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Questions and Answers

Charging An A/C By Sight Glass

Q. Question: How do you read an A/C sight glass? First I saw large bubbles. Charged a bit, now foamy white, almost solid. Am I trying to make it appear absolutely clear?

1992 Ford Taurus Wagon
3.0 liter
Automatic transmission
127,000 miles


A. Using the A/C sight glass is only a general indication of how much refrigerant is in the system. The best way to charge an A/C system is with approved A/C equipment.

In general, a clear sight glass indicates a system that is either completely full, or completely empty. It will be readily apparent which it is by the A/C operation.

The white cloudy appearance you are seeing indicates the system is low on refrigerant. Using the proper equipment, you can add refrigerant to the low side of the system until the sight glass just turns clear and no more. You will over charge the system if you go past that point.

In fact when I used the sight glass to charge a system, I leave a bubble or two to allow for refrigerant expansion. I must say, if you are unsure on how to do this or which is the low and high pressure ports, don't do anything. Take it to a professional and let them do it. You can do great injury to yourself if something is done wrong.

Additional Information provided courtesy of ALLDATA

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