There are many questions about air conditioner issues with the most common being that it isn't cooling properly. Among the typical answers are low Freon and the standard diagnosis for low Freon is ice on the large copper pipe at the outside compressor. From my understanding the small copper tube is the high pressure side with Freon that has been compressed to a liquid. When this liquid is allowed to boil in the inside evaporator things cool down. Conversely the large copper pipe is the return line from the evaporator sometimes referred to as the suction line or low pressure side. So my question is: under low Freon conditions how can the suction line freeze up? Intuitively I would thing with low Freon the entire cooling ability would be below normal causing the evaporator to not produce as much cold air. A side effect of all this, I would expect the suction line to be warmer that normal. Why does the suction line freeze up under low Freon conditions? See the image in this question for a great diagram of an HVAC system:

What's the most common cause of A/C refrigerant lines freezing? Chlorodifluoromethane, also known as R22 refrigerant has a boiling point of -40°F at 0 psi. As you increase the pressure of the refrigerant, the boiling point also increases. portable air conditioning unit self evaporatingAt 68.5 psi, the boiling point of R22 is 40°F.10000 btu window air conditioner with heat In a normally functioning system, the refrigerant is sent into the evaporator at about 55-65 psi. the nest.unitec.ac.nzWhich means that the boiling point will be above the freezing temperature of water. The refrigerant absorbs heat from the air passing through the evaporator, boils, and flows on down the line at a temperature above the freezing point of water.

The refrigerant will likely be below the dew point, however, so there will be condensation on the line. If the pressure in the system drops, the R22 might be entering the evaporator a bit lower than the typical pressure. In this case, the boiling point of the R22 will be below the freezing temperature of water. As the warm moist air moves over the evaporator, the moisture condenses and freezes on the coils. Ice will start to form at the beginning of the evaporator coils, and slowly creep along its length. The ice will act as an insulator, so the refrigerant in the line will not be able to absorb the heat it needs to boil. This causes the refrigerant to boil off further along in the evaporator, which forms more ice further down the line. This process continues all the way along the line, until the entire evaporator and suction line are covered in ice. Once the refrigerant levels get too low, there's not enough refrigerant in the system to freeze the line. So eventually if the system has a leak, this behavior will stop and you'll simply get no cooling at all from the system.

NOTE: I could be completely wrong here. This is based on my limited knowledge of air conditioning systems. I am not an expert in thermodynamics, fluid dynamics, chemistry, or HVAC. Superheat of the refrigerant should take place toward the end of the evaporator coil. If the the system is low on "freon" and the metering device is not a txv then the freezing up could very well occur because the pressure drop is not very well controlled. Non txv systems rely on a near perfect balance or charge of refrigerant. An overchared system can have a similar effect.Browse other questions tagged air-conditioning freezing or ask your own question.Low refrigerant or refrigerant undercharge effects on air conditioners & heat pumps or other HVACR equipment: This article explains the symptoms of and problems caused by not enough refrigerant in cooling equpment. Refrigerant charge quantity for air conditioners & heat pumps: This air conditioning repair article series discusses the the diagnosis and correction of abnormal air conditioner refrigerant line pressures as a means

for evaluating the condition of the air conditioner compressor motor, which in turn, is a step in how we evaluate and correct lost or reduced air conditioner cooling capacity. We explain how overcharging or undercharging of refrigerant in an air conditioner or heat pump is detected and we list the effects of overcharged or undercharged refrigerant. We also explain the various causes of liquid slugging a compressor motor. Effect of too little refrigerant in the system When we undercharge an air conditioner, heat pump, or other refrigeration equipment Bottom line about undercharging refrigerants: For residential equipment such as air conditioners, heat pumps, refrigerators, freezers, to work properly you must have exactly the correct charge in the system. At FROST BUILD-UP on AIR CONDITIONER COILS we also explain that in a properly tuned and adjusted refrigeration system there will be liquid refrigerant found all the way to just at the end of the evaporator coil - this gives us maximum cooling efficiency of the equipment.

The effect of too much refrigerant in the system - overcharging, over-metering, or other high refrigerant pressure situations are detailed at EFFECTS of OVER CHARGING of REFRIGERANT If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS. See How to determine the cooling capacity of air conditioning equipment if the system seems to be working but is inadequate to cool your building. Continue reading at TEV INSTALL & REPAIR or select a topic from the More Reading links or topic ARTICLE INDEX shown below.Refrigerant (sometimes referred to by the brand name Freon) is an important part of your . So if your refrigerant is low or improperly charged, it can have a big impact on your comfort and electric bills. While you won’t be able to tell every time there’s a leak (that’s what regular A/C maintenance is for), here are 3 signs you’re missing enough refrigerant for it to matter. If your air conditioner is low on refrigerant or the refrigerant is improperly charged, your air conditioning system will have to work harder.

This translates to higher electric bills for you. Check your electricity usage and compare it to past years and past months. Of course, there could be other reasons your bills have gone up (like rate increases). But keeping an eye on your overall electric usage is important because it can help you spot problems (like low refrigerant) before they get bigger. If you notice a spike in your energy bills and think your air conditioner is the culprit, call us and we’ll take a look to see if low refrigerant (or something else) is the problem. Does your home take forever to cool off in the summer? Does the air blowing out of the vents seem warm? The problem could be low or improperly charged refrigerant in your air conditioner. Without the proper amount of refrigerant, your air conditioner isn’t able to remove as much heat from your home’s air as it normally would. This can make your home very uncomfortable. This problem could also be caused by something else, but you should have a professional air conditioning repair company take a look so they can identify the problem and you can enjoy cool air in your home again.