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Old 07-02-2011, 11:23 PM
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Location: central Texas
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Roy, in a backward way he did...of the only two cars in the list in his signature that are not sold or crunched... only one is a Mercedes.. so I assumed that was the one in question...
But everyone should say in the first sentence which car they are talking about...

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Old 07-02-2011, 11:30 PM
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Location: central Texas
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Originally Posted by tyl604 View Post
Leathermang - I follow your posts and agree with you. However is it not correct that you can postulate low Freon if there are bubbles in the sight glass. At least that's what I remember from the good old days. My 81 300SD looks like a river current of bubbles going through the sight glass - and all the shops around here want to put Freeze 12 in it (not going to happen).
You did not put a question mark but I will assume one and answer the question..

NO. it is not correct that if there are bubbles in the sight glass one can be assured that the freon is low. You can ' postulate' if you want to ... but 'postulation' should not be acted upon concerning the amount of refrigerant.... LOL

That is stated specifically in the FSM ... as a warning..
and one of the conditions which can cause that false ' low' is a lack of sufficient air across the condensor during the test or filling... one of the reasons I preach sticking a blower putting air into the front of the car when charging or testing ....

Another way of saying it... bubbles can be caused by things other than being low on refrigerant...
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Old 07-02-2011, 11:53 PM
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Leathermang - that's interesting. So what's the purpose of the sight glass?
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Old 07-03-2011, 12:06 AM
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You can tell if the system is totally empty, you might can see flecks of metal which came off the inside of the tubes..and it can indicate that the system is low on refrigerant... but the point is that you can not trust IT for showing when you have enough... get out the gauges and the thermometer in the vent if you think you are low... the only safe way.....

but this is the time to point out that Many cars DO NOT HAVE them anymore... because of their almost total uselessness and potential for wrong indicators....
Most can not be seen into well anyway... if you really like to use one.. put one which can be seen all the way through to the other you can point a light up from the bottom... available at specialty AC stores...

""Typically located on the top of the liquid line receiver drier in automotive

A/C systems, the sight glass provides a �look� inside the system.

The general rule is that when the sight glass is clear, the system is full of refrigerant. On the other hand, should there be bubbles visible in the sight glass, it could be a sign of a low refrigerant charge. Note, it could be a sign. That�s because under certain operating conditions, when there is a high demand for liquid refrigerant in the evaporator, some bubbles in the sight glass could be normal.

On current A/C systems, for the most part, the sight glass has been eliminated. That�s largely because of system design changes and the operation of the compressor�s cycling clutch that would cause bubbles to be seen in the sight glass even on properly working and fully charged A/C systems.""

""I have purchased a set of air conditioning gauges with a sight glass built in. Will this sight glass show foggy when the gauges are connected to an auto air conditioner with a low charge? Or will it only show foggy while adding refrigerant until it is full and goes clear? Just how is this sight glass used?

The sight glass on the gauges themselves is only used to visually verify that the liquid refrigerant is being charged when you charge on the high side of the system. It is also used in conjunction with a portable recovery machine to tell the technician when to switch the recovery machine from recovering liquid refrigerant to recovering vapor refrigerant.
It will NOT determine as to whether your piece of equipment has a low or high charge. The only way to effectively determine that is by comparing your gauge readings and the ambient temperature to a pressure.temperature relationship chart for the specific refrigerant. And it will NOT determine as to when the system is full. Again the only way to determine this with any accuracy is with a p/t chart and a mathematical formula.
Unless you are a technician that will be constantly working in the refrigeration world, you will not use the sight glass on the gauges themselves....""

Last edited by leathermang; 07-03-2011 at 12:21 AM.
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