******This is for educational purposes only. Handling, recovery and installation of refrigerant should be done by experienced, licensed technicians.******
The first thing you want to do is very that the problem you are having is caused by failure in the sealed system or something else. There are a multitude of checks you can do but we'll take the fast track.
1) Confirm that the compressor is running. Usually when the machine is low on freon, the compressor will run but not generate a lot of heat.
2) Remove the rear wall of the freezer and check the evaporator coils. If the coils are mostly aluminum, with a small section of frost or ice, then you have a freon issue, if completely covered in frost or ice, stop this route and diagnose for defrost issues.
3) Verify all fans are running, coils are clean.
Okay, if your check list all check good, then move forward with the sealed system diagnosis. The tools you'll need for checking are as follows:
1) HVAC guages, not automotive.
2) A piercing valve, some machines have an access port already, but most don't. I use a bpv-31.
WIth the machine running, locate the suction line coming from the compressor, it will be the bigger of the two. The smaller line is called a discharge line and is part of the high side of the freon loop. DO NOT MESS WITH THIS LINE. Once located, install the piercing valve, pierce the line, attach your gauge using the blue line, and open the valve. You'll now be able to see the pressure in the machine. You'll notice the outside numbers on the blue gauge, most in blue, the lower portion in green going to 30. The green means a vacuum. Your freon level should be anywhere between 5 and 10 on the blue side.
If your number is in the blue but way past 10 with the compressor running you have a restriction and you should stop and call a tech.
If your number is in the blue but below 5, you may have a micro leak.
If your in the green, the machine is in a vacuum and has a significant leak.
********* Note that knowingly adding freon to a machine with a leak without first repairing the leak is a federal offense, and carries a major fine, like $25,000.*******
Now, lets say the machine is in a vacuum, like at -10, or 10 in the green, we'll go to the next steps. If your gauges read like 30 in the green stop because thats a major leak. The tools you'll need for the repair are as listed:
2) valve (already installed)
3) vacuum/recovery pump
5) Freon can piercing tool since your only going to be able to but the small cans without epa certification.
6) recovery bag
Okay, turn the machine off. Leave the gauges connected and connect the yellow line to the recovery pump, with the pump connected to recovery bag. Turn on and open manifold (gauges) valve and vacuum all the old Freon out of the machine. Let the pump run for about 30 minutes.
Next, close the manifold valve, then turn the pump off. The needle on the gauges should be at 30 in green and not move. If for any reason the needle moves upward toward the 0 then you have a major hole somewhere and it has to be sealed.
If the vacuum holds, take the yellow hose off the pump, pierce the Freon can with the clamp (tool) and connect yellow hose to it. You'll want to unscrew the yellow hose at the manifold for a brief second to vent the air out, leaving only Freon. You don't want any moisture in the sealed system.
Now this is the part where you should have Freon scales, or a graduated cylinder to measure the amount of Freon. On the sticker on the inside of the machine, you'll see the amount that goes in the machine. Most cans are 10 oz . Most machines don't use that much, and over charging a machine will cause it not to cool.
Add your Freon by opening the manifold valve, and be sure the piercing valve is open as well. Get as close to the amount as possible. When done, close the manifold and watch the pressure to make sure it stabilizes and doesn't drop down. With the machine off it will be pretty high.
Plug the machine in and leave the gauges connected and watch the pressure on the gauge, it will drop, your concern is that the needle finally rest between 5 -10 in the blue.
If this is the case, Close the piercing valve, remove the gauges and your done.
******* Remember this a short hand version of Freon installation. This is nothing compared to actually having the right equipment, training and experience.
If you need further help, I’m available over the phone at https://www.6ya.com/expert/jason_4570d45317834dd3