05-24-2009, 09:22 AM
Location: On The Move
Join Date: Jul 2003
Mein Auto: 09 Freightliner
Small A/C Service
Date: 5/22/09, mileage 66,393.
Observation: Car has a distinct lack of "coolness" in A/C effectiveness lately. Also, there seem to be what I would call high-pressure cavitation or "hiss" sounds that are very noticeable near the vents.
Diagnosis: Low on refrigerant: Conduct refill procedure.
Environment/settings: Ambient outside temperature: 80F, 80%RH (est).
Car settings: Temp: 59F, Mode: Auto, Mix: Full cold (3 blue dots), Int/Ext: Full Recirc. Air outlets: Open. Engine running, doors and windows closed.
Supplies: Refrigerant: R-134a w/ "Sub-zero synthetic A/C Booster." Weight before: 1 lb, ½ oz. Weight after: 3 ½ oz. Consumed: 13 oz.
EF Products refill gauge / hose combo. Uncalibrated.
Pyrex Professional digital cooking thermometer with probe. (*)
1) Take current temperature readings at left, middle and right outlet ducts: 44F, 53F, 50F.
Note: Allow thermometer probe to settle 60s between readings.
2) Note system LP side pressure reading before fill: 28 psig
3) Attach refrigerant can, open fill valve, allow to fill for 15 minutes.
4) Repeat temperature readings. After fill: 41F, 39F, 39F.
5) Note system LP side pressure reading: 29 psig
6) Result: Cavitation/hiss noises are now absent, car is nicely cool.
Reference thread (previous DIY): http://www.bimmerfest.com/forums/sho...92&postcount=6
Clearly I have a slow leak somewhere, as this is the third can of refrigerant added to the car (Jan 08, Mar 08) since purchase. Will continue to monitor.
As a final note, there is a BMW AG Sticker under hood: "WARNING: R-134a only. System Capacity 1.63 lb (26.08 oz) plus or minus 0.05 lb / 740 g plus or minus 25g." As a result, I calculate I filled the system by 13 out of 26.08 oz, or approx 50% of capacity of refrigerant of the car. Since the car was cooling, albeit poorly, prior to the fill, I reckon it has somewhere on the order of 75% of the fill now.
Last edited by MMME30W; 05-28-2010 at 02:39 PM.