Heirsh

Does anyone know a way to check if this part is dead? It looks a bit old, but I dont see any fry marks. I thought my problem was my CCU, but I sent it off to Otto and he said it was fine. He recommended I check the relays and this part.

Just in case anyone wants to help with troubleshooting here are the details.

-No fan function from CCU. Not defrost, not regular ventilation fan. I do not know about the oil cooler fan.
-A/C compressor engages when buttons for AC and defrost are pressed..
-Jumpered fans to 12v per Adrian's troubleshooting. Both regular ventilation fan and Oil cooler fan function and sound fine
.
-So I figured the CCU. Sent it off to Otto and he said it was fine.
-I do not know if I checked the relays. I don't think I did since I can't get any blower functionality. I'll go pull them now and check them.

Peter_964C2

I have exactly the same problem, and it is still not solved.
Via a local shop (2nd hand) I was able to try solving the problem by replacing the Final Stage Ampiflier and the CCU, but it didn't solve the problem.

The next step will be replacing the Registor and the PTE on the rear fan (motor compartiment). My rear blower is not function as well.

Please post any results here, I can use them ;-)

Regards
Peter

MA7008O

What is that part and which is it's funtion anyway?

Peter_964C2

The CCU (this is the part inside the cockpit with the buttons to operate the heater/airco, .. ) doesn't have a "strong" output to the blowers.

The Final Stage Ampliflier is between the CCU and the front blowers.
His function is to amplifly the signals coming from the CCU.
It accept a low power signal and ampliflies it to a signal strong enough for the blowers. It is mounted on a aluminum plate for cooling.

sorry for my English.. it's not easy ;-)

..Peter

MA7008O

OK, thanks for the explanation.

Heirsh

I guess I should be able to read a varying voltage coming into this unit and it should spit out varying voltage. Anyone have the schematic of which leads go where?

Peter_964C2

This is probably not clear ..
But if you want, I can send a better quality schematic via mail..
or is there another way ??

Heirsh

Thank you so much for the wiring diagram. I have to get ahold of a set of manuals or a cd-rom version.

I found my problem. Fuse 28.

The fuse was fine (one of the first things i checked), it was its holder. I bent the ends of the fuse to make better contact with the widened female end and it works. I'll have to actually fix it another day, for now I'm going off to celebrate.

Ah the joys of actually finding easy solutions to seemingly complex problems.

may the trend continue.

Lorenfb

The 964/993 CCU ECUs are very reliable and rarely fail with the exception of the
suction fan turn-off problem.

Check out here ( www.systemsc.com/failuremodes.htm ) under Climate Control Typical Failure Modes.

The most common CCU related problems are:
1. bad actuators, e.g. mixed flaps, air diverters, & etc.
2. bad relays
3. bad rear air temp sensor or its connection
4. bad thermal resistor or its contacts
5. bad fuses or their connections

Before assuming a bad CCU ECU, its fault codes must be read.
This will usually greatly help to diagnose the system problem.

Peter_964C2

My problem is stil not solved yet.
The CCU and the Final Stage is ok.
Fuse is ok, wires not checked but seems to be ok.

The front blowers and the rear blower are not working.
I could let the blow with a bypass.
If the PTE and the Registor is broken, will the blowers run ?

Lorenfb

"The front blowers and the rear blower are not working."

The front blowers will not work if the rear blowers don't work AND the temp ****
is set to heat. The front blowers should work when the temp **** is set to cold,
though. The final stage gets its main +12 volts from the ignition switch Term X
(G29 on the CCU) & fuse 17. Without this power, the front blowers won't run.
Term X position is the accessory position (1st before "run" position).

Peter_964C2

This could be the cause of my problem !! the ignition switch !!
If the ingnition switch is at the last position, when I "touch" the ignition switch, I hear a relais clicking. The ignition switch may be bad.

I found this in my books, but I have problems to read this picture.
Can somebody explain what happens in the different steps of the ignition switch?

Lorenfb

position 0 - key out
position 1 - accessory mode
position 2 - run mode
position 3 - cranking mode,

P power @ position 0
R power @ positions 1, 2, 3
X power @ positions 1, 2
15 power @ positions 2, 3
50 power @ position 3
30 is battery power to ignition switch

The diagonal lines denote the wiper of the ignition switch which moves as the key
is turned.

Peter_964C2

Ok, now it is clear :-)
I know what to do this evening!

Thanks Loren

Scott Dunavant

This post just helped me. I deleted my rear defrost with a 993 RS rear Glass. But that fuse 28 works the blower motor. Many Thanks