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Old 10-26-2001, 09:39 AM
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Question AC Sight glass color after Evaporator Replacement

I just had a 3 K evaporator job done to my 1994 S-500. The Receiver/Drier shows very few bubbles at startup but it also shows slightly cream colored with a slight green tint from the leak detection dye. The AC shop removed the freon, weighed the charge, which was exactly the right amount and evacuated the system again. After recharge the glass remained cloudy. They say nothing is wrong and in R-134 systems the sight glass should be ignored. They did say when they over filled the system by .3 lb. the glass cleared up but the pressures went too high. Do I have anything to worry about?? During the evaporator replacement, the expansion valve and the Receiver/Drier were also replaced.

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Old 10-27-2001, 02:07 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
I charge them by weight and the glass. I use the BMW method...I look at the glass, when it appears to cycle, cloudy and then clear, that's it.
Donnie Drummonds
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Old 10-29-2001, 09:21 AM
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Join Date: Jun 2000
Location: Plano, TX
Posts: 2,476
I've always heard the sight glass is not useful for 134a systems. Newer cars have had the sight glass removed from the receiver/dryer - my 210 doesn't have one.

Charging until the sight glass is clear on a 134a system almost always means the system is overcharged, and overcharging is one of the worst things for an a/c system.

One explanation for the cloudiness/bubbles in the sight glass is the (usually) PAG oil inside the a/c system is less miscible in 134a than the old mineral oil/R12 systems. Hence what you are seeing is an emulsion of liguid refrigerant and oil droplets moving through the system. Adding more 134a increases the high side pressure and temperature until the PAG oil finally mixes completely - that's when the sight glass clears.
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