Originally Posted by
saintsdesignandprint
Hi im sorry I know this is an old thread, I have an 04 also ... ive followed as above, clamped off the one hose coming out of the duo and also cleaned the duo and lubed, ... made no difference.
I had the car re gassed a week ago and it was fine for 3 days then went warm,
I went back to the garage and they checked and it hadnnt lost any gas, they did another gas regen anyway ... this time it didnt go cold at all...
The clutch is engaging on the compressor when i press the ac button, you can hear the fan noise change also when the ac button is pressed. The metal pipe that runs behind the headlight is ice cold ...
The garage said the think its a stuck mixer flap behind the dash but they have no experience with MB or crossfires ...
any help or advice much appreciated ...
Is the A/C dropping out cause the ECU senses overtemp of the engine? Or maybe the charge in the A/C system is too low or high- that will also cause the system to disable the clutch - are you SURE that shop knows what its' doing?
(Let me answer that - they don't.)
THe big question is this: Is the A/C clutch disengaging or is the clutch staying engaged? Because the answer to that tells us where the problem is. Cant ANY shop diagnose a failure anymore? I know here in America, we no longer teach analytical or critical thinking - is the UK this vapid as well?
Theory one: Clutch does not stay engaged
The clutch is controlled by the ECU, not the Climate Control Module (CCM), the CCM asks the ECU to operate the clutch, but the ECU can cut out the clutch if you accelerate and need the power, or if the engine seems to be getting too hot. The ECU has control. Does it see something it is trying to manage?
Theory two: Clutch stays engaged
If the system does not cool with the clutch engaged, then the charge is not right, probably too low OR the expansion valve is bad OR the system cant' get rid of it's heat, therefore it can't make "cold" - so, is there a lot of air flowing over the condenser? Does it cool better at 80mph than sitting still?
It's usually the duovalve passing coolant when ti's not supposed to, but it can be an actual A/C system failure - but it can also be that the ECU is trying to 'save' the engine by turning the A/C off due to some issue it thinks exists. Now, most shops you PAY to work on the system don't know what I just told you - because they hire unqualified, untrained people. Dealers are worst about this.