# How to Use a PT Chart for R12
Pressure temperature (PT) charts are used in heating and air conditioning (AC) to give the proper ratio of pressure and temperature inside a unit. If you have an air conditioner that has a low charge or is overcharged, you can rebalance the system using a PT chart. There are different types of refrigerant used in residential settings. R12 is one of the most common refrigerants used for residential heating and air conditioning.
Things You'll Need
- PT chart
Instructions
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1
Connect a gauge to your refrigerator’s low side service port. The AC unit will have two pipes coming off the back of the unit. The low side is the bigger of the two pipes. Use your fingers to remove the service port cap and screw the gauge into place.
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2
Take a reading from the AC gauge. The needle on the inside of the gauge will signify this. It should be pointing to a number. This is the pressure on the unit.
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3
Run your finger down the “R12” column on your PT chart until you reach the pressure. Read the “Temperature” translation next to the pressure text to get your temperature.
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1
Air Conditioners
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