climate control problem

[JOB]

Hi Everyone!

This is my first post and I must apologise because it is very long but I wanted to as detailed as possible.  

I have a 2001 Audi A4 1.9TDI. It has been in the family since new and has covered almost 380,000kms (It started life in Germany).  I have replaced the timing belt, DMF and replaced a number of suspension components.  It still drives great and is very much loved by the family.  

Recently the the air con stopped blowing coid air. All  other functions on the Climate control are working normally.   

I took the car to kwickfit and they regassed the system and it was great for two weeks and then it started to blow warm air. I suspected a leak so I had the system presure checkecd and the presure had not dropped.  

I checked the power supply to the AC compressor clutch and there was no power when the climate control was turned on. Using a power probe I am able to energise the clutch when I supply a feed. I traced the circuit back to relay 267 which powers the clutch and everything checked out with the exception of the supply that triggers the relay. If I bridge the relay I the AC clutch kicks in and I get cold air. 

When I was checking the connections to the AC clutch, condenser fans and High pressure switch the AC started working. I thought it could be the High pressure switch because it is common. I replaced this and I still have no trigger supply to rely 267. 

I managed to find a wiring diagram for the climatic control and if I am reading it correctly the trigger wire comes from the A/C Control Head E87. More research found a very very cool diagnostic feature of Climate control where you can collect all of the measurement values and check for errors C1. I went through of the values and noted them down. The first value C1 does not indicate any stored faults. 

I also noticed that the outside temperature is no longer displayed in the instrument cluster. I have a problem  with my fuel and temp gauge. Taking into account it is a German car I have not come across a second hand instrument cluster. The temp gauge and fuel gauge problems existed before and the AC worked without any issues. 

When I looked at all 60 values I noticed one value that looked strange. 

C41: outside (ambient) temperature, unfiltered, (internal software, in deg c) has the value 0 I wonder if  the AC control thinks the temperature is 0 it will not trigger the relay to energise the Air con compressor clutch. I checked all of the temperature channels and they are all reading correctly which makes me think it is not the ambient temperature sensor and it is the A/C control head. 

These are the  values and channel numbers.

55: Outside (ambient) temperature, in deg C or deg F depending on setting on A/C control head =  25C
56: Temperature in deg C, from Interior Temperature Sensor, in Headliner (G 86) = 23C
57: Temperature in deg C, from Interior Temperature Sensor, in Instrument Panel (G 56) = 34C
58: Temperature in deg C, from Fresh Air Intake Duct Temperature Sensor (G 89) = 41C
59: Temperature in deg C, from Outside Air (Ambient) Temperature Sensor (G 17), front = 26C
60: Temperature in deg C, from Ambient Temperature Sensor At Fresh Air Blower (G 109) = 44C

The Air Con conpressor off code is.

52:  A/C compressor switch-off conditions = 14 Some data charts list 14 as a data bus fault.

I ran through the channels again but this time I unplugged the outside ambient temperature, behind the bumper. 

55: Outside (ambient) temperature, in deg C or deg F depending on setting on A/C control head =  27C
56: Temperature in deg C, from Interior Temperature Sensor, in Headliner (G 86) = 26C
57: Temperature in deg C, from Interior Temperature Sensor, in Instrument Panel (G 56) = 34C
58: Temperature in deg C, from Fresh Air Intake Duct Temperature Sensor (G 89) = 38C
59: Temperature in deg C, from Outside Air (Ambient) Temperature Sensor (G 17), front = -48C  (sensor unplugged)
60: Temperature in deg C, from Ambient Temperature Sensor At Fresh Air Blower (G 109) = 44C

C41: outside (ambient) temperature, unfiltered, (internal software, in deg c) has the value 0 the (sensor unplugged) 

I was wondering if anyone has experienced a problem like this or if anyone knew if C41 should be 0? I don't mind driving with the window down but my better half has said maybe it is time for a new car. 

Many Thanks!