In a chilled water system with an air-cooled condensing unit on a roof during cold weather, what type of protection is used?

• A. Weatherproof enclosure
• B. Heaters
• C. Insulation blanket
• D. Air limiting device

Answer: (D)

The key idea is that in very cold weather a roof-mounted air-cooled condenser can be harmed by too much cooling of the refrigerant side. An air limiting device is used to throttle or regulate the amount of air flowing across the condenser so the system doesn’t over-cool the refrigerant and drive pressures down too far. By limiting airflow, the device helps maintain safe pressure and lubricant conditions for the compressor, reducing the risk of improper cycling or damage when outdoor temperatures are low. Other protections like a weatherproof enclosure, heaters, or an insulation blanket address different concerns—protecting the unit from weather, preventing freezing of pipes, or reducing heat loss—without specifically controlling condenser air flow to preserve safe operating pressures in cold weather.