU operate the rear, engine cooling fan?

Looking to over-ride it to force de-misting.

Any clues, directions for the wiring would be appreciated.

Thanks guys.

R