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Old 08-16-2005, 01:57 AM
skiier3_9's Avatar
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Join Date: Jan 2005
Location: Minnesota
Posts: 975
w220 '00 S500 A/C question about recharging

my father claimed that his 00 S500 wasn't blowing cold enough and/or wasn't cooling fast enough so I hooked up the R134 gauges and temped the vent temp:

with engine idle (68F ambient) and both climate controls set to LOW/high blower fan

30/130 PSI (low/high side pressures) vent temp 52F

The pressures seemed to be a bit low so we attemped to add some R134 however, with the low side open (not the air, just to the can) and the high side closed the system did not want to take any more refidgerant even after 5-10 minutes of idling...during this time there was no change in vent temp either. I would have expected this car to blow <40F vent temp (especially with ambient only around 70F).

BTW: No rear A/C (or CC unit) in this particular car.

Any ideas??

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Old 08-16-2005, 01:13 PM
MrCjames's Avatar
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Join Date: Jun 2003
Location: SF Bay Area
Posts: 599
FYI: the compressor on your vehicle is a direct drive system, no electrically controlled clutch (always on). The AC system on this vehicle operates by using a PWM (duty cycle controlled) signal to a control valve which alters the crankcase pressure inside the AC compressor. The altering of this pressure allows the variable displacement compressor to deliver refrigerant from a minimum of 10% (short cylinder stroke) to a maximum of 100% (long cylinder stroke). When crankcase pressure decreases (low pressure on one side of the pistons) the compressor increases the output volume (Large pressure differential between Hi/Low). When the crankcase pressure is increased (near equal pressure on both sides of the pistons) the volume is decreased (Small pressure differential between Hi/low).

Sort of like taking your hands and making two fists, place them knuckle to knuckle and begin pushing. If both hands push with equal force your hands hardly move, reduce the force applied by one hand and the other hand begins to move away from the starting point.

Enough about science already how do we fix your car! If you insist on trying to solve the problem your self try revving the engine up to about 2200 to 2500 and see if you can get the AC to accept more refrigerant. I would strongly encourage you to find a facility in your area that has the AC equipment so it can be serviced with the exact amount required for optimal performance.


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