2007 W221 S500 climate control cooling issue

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Grob

New Member
Joined
Apr 5, 2013
Messages
21
Location
Dublin
Car
2007 W221 S500
Hi.
I am stuck on what could be wrong with the climate control on my car. It have very poor cooling and once it get over 20c outside its next to nothing. It have a new Denso compressor, condenser, expansion valve, dryer and pressure sensor, evaporator temp sensor and has been flushed a couple of times. It passes all the guided tests on mb star and shows no fault codes in the ACC or SAM or anywhere else. The coding shows the correct options and the correct compressor is selected. Pressure show say 12bar on the high side and maybe 3- 3.5bar on the low side but no lower on the low side. It has the refrigerant drained and flushed maybe 3 times with no change in preformance. The evaporator temperature will drop to maybe 5c on the lowest fan setting but as soon as you increase the fan setting it will rise up close to ambient. I have been to a number of so called specialists but no solution yet. Alternator shows no faults and produces 14-14.4v.
Anyone have any ideas??
 
Wow, you have been through the ringer solving this one!

My thoughts/guesses as a DIY'er recently diagnosing my own aircon issues:
- Failure in the heating side of the circuit, meaning the heater matrix is always getting hot regardless of cooling request. Does the aircon work any better immediately after a cold start, i.e. before any heat in the coolant?
- Faulty cabin temperature sensor, meaning the car believes cabin temp is already lower than demanded (would expect the variable displacement compressor to be commanded to off/5% in this scenario though, and you say you are seeing good high/low side pressure differential.)
- Faulty air outlet temperature sensors, according to WIS, a 2007 S500 has sensors in the air vents that send outlet air temp data back to the climate system (does the aircon work any better if you force air distribution to screen, footwell etc. rather than leave it on Auto?)
- Blocked/failing evaporator, do you have any odd smells from a possible cabin side refrigerant leak? (though I would expect to see overpressure fault codes with a blocked evap).

Overall though, from what you say, it sounds like the core mechanical components of the system are all working. This 'feels' to me like an electronic/sensor issue, rather than a core mechanical issue. If it were me, I would be looking closely at the commanded duty cycle live data for the compressor - if the actual cabin temp is higher than demanded cabin temp, then you should see the compressor duty cycle increase in the 50%-100% range. If that is not happening, then it is because the relevant climate ECU does not feel that cooling is needed, thus there is a sensor feeding different info compared to expected.

Martin.
 
Hi Martin.
Yes it has been a pain. The evaporator temperature has been replaced. All the other sensors read ok and are close to each other. Cabin temperature sensor seems to reading ok and reads ok when you warm it up. Makes no difference on what position the airflow up or down. I can only see through my c4 that the compressor is consuming 750 mA but I can not see / find the duty cycle. I am thinking climate control ecu or maybe the SAM but no fault codes so hard to know.
 

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