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Old 07-04-2012, 05:59 PM
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Correct Freon Levels - the easy way

Many of us do not have access to an expensive machine to ensure you have the proper freon chage in your vehicle. With the help of a few tools and a smart phone app you can insure you have not under OR overcharged your system.

You will need:
A source of freon (r12/r134a - never mix the two)
Inexpensive manifold gauge that will draw from the freon source
Multi-tester that has a "K" type contact thermocouple (thermometer)
You can get the above two at Harbor Freight Tool for around $90.00
On your smart phone (apple or android) download the app "PT Calc"

A basic knowledge of component locations on the AC system.

Connect the manifold to the freon source and open the lines while NOT connected to the vehicle to flush out air and fill the lines with freon then shut off the valves. You will only need to connect to the low side/suction side of the system. (the blue hose)
Start the vehicle, turn on ac to recirculate and open the windows with the fan on high. Ideally the vehicle should be warmed up and outside.
As the system is running look at the low side PSI and write it down.
Use a small piece of foam door jamb insulation to hold the contact thermocouple to the freon line just as it exits the evaporator (at the firewall). The insulation will protect you from a false reading from your finger or engine heat. BE SURE to get the exit pipe - this is the one that goes to the accumulator drier on most Ford's.
Write down the temperature.
On your smartphone app PT Calc select the screen called "Superheat" Select the type of freon used (usually 134a). Enter the psi and temp.
If your system is filled just right the Superheat should be about 3 or 4 degress F. If it is higher add 1/4 lb of freon (about 4 oz), kick up the RPM for a minute, let things settle for a minute and re-check temp and psi and plug them back into the app.

Even 1 psi or 1 degree of temp will change the superheat calculation so try to be as accurate as possible. Put the temp probe right where the pipe exits the evaporator, or as close as possible. Your will have to hold it there for about 30 seconds to get a good reading.

Do not take the psi reading with the freon source valve open. Close the blue valve on the manifold so that you only get system pressure.

If your vehicle has a TXV or thermal expansion valve instead of an orifice tube you can still use this method. Be sure to place the temp probe as close to the firewall as possible. In a TXV system the drier is on the "high" side of the system close to the condensor. This pipe will feel hot as it goes into the fire wall.

Hope this helps. Remember - an overcharged system will DESTROY your compressor. This is a classic case of more is NOT better. Your system needs a fine balance of freon, not to little, not too much.
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