Blower sometimes

dependencies · 10-17-2007, 11:28 AM

What causes this please....

turn motor on

turn blower on momentarily fan noisily blows
then it stops.

turn down the temp knob

blower comes on again (usually)

or instead......

engine on,

push demistor button
fan blows again for about Two seconds, stops?

fuses all intact BTW I checked them first

dependencies · 10-18-2007, 11:54 AM

Strange I'm apparently the single person to have experienced this phenomenon,
has anybody then had ANY problems with their blower/fan

I'm thinking possibly a problem with rear blower in engine bay
given mine will supply cold air properly, but not warm

anybody got any suggestions...

Manipou · 10-29-2007, 01:38 AM

I have just logged on to find if anyone had this exact problem.

My 964 does the exact same thing. Has no one had this problem before?

Thanks

dependencies · 10-29-2007, 05:30 AM

If they have, they are keeping quiet about it,
Quite like to see a few solutions before I hand over frankly a lot of earnings to plug in a new control unit, and find its not that.

Perhaps you can offer some more specific symptoms, see if that prompts a response

Cheers Richard

UK

bazar01 · bazar01's Garage

Mine has about 95k miles on the clock.
I've never had problems with my heating nor my a/c system yet.

It's probably the best time to get familiar with the system while it is still operating properly.
I am planning on seeing how the three fans and servos work together with my own eyes sometime this month.
There are lots of write-ups on the net but there's nothing better than seeing it personally with your own eyes.
I'll keep you posted on what I find out.

dependencies · 10-30-2007, 04:26 AM

That might be interesting although TBH the amount of related servos and such inside the panel behind fuel tank,

Looks quite daunting, having said that, I'd like a run down of what happens when I turn up. The thermostat alone...

Good luck, I look forward to reading and hopefully seeing pics

Richard

bazar01 · bazar01's Garage

Played with my cabin heating system today.

To see whether the heater blower is ON, I hooked up a magnehelic gauge on the discharge duct. (at one of rubber hoses for dizzy vent kit)

At 85F cabin temp, and temp knob halfway (75F), heater blower in engine compartment is OFF. This is because the temp set point is satisfied. Vent supply air temp is at ambient.
Heater blower only comes ON at temp knob setting when CCU is calling for heat (that is when cabin temp is less than temp knob set point).

Once temp is satisfied, it turns OFF but the cabin blowers are still ON until they are turned OFF at the blower switch knob..

Next I'll play with the servos and mixing valves when I get the chance.
Weather is just too nice to fool with the car..

dependencies · 11-16-2007, 12:07 PM

Bazar01
YHM

unclebilly · unclebilly's Garage

Hook it up to a Durametric or similar. They can read your HVAC computer. Durametric showed that I had a flap sticking and I was having the same problem.

plain fan · 11-18-2007, 07:09 AM

When you ask for heat is the temperature in your car noticably cooler than the desired amount of heat? It could be that it kicks on just long enough to measure the difference in temperature then turns the fan off.

dependencies · 11-18-2007, 07:21 AM

Quote:

Originally Posted by plain fan

When you ask for heat is the temperature in your car noticably cooler than the desired amount of heat? It could be that it kicks on just long enough to measure the difference in temperature then turns the fan off.

While I see what your getting at, certainly in terms of 'getting car out of garage' in the mornings
initially it seemed to produce flow of hot air on demand in much the same way any water cooled car would.

But later in year and colder I suppose, the fan would go on and then almost instantly of again, which suggests its a fault somewhere, and not that cabin has in anyway achieved comfortable temperature or is likely to without car in motion and forcing air through from engine.

cjoenck · 11-18-2007, 07:48 AM

I had some very similar issues. First of all, do you have access to a diagnostic scanner like the Bosch Hammer or the software from Durametric? The fault is most likely in the CCU and this critical component has its own set of error codes. One possibility is that the temperature sensor in the CCU is broken. You can get a replacement part - the actual CCU is $1,600 new - for around $100. The part number is 964 618 943 00. If you have access to another 964, pull the CCU and see if a different solves the problem. The exchange is extremely easy, it pulls out like a radio.
If the CCU checks out, make sure your resistor in the air duct coming from the main engine compartment blower in the back is working correctly. Another cheap part that is easy to replace but causing all kinds of problems when broken.
Finally, check you blower sensor as well - part number 964 659 148 00

Hope this helps.