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Old 05-24-2009, 09:22 AM
llando88 llando88 is offline
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Join Date: Jul 2003
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Mein Auto: Ram 2500 4x4
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, ˝ oz. Weight after: 3 ˝ 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):

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.
“Character is doing the right thing when nobody’s looking. There are too many people who think that the only thing that’s right is to get by, and the only thing that’s wrong is to get caught.”

- J.C. Watts Jr.

Last edited by llando88; 05-28-2010 at 02:39 PM.
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