When evacuating a _______ compression system, the vacuum pump should be capable of pulling 500 microns (29.90\" hg.) of vacuum.

• A. Air
• B. Vapor
• C. Liquid
• D. Refrigerant

Answer: (B)

In a vapor-compression refrigeration system, the goal of evacuation is to remove air, moisture, and other non-condensables from the refrigerant path before charging. Pulling a deep vacuum, about 500 microns, ensures that moisture is boiled off and pumped out and that non-condensables don’t linger to cause high pressures, poor oil return, or corrosion once the system is charged. The description specifically refers to a vapor-compression system because this type of system relies on refrigerant in vapor and liquid phases, and removing these contaminants is crucial for proper operation. Evacuating to this level helps ensure the system is dry and ready for refrigerant charging. The other options don’t describe the type of system being evacuated in this context: air, liquid, or refrigerant systems aren’t the category addressed by this evacuation guideline in a vapor-compression scenario.