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During the cooling mode of the Air Conditioning system, a fan draws warm air from inside the home through a filter and the furnace and then over the evaporator coil. As the air passes over the coil, much of the moisture the air possesses is condensed and runs off into a drip pan where it is drained away through the drain lines. This process occurs because as the warm air passes over the coil, it is quickly cooled and can no longer hold the same amount of moisture as it did when it was warm. The refrigerant inside the evaporator coil enters as a liquid and once the warm, filtered air is passed over it, the temperature of the air is lowered. From here, the refrigerant carries the warm air as a gas to the outside compressor where the vapor is compressed and passed through the condenser's coil. This process is much the same as what happens to a glass of cold water on a hot and humid day.

Proper Coil Sizing

The coil size determines the major balance between dry and wet heat removal. The coils remove dry heat (temperature) and the wet heat (humidity). The coil size determines this ratio. The larger the coil in size, the lower the humidity removal. In many cases, a smaller coil can increase the humidity removal by 30% to 40% resulting in greater dehumidification. After extensive research, we have found that having a matched or oversized evaporator coil will not control humidity enough. Rather it increases the humidity level in the home, especially at night. The reason is that the evaporator cannot get cold enough to properly dehumidify the air, causing your air to feel sticky and humid.

Adjustable Thermal Expansion Valve

If you're A/C system is removing the maximum amount of humidity, mold will rarely appear in your home. Without an expansion valve the entire system performance is compromised. Humidity control is usually poor at best, however adding an expansion valve to an existing system can often improve performance, reduce operating cost and extend the life of the overall system. When an expansion valve is installed, we include a sight glass in the small liquid line to provide a means of checking the refrigerant level.

An expansion valve, properly sized and installed correctly, adds exactly the right amount of refrigerant to the coil. This occurs under all conditions and keeps the coil as cold as possible, resulting in maximum humidity removal, a more comfortable environment at a higher temperature with lower operating cost and longer system life with less breakdowns.

Central City Air Custom 2-stage Coil

The 2-stage coil is specifically designed for use with two-stage or split capacity systems. Used in conjunction with the two-stage, condensing unit, or zoning system, your comfort system will offer improved cooling and dehumidification in both stages. A standard, single-stage, evaporator coil and two-stage condensing unit cannot do this. This is because the evaporator coil becomes severely oversized when the condensing unit runs in low-stage. For example, a 4-ton, condensing unit decreases to 2-tons of capacity in low-stage with a 4-ton evaporator coil. This causes the system to lose most of its latent heat (dehumidification) removing capacity. Our custom, two-stage, evaporator coil, adjusts its capacity according to the load stage the condensing unit is operating in.


Diagram of a custom 2-stage coil

Diagram of a custom 2-stage coil. Click here for more information on our custom coils

Further Reading

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