SOLVED: RS4 B7 Air Con AC only working on LO Max Cold setting

[JamesBaby]

My RS4 B7 had an issue where the AC worked fine on full cold 'LO'' setting, but whenever you selected a specific temperature the climate control would just blow luke warm air at a steady rate. It wouldn't adjust or modulate the air to maintain a specific temperature. So eventually you started to get too warm in the car. There were no fault codes stored, and all the flaps and motors worked as they should directing the air flow to the required areas.

I thought it was the AC itself at fault so obviously had it re-gassed etc, but it remained the same. I then changed the orifice filter in the AC pipes and had it properly vacuumed and re-gassed. Still no difference. I used VCDS to re-set the various flaps and motors several times to no avail.

I measured the performance of the AC using VCDS when on LO setting and an AC expert said the results were normal. It then dawned on me that this fault still exhibited regardless of whether the AC was on, or in bypass mode by pressing the ECON button. So it couldn't be AC system related. This then led me to believe it was a sensor or even climate control unit issue.

I cleaned the cabin temperature sensor which is the 3 little grill slots at the top of the climate control unit with electrical contact cleaner (power off).
I set about replacing the temperature sensors in stages as they would be the cheapest to do, even though they had no fault codes.
I replaced the air temperature sensor in the 'fresh air intake' under the pollen filter. No effect.
I replaced the air temperature sensor in the passenger side footwell, in the centre console. No effect.
I replaced the 2 air temperature sensors in the centre console directly behind the Climate Control unit, under the head unit. No effect.

I then swapped out the Climate Control unit itself with a used one from an online breaker. RESULT !!. It works and is now modulating the cabin temperature to the desired setting. So to fix this issue, unless you have a fault code to resolve, you need a replacement climate control unit. I found a used one online for £70. The front facia had more wear than mine so I unscrewed it and swapped it over.

I thought I'd post this up here as there were hours of google searching on various forums but non resolved this issue. I only found issues of flaps, or AC pressure switch, or warm air from the left side only etc etc.

[delroyx]

Thanks for sharing this. Good to keep the forum alive especially with solutions to problems these cars are increasingly likely to suffer with given their age