Climate Control goes cold at higher speeds

[Blue_Thunder]

This is a bit of a weird one which has been bothering me for a while.

I've got the pre-facelift climate control in my 98 S4 which used to work a treat. I've noticed that over the past few months, it seems to be going a little crazy.

When cruising at motorway speeds, you have to turn the temperature up by about 2+ degrees, otherwise it gets quite cold. I thought I was dreaming at first, but on a long journey with occasional traffic jams, it was noticeably warmer when we were going slower or at a standstill. I'm sure it never used to be like this. I suspect one of the cabin temp sensors might be knackered(think I remember reading that there are 2), but don't know how to measure what they are reading. Can't find it on Vagcom anywhere.

Anyone else had this?

 

[aragorn]

could it not just be heatsoaking the aircon rad at lower/stationary speeds and therefore being unable to maintain the temperature youve set?

 

[treblesykes]

check the compressor drive belt and/or aircon gas pressure. It seems to me its not that the aircon gets colder while you are reving the engine, more that its not working so well at low revs

 

[Blue_Thunder]

Good points, but I don't have aircon anymore since my last engine pull. Someone must have cracked a pipe or something and i've been quoted £400 to get it sorted

If I set the temp at say 20 degrees, allow the cabin to get to a comfortable temp, then drive at 70, the cabin will get noticeably colder. In order to keep it so it feels the same temperature, you need to put it up to 22-23.

Think the problem is more that the climate control unit doesn't know what the cabin temp is, as even if the air coming through into the unit changes temperature, the climate control unit should just mix more warm air with it. I think...

 

[aragorn]

sounds possible, but ive no idea on how it works as my car doesnt have that shineyness!

Sounds pricey to get the aircon fixed, perhaps if you got the pipe yourself from a breaker or similar you'd only have to fit it then pay for a regas?

 

[Blue_Thunder]

sounds possible, but ive no idea on how it works as my car doesnt have that shineyness!

Sounds pricey to get the aircon fixed, perhaps if you got the pipe yourself from a breaker or similar you'd only have to fit it then pay for a regas?

It was a few months ago now, but i'm sure my garage told me it would need a new aircon compressor because one of the solid lines off that had cracked. Could probably pick one up for <£100 off eGay, but it's the fitting which costs megabucks because it's supposed to be a real PITA to get the compressor out in the S4.

You can barely even change a bulb in the S4 without doing an engine pull! lol

 

[AndyMac]

You haven't got aircon, but you expect the climate control to behave itself?
Sorry I'm completely confused. CC is just the control unit for the aircon, without the AC working it can't possibly work properly.

 

[Blue_Thunder]

I don't understand how having my aircon working would prevent my cabin temperature from dropping when at cruising speed...

 

[AndyMac]

It's not your cabin temp dropping at higher speeds, it's your temp rising when in traffic.
With no working aircon it has no way to cool down the cabin. Stuck in traffic you have hotter air everywhere. Isn't this really obvious or am I missing something?

 

[aragorn]

Yer thats what it sounds like to me, without working aircon it cant actually have any way of adjusting the airtemp other than blowing in whatevers outside, and when its warm thats probably not any use.

I find it hard to believe that the aircon compressor would have non removable pipes on it that could be damaged. Vagcat seems to agree with this: http://www.vagcat.com/epc/cat/au/A4Q/1998/219/50/2646710/

So i'd imagine you should be able to get the pipes from a breaker (or audi if they're not too dear) and hopefully be able to fit them without dismantling too much of the car!

 

[Blue_Thunder]

I can be driving at 50 and it's still warmer than at higher speeds. If the aircon is not on and the cabin temperature is lower than the ambient air temp, you'd expect the climate control to at least reduce the fan speed to minimal, which it doesn't really do.

I'm convinced one of the temp sensors is shot, just don't know a) Where they are and b) How can I measure what they are reading at any given time?

 

[AndyMac]

I'd concentrate on sorting the aircon mate, forget the temp sensors until you have a working system. CC is never meant to be switched off so god only knows what strangeness will be going on with no working aircon.

 

[Blue_Thunder]

Noticed this morning when driving to work that the outside temp was reading as 18 (so assume the inside temp was no higher than that as the car is parked in the shade). Had the climate control set to 21 but it was blasting out cold air - engine was up to running temperature.

Turned the CC up to 22 and it started to come through warm. Defo think it's an interior temp sensor.

There's not a chance i'm getting the aircon sorted. Think I might even get rid of the heavy lump if I go with an FMIC later on this year.

 

[aragorn]

http://www.vagcat.com/epc/cat/au/A4Q/1998/219/56/2652658/

that seems to show it mounted in the centre console and the sun sensor in the top of the dashboard.

 

[aragorn]

http://www.vagcat.com/epc/cat/au/A4Q/1997/157/56/1774288/

that image is slightly different for earlier cars (97 instead of 98) but i cant really tell where it is?