A micron reading measures absolute pressure in a refrigeration system during evacuation, expressed in microns of mercury (μmHg). This measurement indicates the level of moisture and non-condensable gases remaining in the system. Technicians use micron readings to verify that a system has been properly evacuated before charging with refrigerant.
Evacuation Standards
EPA regulations require evacuation to 500 microns or lower for most HVAC systems. For low-loss fittings and critical applications, evacuation to 400 microns or below is recommended. A micron gauge displays readings from 0 to 10,000 microns, with lower values indicating more complete evacuation and removal of moisture.
Practical Application
Proper micuation prevents acid formation, compressor failure, and reduced system efficiency. A system at 1000 microns still contains significant moisture that can react with refrigerant to form hydrochloric acid, damaging internal components. Technicians typically evacuate for 15-30 minutes using a quality vacuum pump rated at 6 CFM or higher to achieve acceptable micron levels before refrigerant charging.