gmorat

So I used Scantool version 4 and Tores T-ODB hardware and I got an error code on the CCU.

Error code CCU 43 Rear blower motor speed 1

I found this on Tores site.....

Fan speed is controlled by a relay in the left electronic unit in the engine compartment, (see picture) and low speed is done by switching a series resistor/ballast with the motor, similar to the oil cooler/A/C condenser fans, and uses the same relay type. The low speed resistor (#964 616 550 02) is mounted on the air duct beneath the fan housing for cooling, and it contains a thermoswitch for resistor overheat detection. This is done to protect the resistor and possible engine fire if the fan seizes or short-circuits. This thermoswitch can fail over time and disconnect the resistor, thus no low fan speed. There seem to be a method of resetting the thermoswitch, have a look at the pictures or on this thread on Rennlist. I always change a failed resistor.
The AUX/rear fan relay has been seen to fail due to excessive current, often caused by a seized or damaged fan motor. Test the relay by removing it and short terminals 30 and 87 to start the fan at high speed, and short terminals 30C and 87C for low fan speed. See the relay underside for terminal ID's. Test the CCU control signals to the relay by measuring on terminal 85 and 85C. These will be grounded by the CCU at high and low speed accordingly. (plus on terminal 86)

The CCU supervises the rear fan operation by a feedback signal. If the fan is seized, resistor is faulty or its fuse blown, the CCU will produce a OBD fault code, and stop the front fans intermittently if the temperature control is turned up and heated air is needed. The defroster fan operation will also cut out shortly after starting due to the max heat setting. CCU connector G19 and G1 are the blower motor supply voltage feedbacks. In case of using a "RS duct" modification and rear fan delete, you will have to fool the CCU into thinking that the fan motor is OK in order to avoid the front fans to shut down. The simplest method to do this is to connect switched +12V to the rear fan terminal 87. (the relay can of course be removed)

The main thing I wanted to know is how exactly do you 'short' two terminals like in the description? As soon as I know if its the relay, the resistor, the fan or the fuse I'll be able to get this sorted. I actually don't think its the fan as the fan definitely seems to be working Whether it operates at 2 distinct speeds is hard to gauge. If it does the speed and noise from the fan are hard to discern to me. The fan is on but makes around the same level of noise regardless of the fan speed selected on the CCU.

Thanks

G

P.S I am having the driveblock problem with the scantool software and the T-ODB also whereby the Motronic selection never seems to connect but all of the other modules do. I need to try some workarounds from the troubleshooting guide.

Also, I get a numbered error through the software but its doesn't give the written description. I have selected 993 in the config file repeatedly as well as ensure that the trouble_code.txt is identical to the 993 trouble code test manually. Not sure why its isn't working.

Tom T.

I use a home made 6 inch 12AWG wire with a fuse installed and a male crimp style terminals on each end. These items can be purchased at a hardware or auto store. Or you can buy a pre-made test wire kit. Whichever you choose you would insert one of the male terminals into the correct relay location and the other test terminal into the corresponding relay location to close the circuit. So to test the fan's high speed per the description you quoted, first remove the correct relay from the panel, insert the test wire into terminal 87, then carefully insert the other end into terminal 30 (terminal 30 is wired to the battery). You should hear the high speed fan. Repeat the same test for low speed using terminals 30C and 87C.

gmorat

Thanks! What would they be called do you know, I've searched a bit and can't seem to find something that matches your description. Can't see myself making one if I'm being honest.

Thks

G

JB 911

G, it sounds way harder than it is. Basically it is the same test that Bruce7 does for his ac and oil cooler fan resistors - just in the back for rear engine fan one. He doesn't cover that one, but you are doing exactly the same test back there. Check out part 1 pics for the jumper.

https://rennlist.com/forums/993-foru...resistors.html

gmorat

Awesome, no need for a fuse on it then?

Even I can make this!

G

JB 911

I had no qualms just testing fan operation without a fuse, but given your ccu gremlins, I would put a fuse in there. I'm sure you will find what you need right next to the other parts you need on the same aisle at the auto store.

gmorat

Am I just putting a standard automotive fuse with the wire connected to each of the terminals and then terminating in the crimp on spade ends? Does it matter what amp?

G

JB 911

I bet if you go poking around at your local autoparts store you'll find something like this. Maybe at radio shack too, but then it would be $19.99

gmorat

Ordered! Thats is awesome. Cheers!

G

Jonttt

I had the same problem last year, hope this helps....taken from my journal http://911uk.com/viewtopic.php?p=844606#844606 ...................

Ps I used a bosche hammer diagnostic tool which just presents the errors as narrative and allows easier control of the systems for testing ;-)

I have one fault left on my car to resolve and today was the day to fix it ! ......



Research into this proved frustrating and time consuming.

Whenever I work on a problem I like to fully understand what the problem is, why and the best way of fixing it.Google is a great tool but the problem is that when you are searching many years of internet information (mainly forum based in this context) often that information is out of date, not comprehensive and sometimes just plain wrong. The working of the rear blower of a 993 falls into that catagory (not least becasue it has two seperate functions). There are endless forum threads discussing when/how/why it should operate, how to diagnose / resolve problems etc..... but no one comprehensive, clear source of information.

It was also evident in my search that there had been a major issue with part of the system when fitted to the earlier 964 cars which resulted in major engine fires, warranty recalls and a new upgraded replacement part being fitted (and later used in the 993) ie there was a danger that not understanding what you were doing could result in an engine fire !

I was therefore keen to not only understand how the rear blower should function both as part of the cars Climate Control System and its other role to provide additional engine cooling.

In my search I have picked bits and pieces up from many sources. I have often forgotten where to be honest as when I started I did not think the search would take such a convaluted route. However there was one main source of base information which proved invaluable which was Tore's excellent 993 HVAC reference site:

http://www.bergvillfx.com/porschehvac2.html

However even here I found the explanation of the rear blower function confusing until I got my head around the system when linked to other sources.

So I used this as a base to (hopefully) give a more comprehensive and easy to understand explanation of the 993 Rear Blower functions, common faults and how to diagnose / fix them..........


*********************************************************
Rear (AUX) fan / Blower Motor purpose / operation and fault Diagnosis.........

The rear fan(s) has two purposes. (nb Turbo models have two rear fans):

1) To HEAT the cabin ie help blowing air through the heat exchangers onward to the front fans to improve the heating of the cabin.

The fan run at two speeds, and typically starts at mid temperature setting on the CCU (climate control unit on the front dashboard). The fan will run on low speed if the fan speed **** on the CCU is below 2. Fan settings above 2 will set the rear fan speed to high. Remember, the operation of the fan is also dependent on the temperature setting, i.e. if it's set to minimum, the rear fan will not start since no heated air is needed to the cabin. However, even on minimum temp setting, the rear fan could automatically be started by its secondary engine cooling function (see 2. next).

2) To COOL the engine / heat exchangers in two circumstances:

a) when the ignition is on and the CCU temperature **** is set to minimum and mixer servo flaps are closed ie min heat setting on CCU. The CCU supervises the engine/air duct temperature with a temperature sensor and runs the rear fan if needed:

- fan at low speed (40-45degC)
- Fan at high(62-57degC)

b) at ignition off by blowing the heated air out through two spring loaded dump valves under the engine. The mixer flaps closes to enable the fan to build up enough air pressure to open the dump valves.

- Fan at low speed if the air duct temperature is above 75degC, and shall stop when below 70degC.

The maximum fan run time at ignition off is 20 minutes. If the fan does not stop you might have a problem with the temperature sensor or the fan relay.



The Rear Blower Fan is controlled (powered) by a relay in the left electronic unit in the engine compartment.

The Low speed is done by switching a resistor (ballast) fitted in series with Relay and Fan motor.
This low speed resistor is mounted on the air duct beneath the fan housing to keep it cool (resistors get very hot so locating in the airflow helps to stop it overheating without having to fit heatsinks etc....), and it contains a thermoswitch for resistor overheat detection. This is done to protect the resistor and possible engine fire if the fan seizes or short-circuits.
This thermoswitch can fail over time and disconnect the resistor, thus no low fan speed. (part no. 964 616 550 02 nb the earlier part ending 00 did not have the thermoswitch to protect it and hence was a factory recall item!!!!! All 993's had the safer 02 part fitted)

Part 10 on this PET extract..






There is a method of resetting the thermoswitch but I would not recommend doing this however as the part is cheap (c£25) and the risk of the thermoswitch failing and an engine fire resulting is not worth it IMHO.
Nb make sure it is cool before attempting to replace it as it can get very hot! Also these MUST be fitted properly and secured ie if it comes loose it can cause an engine fire !!!!

Because of this some people us an additional Tie Wrap to secure in place ;-)
nb I found the mounting springs on the new part secured it much better than I had read so this may be more a factor of how the plastic it mounts on is worn or not ?








The AUX/rear fan relay has been seen to fail due to excessive current, often caused by a seized or damaged fan motor. If the relay has failed the fan will either run permanently or not run at either low or high speed. If the fault is low speed fan failure only the fault will be with the low speed resistor and not the fan relay.

You can test the relay by removing it and either:

- swapping with either the oil cooler or air con condensor relays which are the same, or

- short terminals 30 and 87 to start the fan at high speed, and short terminals 30C and 87C for low fan speed. See the relay underside for terminal ID's.

Test the CCU control signals to the relay by measuring on terminal 85 and 85C. These will be grounded by the CCU at high and low speed accordingly. (plus on terminal 86)

The CCU supervises the rear fan operation by a feedback signal. If the fan is seized, resistor is faulty or its fuse blown, the CCU will produce a OBD fault code, and stop the front fans intermittently if the temperature control is turned up and heated air is needed. The defroster fan operation will also cut out shortly after starting due to the max heat setting.

CCU connector G19 and G1 are the blower motor supply voltage feedbacks.

In case of using a "RS duct" modification and rear fan delete, you will have to fool the CCU into thinking that the fan motor is OK in order to avoid the front fans to shut down. The simplest method to do this is to connect switched +12V to the rear fan terminal 87. (the relay can of course be removed)

***********************************************************


This is the original 964 USA market recall for earlier resistors which did not have the thermoswitch to protect the resistor from overheating:

AFTER THE ENGINE HAS BEEN TURNED OFF, THE REAR HEATER WILL AUTOMATICALLY OPERATE IN ORDER TO DISSIPATE HEAT IN THE ENGINE HEATING SYSTEM. DURING THIS OPERATION, THE RESISTOR FOR THE REAR HEATER BLOWER CAN BECOME OVERLOADED DUE TO A BINDING OR SEIZED REAR HEATER BLOWER. THE OVERLOADED RESISTOR CAN CREATE HEAT SUFFICIENT TO IGNITE THE PLASTIC AIR PIPE TO WHICH IT IS CONNECTED, RESULTING IN AN ENGINE COMPARTMENT FIRE. PORSCHE DEALERS WILL INSTALL A NEW RESISTOR CONTAINING A CIRCUIT BREAKER FREE OF CHARGE.

Vehicles affected:

1989 PORSCHE 911
1989 PORSCHE CARRERA
1990 PORSCHE 911
1990 PORSCHE CARRERA
1991 PORSCHE 911
1991 PORSCHE CARRERA
1992 PORSCHE 911
1992 PORSCHE CARRERA

*************************************************************

So now I understand how the Rear Blower should work I can easily identify that the low speed mode fault must be the resistor which has either failed or the thermoswitch has been activated. In either case I need to fit a new resistor. Fortunately this is cheap (c£25 incl VAT) and easy to fit. Whilst at it I decided in a fit of OCD (preventative measure) to also replace the temperature sensor which is another common part to fail with age (similar price and even easier to fit).

Its always nice to get new parts .......




Rear Blower Resistor with built in thermal switch....




I have ringed the spring clamps which hold it in place when fitted...





Rear Blower Temperature Probe





It is easy to see the temperature probe fitting when looking at the left hand side of the engine bay. The resisitor is tucked down the side but pretty easy to get at....







I decided to tackle the temperature probe first, simply pull off the electrical connector....




and then pull the probe out of the rubber mounting (nb a bit of a tug is needed as its held in by a rubber ridge)....




old and new side by side. As the old one was not actually faulty I'll keep it in my parts bin ;-)





fitting is simply the reversal but can be frustrating as you have to push the edge of the probe into the rubber mounting to the retaining ridge. As you are pushing against rubber you have no leverage. I found it best to try to get one edge in the ridge and then rotate the probe until it all slides into place....

part of the probe in place....




rotated and all in place ready to have the electrical connector pushed back on....





Now onto the resistor......

nb. Please remember to do this with a cold engine as the resistor could be very very hot if its been in use!

It pulls free by just levering away from the mounting




It is best to pull it up with the electrical spade connectors still in place as its easier to then pull them off. They do require a bit of force as they have probably been in place for many years. The wires are colour coded so its easy to remember which goes on which connector.....




Fitting the new part is simple reversal of process, push the spade connectors on, clip into the hole from which you removed it.


So job done in a total of a couple of minutes :-)



Now for the testing to see if its works properly and the fault codes are gone.......

I'll be using my Bosch "Hammer" again for this. One of the main advantages of this piece of kit is that the lead to the diagnostic port is long enough to reach the rear of the car so you can see what you are doing when testing the part and you can switch parts like this on/off at the touch of a button.

I start by turning on the unit to clear the existing fault code....
















I then connect up the diagnostic lead and run a new full systems diagnostic and check for any faults. Fingers crossed there should be none....








So job done and fault fixed.......

but I decided to see the results of my labour in action.


So first what does the Rear Temp Sensor actually read






Next I wanted to see the rear Fan Blower working in both low and high speed setting......

As the sound of the fan running at two speeds is what I wanted I decided to take a video. Click on the picture below to link to the video




So there you have it. Not only have I fixed a common, easy to fix, problem for myself but more importantly to me I have a much better understanding of how part of my car should work and why ;-)

JB 911

Excellent post jonttt thanks for sharing.

Seems with a helper to adjust the fan speed on cue while you monitor the engine fan one should be able to verify the two speed operation with this simple test? On high you should be able to feel the air coming out of the flaps under the engine too, or is that going to be dependent on engine temp too?

"The fan run at two speeds, and typically starts at mid temperature setting on the CCU (climate control unit on the front dashboard). The fan will run on low speed if the fan speed **** on the CCU is below 2. Fan settings above 2 will set the rear fan speed to high. Remember, the operation of the fan is also dependent on the temperature setting, i.e. if it's set to minimum, the rear fan will not start since no heated air is needed to the cabin. However, even on minimum temp setting, the rear fan could automatically be started by its secondary engine cooling function (see 2. next).
"

gmorat

Stunning info!

I'll order the parts. I definitely have the fan working at high speed but not low speed. The difference is so obvious in your video. I thought maybe it was subtle but not at all.

G

gmorat

Just confirmed with shorting the relay and nothing on the low speed but the high speed works just fine. I guess I need a new resistor. I was walking away from the car after a bit of a drive and I heard a high pitched whining coming from the back of the car.

It could be the fan bearing itself or the motor belt-tension sensor. Whats the best way to figure it out?

Wasn't a one to one with the blower so...........then again maybe it just stopped whining after a minute or two.

gmorat

All done and no codes. Thought I'd broken something for a bit as when I went to test the fans by shorting the terminals and I got nothing. No fan of any speed.

Turns out the 15amp in-line fuse wasn't big enough and kept blowing. I put a 30amp in and I got both speeds on the fan.

Only problem now is that the spring clip from the temp sensor fell into the engine bay.

The lead seems tight enough without it but it's a little frustrating. No sign of it anywhere I'm afraid. A sacrifice to the great air-cooled god.

Didn't notice the spring clip on the photo of the clip that was posted with the how-to.

Thanks all, it's been 3 months since my CCU blew up and it's great to be back to a state of everything working as it should.

My resistor was a dried up brittle mess, hard to know if the temp sensor was shot or not but I replaced it anyway. Bitch of a time getting the temp sensor back into its hole. Wiped the hole with a little silicone spray on a shop towel which helped in the end.

G

Jonttt

Good to know you got it sorted