Why there are ice on the evaporator coil of my air con?

Question

Recently, my aircon was not cold and I discovered a lot of ice on the evaporator coil (too much condensation).When I called service man to check he just top up the gas and it was ok.I am puzzeling why the ice form when the gas amount was lesser.Is it due to more pressure difference of high side and low side?

Answer 1

Restricted air flow. Make sure the vanes are clean. Use a vacuum or a brush to clean the vanes.

Answer 2

OK, I just answered a version of this question for you but didnot really get into the specifics. I can see you need more than just "because that the way it is."

First I am going to assume that your A/C uses R-22. Most of them do.

In an evaporator, the refrigerant (it is not always a gas) goes from high pressures in a liquid form to low pressure. Usually an expansion valve will cause the pressure drop. When the liquid goes to low pressure, it evapoates (that is why it is called an evaporator). The temperture at which it evaporates is different for different pressures!

With R-22, your normal suction (the pressure of the evaporator) is around 70 psi. This corrisponds to a temperture of about 44 degrees. Now, the entergy to cause it to evaporate has to come from somewhere. In an A/C it comes from the air that is blowing over the coils. This lowers the air temperture.

If the pressure in the evaporator falls below 54.2 psi, then the refrigerant will evaporate at 32 degrees. Still no ice there becuase the air will heat it up, but if the pressure falls to low, then ice will form on the evaporator.

When your refrigeant gets low, the pressure in the evaporator will also get low.

This is still a simplified explaination, but I hope it get's the idea across.

Answer 3

It is puzzling, but there is a good explanation.

The refrigerant (in liquid form) doesn't just freely evaporate inside the evaporator coils. A small valve controlled by a thermostat restricts the flow of liquid refrigerant. This is the expansion valve. When there is plenty of refrigerant, it lets some liquid into the evaporator. That evaporates and cools the coils. When the coil temperature gets near freezing, the expansion valve shuts off the flow of liquid refrigerant, so you get condensate (water) on the outside of the coils instead of ice.
Then as the evaporator warms up a little, more liquid ref-gt is let through.
When the system is too low on refrigerant, it begins to stop cooling. The gas portion of the refrigerant is no longer hot as it is when the system is properly charged. That gas portion can pass through the expansion valve freely and cool the coils too much. Once frost starts accumulating, it insulates the coils and starts a vicious cycle that ends with them completely iced.

To summarize, it is because you are now circulating mostly cool gas, which can't be thermostatically controlled as the liquid is.

I like Walking Man's explanation better than mine. I wonder if he might elaborate more on the expansion valve's role in this.

Answer 4

Top off the gas? You mean refrigerant? The only thng I could think of that would cause more ice on the coil is because like you said, the difference between high/low is great, and the coil is working too well, or there are too much humidity in the environment where the coil is functioning.

XR

Answer 5

I don't think the "top-ff" had any thing to do with the problem. It happened to me when the outside temp dropped low. The inside coil got so cold that it froze the condensate before it could run off.

Answer 6

Your ACU filter is just dirty and dusty. I experienced that with my unit in our living room. Clean it and have a regular maintenance check.

Answer 7

you got that right, remember that your A.C.unit doesn't maks cold it removes heat