Hi all - 1992 RHD 968 with the following heater issues

- intermittent heat. With heater on I sometimes get heat, but generally not. When I am trying to get heat AND am getting heat, then when the heat stops and it starts to blow cold air, then the fan speed can also be heard speeding up (or possibly some other flap opening that makes it sound noisier?) (i have no reason to believe I have any air entrapped in the cooling system)

- when I move one of the heater slides, then yes I can divert air flow to or away from my feet. That works fine.

- when I move the other heater slide it does not result in any mechanism movement at all (i have checked that the rid with the clip that often comes loose is all intact. I have removed the rod linkage from the splined servo motor and all flaps move fine. It seems that the servo motor is not working )jammed? No signal to actuate when control lever moved?)

- I’ve made an initial check of under hood vacuum lines and Y connector and all seems properly connected and in pristine condition.

- I’m aware of the heater control valve at the rear of the engine (my 928 S4 has the same system) and that it defaults to hot. The fact that I sometimes cannot get any heat suggests I am not suffering the default to hot problem.

so where to start? I am on holiday in New Zealand with this car, taking it back to Australia in April. So I am well away from all of my tools and multimeter and vacuum testers etc. and we will be heading to the South Island soon where in spring it can get pretty cold. And demisting may be important.

I think I’d like to check the non operating servo motor to make sure that actually works. There are 5-6 pins on the electrics yo that motor. Which one do I put power to and which one do I ground just to do a simple electrical check on this motor?

any other simple suggestions (complicated can wait until I get it back to Australia.

thanks in advance - apologies for the lengthy post.

regards

dave

 

Sounds exactly like the issue I was getting with a leaking vacuum accumulator, the one on the firewall by the battery. I would also make sure your vacuum check valves are working correctly, iirc there is one by the brake booster that checks the vacuum accumulator.

Edit: Ok Australia, so if your car is RHD then the accumulator is not by the battery, my bad, it’s by where the battery is on LHD cars.

 

Hi Magk944, thanks for your response. I've checked the vacuum accumulator (sucked on the 'elbow') and it seems to be holding vacuum. I think further investigation may have to wait 'till I get back home...

Cheers

DaveO