2006 LGT A/C Coils Freezing up and blowing condensation

[discojon]

The inside coil is routinely freezing up and blocking air flow from the fan now. It began a few weeks ago by blowing condensation out on humid mornings, but now is routinely freezing and blocking all air flow. When it happens, I just switch off the A/C button for a few minutes until it melts from ambient air flow. A/C blows plenty cold and the drain line is clear. I have a set of gauges and will check the levels this weekend. I'll also check the filter. Any other thoughts on what to look for?

[DrD123]

There is a thermocouple/thermistor that is pushed into the fins on the evaporator - that is used to monitor the temperature and let the car know when to cycle the compressor on/off - if the compressor is run too long, and the air coming in is humid, it will freeze up. Could be that has failed or come loose. (p/n is 73540AG030)

[discojon]

Thanks. I'll check it. I put the gauges on and both high and low sudes were under the recommended pressures. I added some refrigerant and that seemed to help out so far.

 

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[Saltysubie]

I've seen a few frozen evaporator coils. The leading causes are:

 

1) Reduced airflow across the evaporator coil. This reduces the heat absorption through the evaporator. The heat transfer rate is directly proportional to the mass airflow rate. Then, because the condenser side is working to reject heat at the same rate as it was before, an imbalance of heat through the system occurs, dropping the overall system's refrigerant pressures/saturation temperatures to the point where the refrigerant in the evaporator is at a temperature well below the dew point of the air blowing across it and it freezes moisture from the air onto the evaporator coil. It is literally a snowball effect after that, because the ice formation further reduces airflow and compounds the problem.

 

2) Low refrigerant charge. In some ways, similar to the issue above. With a low charge, the overall pressure within the system will be lower. With a lower refrigerant pressure in the evaporator, it will have a corresponding lower saturation temperature. This low refrigerant temperature can be so low that it freezes the moisture in the air when it contacts the coil. The, the snowball effect again happens as airflow is reduced from frost buildup.

 

Like DrD123 said, if there is a controls component that is keeping the compressor running excessively long, especially if the fan speed is reduced, it is possible to freeze a coil too. But this scenario takes will typically take a longer time before the coil starts to frost up. So, I would first check for anything that reduces evaporator airflow and second, check the refrigerant pressures (you need a chart for ambient vs indoor temperatures vs refrigerant temperatures, in order to know what to look for on your gauges). I'm guessing you already knew that. After that, I'd look at controls issues.

 

 

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