Evaporator Coils Dirty Ice On Air Conditioner – It was a very hot day and I got a ticket to respond to a call for no cooling. The customer said there was ice on the air conditioner. The heating and cooling service operator instructed the customer to turn the AC off so the ice could thaw before I got there to figure out the problem. It needs to be thawed before any AC troubleshooting can occur. There are two main causes why the evaporator coil will freeze and cause ice on the air conditioner. One is decreased or no air flow and the other is a low refrigerant charge.
Evaporator Coils Dirty Ice On Air Conditioner - Causation
For low air flow the homeowner can possibly fix the problem depending on how serious the issue is. This problem can be because of dirty filters for the AC or heat pump. The problem is easily solved by thawing out the evaporator coil changing the dirty filter for the air conditioner or the heat pump system.
AC or heat pump systems equipped with a low refrigerant pressure switch will not freeze as the low air flow condition will cause a drop in refrigerant pressure and cause the low-pressure switch to trip the compressor thereby shutting off the compressor and preventing any freezing until the pressure increase closing the low-pressure switch allowing the compressor to run again. People with air conditioners or heat pumps that have low-pressure switches will likely need to call a technician but only after checking the air filters.
Other conditions that will cause low air flow include a bad blower motor, collapsed duct work, and a dirty evaporator coil. All three conditions will likely require the attention of a technician. The call I responded to on that day turned out to be a dirty evaporator coil. The customer failed to keep a filter in the system. The air handler was in a closet next to the kitchen. It turns out they kept the trash can next to the louvered door where the air handler was located. All the dust and dirt and some of the things that were thrown in the trash were found in the evaporator coil. That caused the reduced air flow and for the air conditioner to get ice on it.
Evaporator Coils Dirty Ice On Air Conditioner | Reduced Air Flow and Ice?
Why does the AC get ice on it when there is reduced air flow? The air in your home has moisture or humidity in it. Part of the process on air conditioning is to remove the moisture from the air. In air conditioning and heating engineers and engineering technicians use a psychrometric chart to determine the properties of air. This is the basis for calculating the size of AC or heating system you need to for the load or demand. The moisture in the air contains heat along with air containing heat. The heat in the moisture in the air is called Latent Heat and the heat in the air is called Sensible Heat.
Both forms of heat need to be removed from the air and that is what your air conditioner does. It removes the latent heat by dropping the evaporator coil below the dew point. When the evaporator coil is operating below the dew point the moisture in the air condenses. When moisture condenses it turns into a liquid and needs to be drained off through condensation piping or pump. This is why you see piping on your air conditioner that drains the water to the outside or see window units dripping water outside. It is the moisture in the air being drained outside after the evaporator coil condenses it.
The heat is also removed from the air (the sensible heat) by being absorbed into the cooler evaporator coil. The refrigerant in the evaporator absorbs the heat and carries it outside leaving you and your home feeling comfortable.
Evaporator Coils Dirty Ice On Air Conditioner - The Fix
When there is a lack of airflow the refrigerant temperature drops below freezing. The moisture in the air around the evaporator then begins freezing to the coil and any refrigerant piping leaving the evaporator going to the compressor (Technically the suction line). The solution to fixing the ice problem is to fix the air flow problem. The evaporator coil on that day was completely plugged up with dust and debris. When I arrived the ice was thawed and I quickly identified the problem. Because of how dirty the evaporator coils was I had to pull the coil from the air handler requiring a major operation on the AC system.
After removing the evaporator coil I took the coil to a car wash. I sealed off the refrigeration piping so prevent water or moisture from getting inside the piping. I then completely sprayed the evaporator with coil cleaner and got the nozzle for the car wash and spray the coil cleaned being careful to angle the spray as to not damage the coil fins. All the dirt and dust and trash were cleaned from the coil and the evaporator coil re-installed.
Evaporator Coils Dirty Ice On Air Conditioner - AC Back to Normal
After it was re-installed everything was returned to normal. The air conditioner was started and it cooled the home as a normal air conditioner would cool a home.The customer was instructed as to the importance of keeping a clean filter in the air conditioner system. If you have ice on your air conditioner because of dirty evaporator coils it is likely because someone failed to maintain a good air filter in the air conditioner.
There could possibly be other reasons for ice on your air conditioner and it will most likely require the services of a good HVAC contractor. Before you call make sure you check the air filter. If it is dirty change it and thaw out the system by leaving the fan on but the air conditioner off for several hours. Evaporator Coils Dirty and Ice On Air Conditioner go hand in hand so make sure your evaporator coils are clean!
How to Unfreeze the Air Conditioner
If your air conditioner is frozen or you find ice on the inside unit or the outside unit or piping then the best thing you can do is to shut the air conditioner off. By leaving it running you could cause damage to internal components to the air conditioner. The damage occurs from liquid slugging in the compressor. Compressors are designed to only compress vapor and not liquid refrigerant. When an air conditioner has ice on it there is a very good possibility the refrigerant is not vaporizing in the evaporator as it is designed to do. The next stop after the evaporator for the refrigerant is the compressor. Some compressors can take some slugging but long-term slugging will likely damage the compressor. Changing an air conditioner compressor is an expensive proposition.
If you have a heat pump you can turn it to heating mode and this will melt the ice from the heat pump. However, be aware that the melting may happen fast and this will overwhelm the drain. Make sure you keep an eye on it so you don’t cause water damage from the rapid defrosting of the coil. Even after you have defrosted or melted the ice from the air conditioner or heat pump you need to call a professional to check the unit. If the ice on the air conditioner was the result of a dirty evaporator coil then the coil will have to be cleaned before the system is put back into service. Other things should be checked once the air conditioner is running normally again. These checks make sure the problem does not reoccur and the system will be reliable for comfort reasons.
Other Causes of Ice on the Air Conditioner
There are other reasons you will find ice on your air conditioner. The evaporator coil being dirty is one of the conditions that will cause the system to freeze up. This problem is on the airflow side. There are problems on the refrigeration side that will also cause the system to ice up.
- Low charge of refrigerant because of an air conditioner refrigerant leak
- Problem with the refrigeration system
- The condensing unit will not turn off because of an electrical issue
- A dirty air filter
- A bad blower motor
- Collapsed ductwork
- Too many supply vents closed off
You can see from the list some of the problems with ice forming on your air conditioner are a result of poor airflow. The evaporator coil is designed for a specific amount of airflow. Without the designed amount of flow, the system will have problems and ice on your air conditioner can occur. A dirty evaporator coil that ices up is in the airflow category. The dirt blocks the airflow and the ability of the evaporator coil to absorb heat from the air. By checking and changing the air filter on a regular basis you can keep the evaporator coil clean preventing the problem of your air conditioner from icing up.
Evaporator Coils Dirty Ice On Air Conditioner
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