Toddimus

Hi folks,

I haven't posted in quite some time, but it's high time that I get to fixing some issues, so here's my situation.

I've got battery drain that I've narrowed down to the climate control unit. The little fan on the rear of the unit ALWAYS runs when the ignition is off. The only way to get it to turn off is to pull out fuse number 1 and re-install. This only solves the problem until the ignition is turned on again.

What you can do to help me... it's easy. It will take less than 5 minutes, including the time it takes you to respond to this post....

Check if the lights on the A/C, recirculate, and defogger buttons still illuminate after the car has been off for more than 20+ minutes. Mine do, but I bet they're not supposed to. It seems the CCU is constantly powered up, thus the little fan runs, and my battery goes flat in about a week.

If you're still interested read on, maybe you can give me some more ideas...

After searching, reading lots of posts and everything related to the system in Adrian's book, (aside from having learnt more than I thought I'd ever know about the climate control system), I think I've got a bad CCU (Climate Control Unit).

The unit itself is p/n 964.659.047.01, which seems like it's not even really the right one for the car (according to Adrian's book). I looked and the wiring modification (shorting pins 19 and 1) for updated part numbers such as the one that's installed is NOT done. Could this be the only cause of my woes? Adrian says that the symptoms of not having done the modification are that blowers might not work, flapper valves mis-functioning, etc. No mention of that little fan staying on or the unit staying powered.

I checked and replaced/swapped both relays in the front central electric box as well as the one in the engine compartment. I also checked the function of the NTC thermistor in the rear blower duct after the fan.

The rear blower seems to function correctly. Heater controls turned to heat cause the blower to turn on, as should be the case.
edit...Also, when I disconnect the NTC thermistor in the rear blower duct , the rear blower turns on when the ignition is turned off. Loren pointed out below, that my original idea was inverse (I was tired when I wrote the original post). NTC thermistor should read low at high temperature, so the system must think that the thermistor is failed or disconnected (as it is because I temporarily disconnected it to test) so it turns on the blower to cool, assuming the temperature might be high. The thermistor itself reads ~ 9k when nearly room temperature, and goes down when I subject it to my 37 deg C body temperature. ...unedit

The front oil cooler fan seems to work properly. Oil temperatures seem to stay at or below 9 o'clock in traffic and I hear it turn on occasionally.

This evening, I removed the CCU, cleaned out the lint and gunk from the little fan's airway tube, thermistor and blades. I also delved a bit further and took the metal shroud off of the unit only to find a couple of cracked solder joints which I promptly re-soldered. One of the bad solder joints was on a lead from the internal relay inside the CCU.

All of this to no avail. Everything works fine, except that blasted fan just keeps on running, and running and running just like that Energizer bunny on the commercials. It seems like a relay (or transistor/FET?) is stuck in the "on" position, keeping the unit powered and draining the poor battery.

I'm perfectly willing to open the unit back up and doing more troubleshooting, re-soldering, and component replacement. My last resort is to buy a new/rebuilt/or repair exchange of the unit itself.

Thanks for hearing me out, and a special thanks for those of you that go perform my little experiment with the lights still working with the car off for some time.

Cheers!

------------------------------------
1990 C4
RUF suspension kit
New "G-Pipe"
Silly chromed design 90's waiting to be replaced.

JasonAndreas

Open up the CCU again and take a look at T1 (BC337) near the relay on the PCB.

John Boggiano

None of the lights work the moment the key is removed.

Lorenfb

"Also, when I disconnect the NTC thermistor in the rear blower duct simulating high temperature ( i.e. NTC = Negative Temperature Coefficient so open circuit = infinite temperature"

Actually, an open circuit with a NTC device indicates a very low temp.

Toddimus

Thanks folks!

@Jason, I'll have a look at T1 (BC337) this evening.

@John, thanks for the check. I figured that was the case. It just confirms my thoughts. Does the little fan still run for the prescribed 15-20 minutes?

@Loren, you're absolutely right! It was late when I was typing that post. My brain wasn't working right and my basic logic failed me. NTC should mean that as temp goes up, resistance goes down. My guess is that when I disconnected the NTC device, the system logs that as a fault of the sensor and assumes the temp is high and for safety's sake turns the blower on to cool for 15 minutes.

I'll let you know how it all works out. If anybody else has ideas, I'm all ears.
I'm still hoping for that $0 fix!!

Cheers

OUR9II

Toddimus,

This is an excellent and thoroughly described technical thread. Bravo.

I too have issues with my CCU in that it does not send a return (to cold) signal to the two solenoids for the heating and cooling flappers, and the "pot" for the fan speed has an intermittent on/off feature. Driving over bumps will set the fan on or off (thus freeing the operator of the task).

I rigged a reversing momentary DPDT with a 9V battery in a little project box, connected to two spare solenoid connectors, for manual control of the flappers. Admittedly, rather Rube Goldbergesque, but effective, and is only used in the short Florida winters.

This is of no help to you (Oh by the way, no lights on my CCU buttons after shutdown), but your post has inspired me to open the box and inspect for obvious opens. My plan has been to send the unit to Loren for inspection and repair, but that will have to wait for a bit as I am selling my New Port Richey, FL home and buying a new house. <Shameless plug>

I'm not hijacking your thread, only mentioning that Loren is a Forum-trusted source if you need to service the CCU.

Good luck and keep us posted!

Lorenfb

The 964/993 CCUs are one of the most reliable ECUs and rarely fail with
the exception of the problem described in this thread and here:
www.systemsc.com/failuremodes.htm

Most CCU system problems relate to the servo units and occasionally to the wiring.
That's why proper diagnosis, other than the typical failures, requires use of the
Porsche Hammer/PST2.

Bottom line: Avoid concluding that your CCU is bad without a thorough diagnosis.

John Boggiano

Yep.

Toddimus

Well, I can't say exactly what was the culprit because I did a bunch of things at once.

DISCLAIMER!! If you try to do this and fry your car, don't blame me!! There's always potential to screw something up, short a lead, sloppy solder, etc.

I took out the CCU again, and de-soldered the headers that connect the two boards. Man that's quite a job! De-soldering copper braided tape to the rescue. First, I had hoped that I'd find something inside that I hadn't seen before. No dice.

Then I checked T1 which is next to the internal relay. Solder points looked fine. I'm pretty sure it's a transistor, because it has an "E" (for emitter?) next to one of the pins. It showed a reading of .95 across two of the pins with the meter set on diode setting, just like another same part on the board. Not
conclusive, but I think it is fine.

Next a second re-solder of all questionable solder points, including the ones for the relay and T1 for good measure. Clean up solder flux with at toothbrush and alcohol.

Solder the boards back together with the headers. Clean again with alcohol and toothbrush.

Now, for the thing that I think really fixed it...

I soldered a bit of wire between the board solder points for pins 1 and 19 on the 35 pin connector. I made it long enough so that the wire loop could be passed outside the metal chassis and be cut and insulated if it didn't work. The reason I chose to do this is that in Adrian's book, he suggested that if the CCU was replaced with a newer unit, a wire-mod is sometimes necessary for it to function properly. The CCU is p/n 964.659.047.01 (fitted to later cars?), which in a table inside Adrian's book, is one that is necessary to perform the wire mod for proper functioning in 89-90 cars. I think I remember the previous owner of this car saying he had purchased a new CCU for ~$1000. I guess this would explain some things: the later part number and the lack of wire-mod by an un-knowing mechanic.

The first time I turned on the ignition everything seems to work fine, blowers, flapper servos, etc. Turn off the ignition, keys out, and the little fan stays on (like we should expect for 15-20 minutes), lights on the buttons still illuminate (weird, but maybe ok?), and I hear a single click every 11 seconds indefinitely. Sounds like the relay engaging, waiting 11 seconds, then disengaging, wait 11 sec., engage, etc... ad infinitum so I leave it for 30 minutes.

I go back to the car and everything's quiet, no fan, no clicking, no lights on the buttons. YESSSSSS!!!!!!!! FIXED!!!!? Turn car on, try everything on the CCU successfully, and turn the car off for the definitive proof: "once is usually, twice is always" test. Fan on, but no relay clicking this time. Lights do still work.

Go back inside, read some rennlist posts about the airflow meter and downhill power loss (great read by the way!!).

45 minutes later I go outside to check again and all's quiet on the CCU front.

I pat myself on the back, happy with my $0 fix and proceed to write this post.

Thanks for all of your help folks!

Toddimus

I don't know what happened, but it seems like it's back to its old tricks.
Hmmmm....

I might just have to go yet even deeper into troubleshooting. I figure that in the end, my last resort is to find a repaired unit, or maybe send mine in to get repaired. Maybe even to Loren? You fix these things don't you? You give me a good deal?

Toddimus

Another Rennlist success story...

Sorry to bump my own thread, but this may be of interest to those of you with the battery drain - little fan running problem.

So I decided to try JasonAndreas's suggestion and replace T1, which is a NPN transistor (p/n BC337). Instead of ordering the exact part from Digikey for $0.14, I went to Radio Shack on the way home and bought a 2N4401 transistor for $0.69 (way over priced!!!). This transistor had similar characteristics as the BC337 part, so I thought I'd give it a shot, seeing as though the function of the transistor is just a switch for the internal relay.

After checking out the pin mappings of the two parts, I noticed that they were oriented in opposite mechanical positioning. Three pins 1-2-3 with the flat side up were opposite on the new part. Carefully noting the new and old orientations, and not even needing to de-solder the two boards apart, I de-soldered the three pins of the old transistor and soldered in the new one.

In 10 minutes I had the CCU back in the car to test. The car wasn't too hot, so when I started it and quickly turned it back off again, the little fan and the depressed recirculation button light turned off after about 5 seconds. I could hear the internal relay make a click as it turned off. Sounds like success to me, but I had been thwarted previously, so I went for a more in depth test.

As I understand, the CCU system allows for the engine bay temperature to be monitored for 20 minutes if upon shutting down, the NTC thermistor in the rear blower duct shows a high temperature. On to the test...

I let the car idle for about 5 minutes to heat up, then turned it off. The little fan stayed on for a bit, along with the little light of the depressed buttons on the CCU, so I helped the CCU think the engine was still too hot by giving the blower duct thermistor some 98.6 degree body heat. The little fan and the lights stayed on for exactly 19 minutes and 35 seconds, then turned off with a click of the relay inside the CCU.

Once is usually, twice is always, and three times is... uh... success. I just tested it again and it turned off after about 10 seconds.

NOW I think I can chalk this one up to a victory!!!!!!!!!!!!! Of course, Murphy's law usually applies in situations like this, but I think I've got him beat this time.

Remember, BE CAREFUL if you decide to try this yourself. I can't be held responsible for any damage you may cause to your car, yourself or even your pocketbook by attempting this surgery! Also, sorry to the folks who make a living fixing these tempermental units! I figured if I broke it then I'd find a second-hand unit, or bite the bullet and buy a new one. Turned out to be a 69 cent fix!

A big thanks to all who contributed to the posts that led me to this outcome, especially JasonAndreas who hit the nail on the head with his suggestion.

Case closed!

JasonAndreas

That makes at least two of us now that owe a beer to Marc Geyskens.

Toddimus

Is Marc on this forum? If you're there, thanks a whole bunch!! It worked wonderfully!

Laurence Gibbs

Useful tip: don't test the transistor in circuit, it's likely to be connnected to other things which will confuse the reading. Remove it if poss or de solder two pins and take readings from the pins. in general (over simplifying) NPN transitor such as bc337 should be lowish ohms forward biased B-E i.e. reading with your multimeter on ohms red lead on Base connection black lead on Emmiter and open circuit or very high ohms when lead connections reversed. E-C should be open circuit (though some transistors have a diode so can read one way!) In general readings in both directions or open circuit readings in both directions signify a failure. Please accept the over simplification.

pncarrerars

This ccu problem sounds just like the one that I have. I have purchased a BC337-16 replacement but cant work out how to tell if it is a direct replacement or needs turning round. Some BC337 seem to have pinout 1-E 2-B 3-C & some are 1-C 2-B 3-E. Is there any form of marking to look for or electrical test that I can do. I have tried Laurences check on the new one but cant tell which is C & which is E

Pete