stu.p

My heater blower is not working on a 1990 964 i currently have.After a quick check only,I removed and tested the rear fan and with 12volts powered out within the car it operates fine although when in car and plugged in, it does not operate so further investigation required and ideas welcome??.....I believe that the front fans dont work because the rear does not,,hence no blowers at all work at present!

Strange thing is aswell,,,after quick check i am pretty sure i can hear the oil cooling fan coming on when i press the left hand side button on the climate control unit(this button i believe is the quick defrost and should be nothing to do with the oil cooler fan).
has anyone else came across this strange behaviour??

When pressing left hand button

boxsey911

As a first check, how's your 30 amp fuse in the rear fuse box?

jimq

Your CCU is opposite looking from mine.

stu.p

Checked 30 amp fuse in rear comp and it appeared ok when i removed and visually inspected

boxsey911

How about the 25 amp fuse (position 1) in the front fuse box?

jimq

the left hand button is for the air conditioner on mine. It should turn the left hand aircond radiator fan on.

boxsey911

and let us know if the blower (and fans) work if you turn the temperature to the blue dot (it's all the way round to the red in your pic)?

BTW the button on the left on mine is the windscreen defroster (no aircon on my CCU). It looks like yours with the little orange light but has a windscreen defroster picture on it.

stu.p

Thanks for responses guys!
Fuse in front comp was also ok,,i tried turning **** to blue dot and still no fans unfortunately??

boxsey911

From Adrian's book, a rear blower that does not run at all is caused by:

a) a blown blower fuse
b) a failed blower relay
c) a failed blower
d) a failed CCU

It looks like you have ruled out a) and c), so I would next swap the relay in the rear fuse box with the oil cooler relay in the front fuse box. They're easy to identify as they have the Audi logo on.

stu.p

Tried swapping all relays and all appear working fine...Tested them by putting each one where the oil cooler blower relay is usually situated,,press the quick defrost button and yet again on comes the oil cooler fan???.....
Something up with the defrost button switching on the oil cooler fan,nobody heard of this before??...Maybe the ccu unit at fault?? or somebody playing around with things previously,,however all wiring appears pretty original.

I have the ccu unit in my 964t which i may swap and try although it differs slightly fron the 964 c4 one it may still work.

boxsey911

Stu, I'm guessing from your last post that you've only just got this 964 and just found that the HVAC system is not working? With having a 964T aswell I'm sure you know your way around these cars and it therefore makes me wonder if the PO of the C4 had HVAC problems for a while and put a CCU in that is not appropriate for the car? As you know, there are quite a few variations of the CCU depending on year, RHD, LHD, A/C, etc.

Turning on the oil cooler via the CCU is indeed a strange effect. Is the O/C relay in the correct slot - R4 on the fuse board?

It might be worth pulling your CCU and checking the part number against your VIN number at your local Porsche Centre parts counter.

stu.p

Steve,,yeah knew blowers werent working when got car and just trying to resolve now,,I can get by with electrical work but mechanical work more my thing!!
Yeah oil cooler relay in correct slot and as soon as you remove it the fan in the o/c stops turning when the defrost button is on within the ccu unit!
Good point,could have be a previous attempt to fix with wrong replacement unit hence still not working and all sorts strange now going on!.

The resistor near base of the rear blower pipe i noticed is updated one with newer part number however if this was faulty or the temp sensor in same heater pipe was,,could this give me issues with blowers not operating at all?

Think will maybe remove unit tonight if get a chance!

boxsey911

The temp sensor and the ballast resistor in the blower ducting are not known for stopping the blower running. Conversely, a bad temperature sensor is known for making the blower run all the time even with the ignition off.

Having no cabin fans working can be caused by a failed final stage relay but I don't think that would stop the rear blower running at low speed. Although the CCU is linked to the oil cooler fan (involved in its control), the strange behaviour of the defrost switch turning the oil cooler fan on is (for me) pointing towards a CCU and/or wiring problem. Let us know what part number you have on the CCU and I'll check it against the list in Adrian's book.

Aswell as the many threads on here about HVAC problems, there is a good summary of the system here:

http://964uk.com/html/Tech%20-%20Heating.htm

stu.p

Excellent info Steve and much appreciated!
Will remove and investigate ccu tomorrow!
cheers!
Stuart

stu.p

Stripped ccu unit today and could not see anything obvious wrong however when removing the unit and moving it around in the rear area of the unit i briefly heard the rear fan come on although could still not get the front fans to work whilst rear fan was running!
After cleaned ccu unit with elec spray and re-assembled now the oil cooler fan stays on all the time when the ignition is on and fans still do not operate!

Steve i do not think unit has been removed before however you never know,,the unit number is 96465904600

Do you Steve or anyone know of any units for sale or name of company in uk who refurbs and cost?

Thanks in advance!