Technicians who work on central air conditioners and heat pumps use manifold gauges to find the Freon pressure and indirectly the evaporator and condenser temperatures by connecting to access fittings on the unit. These gauges have hoses of various lengths and when they are removed from the access fittings some Freon is retained in the hoses. This is not a problem with systems that contain pounds of Freon since the amount retained in the gauge manifold hoses is a small percentage of the correct charge.
Household refrigerators and freezers usually do not have access fittings. This is not necessarily a bad thing. Some refrigerators work with as little as eight ounces of R-134. Connecting gauge manifold hoses to the high-side of the system could leave a large percentage of the charge in the hose when it is disconnected. To connect to the system and read Freon pressure one must use a piercing-valve, which clamps on the refrigerant tubing and punctures a hole to allow pressure readings. These valves must be left in place afterwards and provide a place for refrigerant to leak if they are not clamped tightly or if the seals deteriorate over time.
I only install piercing-valves on a refrigerator or freezer as a last resort. Despite the common belief that almost every refrigerator problem is due to the lack of Freon that is just not the case. Most refrigerator malfunctions are caused by the failure of electrical components. An insufficient Freon charge is one of the last things I consider when troubleshooting a refrigerator that does not cool. FREON LEAKS OUT; IT DOES NOT WEAR OUT. It is unlikely that your refrigerator will suddenly start leaking just sitting in your kitchen UNLESS it is manual defrost and you recently removed the ice from the freezer compartment by using a knife, screwdriver, chisel, or pry bar and punctured the aluminum evaporator coil or an incompetent service person installed piercing-valves that are leaking.
Conditions which may seem like lack of Freon but are not:
Evaporator fan not running which ices up the evaporator and raises freezer and fresh-food compartment temperature.
Condenser fan not running which raises temperature of freezer and fresh food compartment.
Dirty condenser which raises temperature of freezer and fresh food compartment.
Defrost problems (if automatic defrost) which ices up evaporator raising temperature in freezer and fresh food compartment.
Old compressor with worn valves that raises evaporator pressure and temperature.
Worn door seals that allow hot air to leak into the freezer or fresh food compartment (Note: Some Haier refrigerator doors won’t seal even when new.)
Clogged filter dryer or capillary tube which keeps the Freon from circulating properly.
All the above conditions make the compressor run continuously or almost continuously, but so does a lack of Freon. The compressor runs continuously because the refrigerator cannot reach the set-point on the cold-control. Keep in mind that if you set your cold control to mid-range and it can’t cool to that setting, turning it to max (which asks it to make the temperature even colder) does absolutely nothing.
The fastest and easiest way to find out if the unit has Freon is to turn it off and listen. When a compressor pumps Freon the evaporator pressure decreases and the condenser pressure increases (thus we have a high and low side of the system). When the compressor stops running the refrigerant pressures in the system slowly equalizes through the capillary tube. This can take several minutes. Turn the cold control to the off position and put your ear to the side of the unit. If you hear hissing and gurgling noises the unit has some Freon, which is equalizing through the capillary tube (it may not be a correct charge). If you hear nothing, the unit contains little or no Freon or has a clogged filter-dryer or cap tube OR the compressor is running but not pumping (worn or broken valve). None of these conditions are as likely as having a defective fan, dirty condenser, or defrost problem.
If you hear the hissing and gurgling of Freon, but the unit won’t freeze ice or the ice cream is soft, unplug the refrigerator and remove the cover from the evaporator. The evaporator is in the freezer compartment near the evaporator fan. Each model is different so spend a few minutes to figure out how to expose the evaporator. Some GE and Magic Chef models place the evaporator in the bottom of the freezer compartment which makes repairing the defrost system difficult. On an upright freezer the evaporator may be tubes that are part of the shelves so nothing needs to be removed. Chest freezers have the evaporator beneath the inner lining and usually cannot be exposed.
If you remove the panel covering the evaporator and find a big block of ice, you either have a defrost problem or the evaporator fan wasn’t running. Sometimes a defrost problem will form so much ice that the fan can’t run. Thaw the evaporator and see if the fan will run before condemning it.
If the evaporator is not encased in ice arrange the cover so that the unit can be restarted. This may be difficult if the fan is attached to the panel. The capillary tube is a small copper tube entering the evaporator. The suction line at the evaporator outlet will be much bigger.
Liquid refrigerant (freon) entering the evaporator begins to boil into a gas because of the sudden drop in pressure created by the compressor. This change of state absorbs heat. The temperature inside the evaporator coil may be -20 degrees F. This will condense and freeze moisture in the air in contact with the coil (which is why we have to defrost). If there is freon boiling inside the evaporator this frosting will occur within minutes. So if we run the unit with the cover off the evaporator and no frost forms we can know that there really is no freon or the the system is clogged. If the unit runs for several minutes with the door closed and the freon charge is correct, the frosting should form all along the length of the evaporator.
Other signs of the presence of freon is heat in the condenser. If the unit has been running for several minutes and the condenser is cold, there is either little or no freon or the system is clogged or the compressor is not pumping.