OK gentleman I picked up a new 928 today to replace the 88 S4 I've had for 3 years. New one is a beautiful 92 (must be one of final ones, or at least last ones to sell!) Amazon Green S4 with only 65K miles.

Need to change my avatar and sig!

I was expecting to find a few issues on first day with the car (see my post re kickdown switch) but she drives and feels fantastic.

There's an odd HVAC issue. I haven't checked vac actuators yet (though flappy works which is good sign) but it is blowing very warm air at coldest setting. May be temp sensor or may be the hot water valve but will investigate.

The aircon blows very cold for first few minutes after it's turned on, but then gets warm. I know little about aircon systems so is this likely to be a sign of being low on gas or something else? Had a look at top of drier on drive back but the glass was not clean enough to let me see if any bubbles.

Thanks in advance.

 

Maybe the freeze switch is not working or is bypassed. Do you notice a reduction in airflow when the air gets warm? It could also be a tired relay in the A/C control box.

Dan
'91 928GT S/C 475hp/460lb.ft

 

I would check the heater valve. Maybe tired and stuck, making the air warm no matter what setting.
I think you can "manually" close it with a zip tie to test. Could also be vacuum related with the heater valve.

Search for posts by "Dwayne" he recently did a fantastic write up with pics about HVAC and Vacuum.

 

Thanks guys. Yes I had read Dwayne's excellent write-up and will draw on it as I sort HVAC out.

I changed the heater valve in my old 928 and checked out each vac line so this should be familiar.

Was just puzzled that air would start blowing cold, but then get soupy.

Anjyway will start with the heater valve and the system behaviour without aircon on points to possible problem there (hope it's not internal temp sensor as remvoing centre console tedious, and really hope it's not a problem with main controller).

 

Controllers can be repaired quite easiy.

 

Thanks for reassurance John. The car is wonderful, but I'd overlooked some things on my inspection which I should have known about as 928 owner. Door stays are also on the list!

 

You may not really need door stays. IF you remove them, and clean off all the accumulated & hardened grease, then put a thin layer of a Teflon containing grease (I use Superlube) on them, re-install, and they will work great (at least 6 have for me). I find "really new" ones are extemely stiff, but those I refurbished by this technique are appropriately firm, and hold the door open nicely.
Best wishes on a great car (assume GTS).
Cheers,

Gary Knox
West Chester, PA
USA

 

Well if it initailly blows cold - I'd say the AC is fine - low on refrigerant would usually not get cold quickly.

Sounds like as soon as the coolant wams up you have a problem - that most likely suggests a sensor loop problem so I'd start there. check for the existance of the ext temp sensor.. look under the LHS (pass for you) Headlamp - you will need to remove pod cover and headlamp and lower the lights to see it....

If it's there check connectivity & function (see previous posts on this..)

Alan

 

That's very useful Alan, thanks.

I'll take a look at the ext sensor. In past I've also checked it (last 928) by removing wheel liner which gives very good access.

The aircon will blow cold again if I turn it off while still driving, then turn on again some time later (not done any rigorous timing on this), so I get the behaviour even when the car is fully warmed up.

Will look at the hot water control valve first. If that checks out ok then will move on to the sensor(s).

 

You can get better access with the wheel liner & splash shield off - but its far quicker to remove the headlight - and access is OK to check this. If the alternator hose is missing you will need to take the liner & splash shield out anyway - but the headlight access only takes 5 mins...

While the water valve may have failed - unless the temp loop or setting motor is broken - you would not get full hot... the water valve is often supposd to be open (leading to a heater core full of hot water) during AC mode - but you only feel it if the mixing flaps are open...

All temperature regulation is via partial air circulation though the heater core - even in AC mode - so as soon as you have cooled the car to the set temperature you will open the water valve & start slight warm air mixing to maintain the set temperature... In AC mode the compressor funs full bore all the time (until it freezes the evaporator)

So in summary - it can't only be a problem with the water valve - in fact I wouldn't even start there diagnostically (its obviously open) ... However if you need cool air tying the heater valve shut will probably work - however your AC may then freeze you...

(but you can always turn it off)

Alan

 

I guess I don't see how the scenarios I noted would ever get better with the AC off -> back on after the car has warmed up...

If it really does that maybe it is something else...

Alan

 

OK Alan. It's puzzling but will report back when I have checked out the sensor and maybe water valve for luck. Will go in via headlight aperture as you suggest.

 

That's intriguing Gary. Do you still have to remove door panels to take them out?

Thanks for best wishes - it's actually a very late S4.

Adrian

 

I had this behaviour after I changed my heater valve when I first got the car. Was very noticeable on a long drive inland on a hot day - it was swinging from cold to warm intermittently. I could wiggle the temperature slider off full cold and back again and it'd get cold for a bit, only to go warm again.

When I pulled the side off the centre console and checked all the actuators at the manifold, I discovered I had a slow leaky comb flap actuator.

Since replaced that, and now have working climate control.

You probably have a small leak somewhere in the system that's losing pressure. Putting the temp. slider to full-cold usually pumps vacuum to close the recirculation flap, which explains why a wiggle would cause it to go cold again, as the heater valve gets closed anew. Same with turning it off/on again I think?

 

Thanks Hilton - very helpful if you had similar symptoms/fix. Will check all the actuators for leaks