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Old 08-13-2002, 07:51 PM
Don Hicks
Posts: n/a
Recharging Air Conditioner System With Small Can Of R134a

190E 1995

The R134a goes into which value "High Side or Low Side? How can I determine which side is the high side? Will be using the small can of R134a.

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Old 08-13-2002, 08:42 PM
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Join Date: Apr 2000
Posts: 166

I do not mean this as a put-down, but judging from the questions you have asked, you are about to flirt with a possible disaster.

Without gauges and some knowledge of a refrigeration system, you will be much better off paying someone to tend to this for you. These things have been known to blow up in peoples' faces.

Hope this helps you make a prudent decision.
1979 240D
165,000 miles
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Old 08-14-2002, 12:30 AM
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Join Date: Oct 2001
Location: California
Posts: 287
With the air conditioner running, the line that is cold is the low side. You put R134a in the low side. The high side is very hot, you might burn your fingers if you touch the high side line. Do not mess with the high side.

You need a pressure gauge to determine the air conditioner's state of charge. Walmart and Kmart have a recharging kit with a low side gauge for $25. Without this gauge, you risk the chance of over charging the system.
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Old 08-14-2002, 05:24 AM
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Burning your hands could be the least of your problems if you charge to the high side. The can will possibly explode.

I highly recommend that you don't charge based solely on a two bit low side gauge from Wal-Mart. Refrigeration is definitely not a DIY project unless you do a little study and have the right equipment.

There is an excellent book available at that is a basic training manual for a/c. They also have equipment and supplies that you might need. Another excellent source is You can access these and a great discussion board where your a/c questions will be answered by pros at;

Please be careful and don't hurt yourself or destroy your air conditioner.

Good luck,
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Old 08-14-2002, 05:38 PM
csnow's Avatar
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Join Date: May 2002
Location: Mass
Posts: 1,127
Agree that education is a good thing, but just to add to what has been said:

While the gas goes in on the low side, it is the high side pressure that should be measured to determine when the system is fully charged (with a partial recharge). This value is specific to your AC system, and varies substantially based upon ambient temperature.

That is one reason why it is better to use a real manifold gauge set, as Larry mentioned.

1986 300E 5-Speed 240k mi.
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