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Poor AC performance / clutch always engaged in AUTO

1469 Views 5 Replies 3 Participants Last post by  _viktor_f_
So before leaving it to the shop to get the AC recharged, I just wanted to vent my thoughts with you guys.

Car is a 2003 wagon VR5 (european) with Climatronic. When in AUTO mode, the compressor clutch is always engaged (does not cycle on/off). When in ECON mode the clutch releases (as expected) so that's fine.

Bought the car second handed with the 00792 - A/C Pressure Switch (F129) fault code - found a blown fuse for the condensor fan (below the dash) and in the end I found out that the fan was shot so I replaced it. This fault code has not re-appeared since so it was probably a high-pressure situation due to the non-working condensor fan (From what I have read, the F129 covers both high and low pressure faults).

I have fault codes also for the V68 temperature flap, the V70 central flap and the V71 air flow flap. I'm not so concerned about the V70 and V71 in this matter. These motors move verified by sound and VCDS (lite). The V71 is out of specs in terms of position (255 for fresh airflow and 60-something (oscillating) for recirculation, compared to 231 and 31 which are the defined values respectively but it actually moves between these values) I could see a problem related to the poor AC-performance (naturally) with the V68 temp flap error code. However, when I monitor the position of that flap with VCDS lite, the measured value always matches the specified value also when changing set temp on the climatronic.

Anyway, going to temperatures (translated to Farenheit): Outside temp 62F and before starting the engine: Center vent (G191): 70F and Evaporator temperature (G236): 75F
Engine on, temp setting "low", air to face, blower fan at lowest: Center vent (G191): 48F and Evaporator temperature (G236): 57F
Engine on, temp setting "low", air to face, blower fan at highest: Center vent (G191): 59F and Evaporator temperature (G236): 66F

So yes, it is chilling the air but it feels a bit weak and the temp inside the coupe is not really comfortable still, even with ambient temp of 62F and sunshine. I'm a bit confused with the evaporator temperature beeing higher than the center vent temp... I felt the temperature on the refrigerant lines at the firewall, one was REALLY cold and the other one approx room temp.

Anyway, my analysis is that the system is low on refrigerant (but not too low so that the F129 kicks in) and even though the compressor clutch is always engaged, the temp in the evaporator is still not low enough. Also an indication is the experiment when going from low to high blower fan - the evaporator temp is increased (here, I would expect the duty cycle of the compressor clutch to be increased to cope with the increased heat load on the evaporator). But the duty cycle is already at 100%....

So the bottom line: Take it to a shop to get a proper evacuation and recharge?
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The temperature control flap directs the air through the heater and/or the AC, if it is stuck half way you will get about half hot air and half cold air.(= warm air)
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