Stephen Koch

hi,

i have CCU error codes

12=Left mixing chamber temperature sensor
41=Condenser blower motor
43=Rear blower motor speed 1
46=Rear blower motor speed 1
44=Rear blower motor speed 2
47=Rear blower motor speed 2

I cleared them and went for a drive and still get the same error codes. It sounds like the rear blower motor has a problem as the blower resistor only affects one of the speeds. I've checked the fuse and it is fine, I've removed the rear blower motor and taken it out of the plastic housing, i can spin the fan by hand so it isnt seized. Is it worth doing any more testing/checking or have i done enough to confirm the blower motor needs to be replaced? i have a fairly weak air coming out of the vents so assuming the blower motor is contributing to that.

The AC condensor blower motor is new (less than 1 year) however i think i have a refrigerant leak, does that cause error code 41?

One last question if i need to replace the rear blower motor is it worth paying the extra to move to the 993 blower motor or jkust replace the bosch unit in the 964 housing?

thanks
Stephen

ToreB

If fuse and motor are OK, I would inspect the fan relay. Is it properly seated, or even present? It is (should be) placed in the rear fuse box.
You could try to pop off the lid of the relay and manually depress the high and low speed relays to see if the fan works.
This relay is the same type as the oil cooler and condenser fan relays, you could try one of these in the rear fan relay position.
Depending on the type of diag tool you are using and the CCU version, you will be able to activate the rear fan relay outputs via OBD diagnosis.

Without a working mixer chamber sensor you will never get proper temperature regulation. It is possible to change the thermistor sensor, see here.
Cheers,
Tore

Stephen Koch

ToreB

I would suggest to do proper testing of the rear fan circuitry before starting to change parts. My DIY page show you how.
Non working fan low speed is most probably due to a defective low speed resistor.
Cheers,
Tore

power_up

Is your main problem low/weak air flow from dash vent? If so, start from those five servo probably fresh air servo first.

Stephen Koch

Bearing in mind this is my first 964 and I’ve only had it 2 years and suspect these were there from the start so not sure what normal looks like.

What i think my issues are
- no real flow from passenger side vents (i assume this is servo)
- at setting 1 on the fan flow feels very low across the temperature range. (Sounds like blower fan is at least not working in low setting)
- aircon isn't working (i think i have a leak, i just had condenser replaced so hopefully not that)
- at times the airflow stops on higher speeds (2 and 3) like it turns off for 1 second or less and then comes back on again (not sure am wondering if the blower motor is intermittently getting stuck).

I was going to try and fix blower first just because i’ve taken it all apart at least once so know how everything fits together now!
Stephen

Stephen Koch

Hi,

i have replaced the rear blower motor resister, replaced the relay and soldered in a new temperature chamber sensor with the replacement kit. All of my error codes have now been cleared and are not reoccurring, which is good news.

i still only have air coming from the drivers vents, not the passenger vents. Looking at the diy diagnosis on the bergvill site the most common cause is sticking servos. I have checked servos and 2 and 4 and both are moving correctly when i change the temperature.

The fuses are okay, is the next thing to check the front blower motor? How can i tell if it is running? Is there a way without taking the cover off? It seems like a lot of work to remove it so want to make sure i’m reasonably sure it is the problem. Is there anything else i should check first?

galanevans

I'm glad to see you got to the resistor. I was having several of the same error codes and the fan speed was stuck on level 2...that seemed to do the trick for me. Good luck w/ the balance of work.

ToreB

You can hear the front blowers running if they do. The blower housing cover is possible to pull off, you have to remove the metal clips holding it first. Have a magnet picker ready, the clips have a tendency to fly off when dismantled.
Cheers,
Tore

Stephen Koch

Ok thanks will try that next. Does everything run with the engine off? I've been testing it with the engine running and hard to hear anything over the engine.

ToreB

All fans operate with ignition on, engine running or not.
Cheers,
Tore

Stephen Koch

Thanks Tore. Do you have a view on replacement parts for the front blower? In UK i seem to have options for Dansk, Retroline or OEM. Would likely go for dansk, do you have a view? I’ve looked at rennlist and in the US they have URE which seems to be okay as a replacement though there isnt a lot of evidence one way or other on longevity,

jwbavalon

Stephen, you mentioned that the codes might have been there be there from the start. Is there a possibility that the CCU was exchanged at some point? If a later CCU is installed in a '89 or '90 without the wiring jumper fix, you will get your 43-47 codes. I see from the scan, you have a CCU with a 993 part number. Tore might be able to help if this is the problem.

Stephen Koch

Thanks for spotting that i had noticed the part number of a 993 on the scanner, but hadnt seen about the pin jumping. i do have a lot of documentation on the car but dont have any record of a new ccu though the records early on are missing. It is fairly easy to remove the ccu so ill try that first and check those two pins have been jumped incase that is the issue.

ToreB

I agree, a 993 CCU without modification of the rear fan feedback circuit will produce fault codes on the rear fan due to the missing feedback signal on the second feedback input.
However, only codes 46 and 47 would be stored.

If codes 43 and 44 are also stored, the rear fan circuit must be inspected.

There are a number of needed modifications of the CCU wiring if you are to use a 993 CCU in a 964, depending on the car model year and the part number of the 993 CCU. Even the official Porsche bulletin on this is incomplete.
Cheers,
Tore