Yet another person with a windscreen demister / fan heater fault

[Guest]

[] Rrrrraaaaggghhhh. Why oh why build a car that cost nearly 60k new with such a temperamental and poor quality windscreen demister? Very unsafe and uncomfortable.....especially with the windows down on the motorway in 2 degrees centigrade wather!
I just wish my dream car could have been a 350z or a celica t sport....but the 964 is so lush to look at i had to have one.

It went the day after i aquired it. With the ingnition turned on and the engine off ....there's not a whisper from the fans at all.
I've checked the fuses under the luggage compartment bonnet.
I believe there's also a fuse / relay box inside the engine compartment to check too.....is it easy to find?
Hopefully tomorrow (sunday) will be sunny and dry so i can have a butchers and try to fix the annoyance!
I have to use the car daily at the moment....love driving it , but new things crop up all the time...today on my way home from shopping in swansea (wow ...the rock and roll life i lead!!) the engine developed a whining noise...what the hells all that about?
its a 1991 C2 911 964 (with RS bits all over the shop!)
Thanks to anyone who can be bothered to talk me through the same old problems!

Glynmun...near llanelli
[:-]

 

[Dave Wilkinson]

Hi - I see you are beginning to experience the joys of 964 ownership then!!

The heater thing needs a little bit of scientific diagnosis. If you turn the fan control off and turn the heat control to the red dot with the ignition on, make sure the rear blower runs at slow speed. If it doesn't - there's your first problem. The rear electrical panel is immediately inside the engine lid, to the left hand side with a kind of triangular shaped cover help by three knurled screws. They SHOULD be hand tight and should undo quite easily. I have known them to be tightened too much and you may have trouble getting them undone. There is a fuse in there for the rear blower. Make sure the fuse is not blown or replace it with a 30 amp fuse. There is a chance the label in the lid might say 25 amp - but it should be 30 amp.

If the rear blower runs witha good fuse we're geting somewhere. If it still doesn't run you need to check the ballast resistor which is clipped into the left side of the black blower plenum tube. Later resistors had a thermal cut-out which has to be reset by pushing it.

Once the rear blower runs you need to turn your attention to the front blowers. Turn the fan setting to max (4) and see if the front blowers now run. A problem I've heard of before is that the final stage amplifiers fail (fitted under the front electrical box) and if the fuses are OK it may be that's where the problem could be.

The final cause could be a failure in the CCU itself. You want to hope it isn't that because they are expensive although they can be repaired fairly economically.

If you can get some answers to these questions we mau be able to help more.

Regards

Dave

 

[electricracer]

I too have a problem with the heater. the fans seem to work, both the engine bay one and the front ones. however when you press the defrost button for the screen the fans kick in and run for about 4 secs then switch off. after a further 4 secs they come back on then turn off and this carries on until they are turned off with the switch. the fan that seems to be turning on and off seems to be behind the front bumper( oil cooler? ) the relays in the fuse box are operating turning on and off the fans. my questions are this, is the fault likely to be in the ccu? and is the ccu the box that all the controls are on? and how easy is it to repair the unit and are there any common repairs to be carried out? (dry joints, weak components etc) hopefully you can help

 

[Alexander_Drobik]

If it is turning on/off like that either a sensor/ccu is going, else some form of short is taking place. If all other elctricals are fine then it leads to a sensor fault on the heater control unit. May be the little fan on the back of the ccu although the defrost button pypasses this I beleive. There is a cmpany in italy that checks/recondition those but there have been the odd report of thngs not going to plan (one in the uk too). But I would not start here - I would go to a specialist and let them check what is going on. Too many options to say at a distance change relay xyz.... and yes a failing relay could be the issue may be worth changing whichever ones does the heater circuit(s) would be marked on the fuseboard.

 

[Dave Wilkinson]

Colin,

The symptoms you describe when using the defrost function sound, to me, like a rear blower fan failing to run in fast mode. The fan behind the front bumper (on the left hopefully) will be the aircon condenser fan. If the rear blower is not producing enough air pressure the CCU will cycle the condenser fan as you describe.

If the rear blower runs OK in slow mode there may be a problem with either the relay (also in the rear panel along with the fuse) or the ballast resistor which is snapped into the blower plenum tubing just opposite the rear electrical panel. You can swap the relay with the oil cooler relay - it's identical.

As Alex says, there are places which will repair the CCU but it often turns out NOT to be the CCU at fault.

Regards

Dave

 

[kevin]

I'd check the Rennlist forums for answers to this, I know a variety of answers exist there, for example, remove the relay and jumper it to see if the speed controls work, disconnect the temp sensor in the heater tube, that should fire the blower up even with the ignition off.....

My own issue turned out to be the resister in the heater tube, even though it looked ok, it measured soemthing like an ohm or two, and that was too much, should be about .3 or something silly, spent £10 bought a new one and hey presto no heater faults.......

Try the simple things like jumpering the control relay in the rear box first, CCU problems IME are rare.

Kevin

 

[electricracer]

tried swapping the oil cooler relay for the blower relay and it all seemed to work fine no cycling just lots of hot air[][][]. relay has vw audi part no on so first port of call is a vw dealer then will try opc just to see if any difference in price. does anybody like to place a bet that there might be??????

 

[Guest]

[:'(]I'm going to try the relay swap trick too....once i get some decent weather...wish i had a 19 bedroom house on a 1acre plot...so i could have enough space for a big garage (big enough to work in etc)!

Are the fan heaters any better these days on the modern factory made 996's and 997's?
Thanks again for the tips computamedic chap!
Glyn
C2 964 1991 without aircon

 

[Keith Calder]

my dash fan runs on all 4 speeds when set to cold, when i turn heat up the fan goes down to lowest speed any ideas guys?

 

[Dave Wilkinson]

Fuse blown on rear blower???

Dave

 

[Guest]

there's another fuse box in the ingine bay (right hand side) next to the blower fan from the engine (black round thing). There are fuses to check....also the oil cooler relay swap might help you. My fan went the day after i bought my car......i've tried all the checks...no luck so far....the only one i cant work out how to do (aother check before shelling out a few hundred quid for a new fan even though i'm not sure what the problem is) is to check the resistor that's on the pipe coming from the rear blower fan inside the engine bay. My fans are all lifeless whether the ignition is on and engine off, whether the moon is in equinox with venus....etc etc Annoyance!

 

[Keith Calder]

ill check them tonight while im looking at the sticking clutch problem....new slave cylinder bill coming i think

 

[Keith Calder]

just noticed i have same problem as electricracer, when i switch on screen demist function the aircon fan runs for 5 secs then off for 2 secs then on for 5 secs. so fingers crossed removed oil cooler relay, opened engine lid, tried to unscrew fusebox cover, too tight, tried screwdriver, too tight, 10mm spanner cracked it swoped relay and yes its sorted, thanks for help! the relay does have a vw part number but remember going to vw dealer for a relay for my 924 turbo and it was dearer than a porsche one ..strange...

 

[Keith Calder]

right....now i have a fully working heater i have realised the air con is still switching on and off, ive checked around and finally ended up at the resistor box under the front wing..... i just touched it and it fell apart in my hands...rang porsche and quoted part number 964 616 521 01 for replacement but they say its been replaced with 993 item about £30 so nearly sorted? the problem i have is removing the old one, does anyone knows if it screws out or prise out, i dont want to cause any more damage! thanks

 

[Keith Calder]

just found out its held with a 4mm allen key...great! just where you cant reach it! may have to drop it out to swop it...