Why does low refrigerant cause freezing

There are a few reasons that air might not be flowing efficiently. The most common problem is a dirty air filter, which is pretty self explanatory, a dirty air filter means less air flow.

If you are running your AC unit continuously, we recommend replacing or cleaning the air filter once a month. Other problems include blocked or closed ducts and vents, a faulty fan and dirt on the evaporator coils. Evaporator coils need regular cleaning, we recommend once a season.

This causes a drop in pressure in the evaporator coil which then allows moisture in the air to accumulate and freeze on the coil.

Inside of your home is an evaporator unit with coils. The refrigerant passes through a narrow opening at which point it expands on the other side as a gas think of a spray can.

The process of converting to a gas absorbs heat from the coils which have the return air passing over them on their way into the ducts. When the refrigerant levels run low, there are different ways of understanding this impact. I've seen it described that there's less refrigerant there to absorb heat from the home and the closed loop gets too cold after exhausting the little heat it does gather outside.

But to me it makes more sense to imagine the effect of the pressure drop in the evaporator coils. The more the pressure drops in those coils, the more extreme the temperature difference as the refrigerant expands to a less and less dense gas. But keep in mind that you still have less refrigerant moving the heat, so while the refrigerant that remains is colder, it's also less efficient. Additionally, that lower temperature refrigerant comes with a downside. Once the coils drop below the freezing point, moisture in the return air that's passing over the coils doesn't just condense and run out the condensate drain think of a cold drinking glass on a hot humid day, your coils look like that normally.

Instead, that condensation freezes until it's a solid block of ice and no air can pass through. This same problem can happen if you run your HVAC when the outside temperature is too low, so much heat gets removed by the outdoor coils, that when the refrigerant runs through the evaporator is gets below the freezing point.

This is why it's very important to not oversize an HVAC for your home, it will cool the air too quickly and result in freezing, and it will run for very short periods of time but not remove enough moisture due to those short run times, leaving you very humid in the summer.

Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Why do the evaporator and suction lines freeze when there is low refrigerant? Ask Question. Low Refrigerant When your air conditioner is low on refrigerant, pressure drops in the system and the temperature drops with it.

If you suspect a leak, call an HVAC technician immediately to diagnose the problem. Faulty Thermostats Malfunctioning thermostats or thermostats that are set too low can force an air conditioner to run constantly, causing the temperature of the condenser to drop below freezing.

Drainage Problems If you live in a humid climate, a lot of water vapor is turned into condensation within the air conditioner. FL LIC. As the moist, warm air from your house moves over the evaporator, the moisture will condense and freeze on the coils and ice will begin to form! You might not notice a change in the performance of your system with minor frost, but too much ice will affect the airflow.

Eventually, the ice will act as an insulator and prevent the air conditioning system from functioning properly, and the R22 refrigerant will evaporate faster. If your system does not cool anymore, your AC potentially has water damage. We recommend having an HVAC professional inspect your home as soon as possible to repair it.

Check and replace your air filters first. Even if your air filters are clean, poor airflow could still be the problem. Inspect all of the air vents in your home, holding your hand in front of them to feel for air leaking from the sides of the grate. The third most common cause of AC freezes is a dirty air conditioner coil.