What is the proper procedure for pulling a deep vacuum below 500 microns after replacing a drier and capillary tube?

Pulling and holding a deep vacuum below 500 microns removes non-condensable gases (air) and boils off internal moisture introduced during brazing.

Required Tools & Equipment

• Vacuum Pump: Dual-stage rotary vane pump (3 to 6 CFM) with fresh oil.
• Digital Micron Gauge: Micron gauge mounted directly to the system (manifold gauge sensors are not precise enough).
• Valve Core Removal Tools (VCRTs): 1/4″ service port tools (if working on systems with Schrader valves).
• Vacuum-Rated Hoses: Large diameter (3/8″ or 1/2″) vacuum-rated hoses (avoid standard charging hoses with rubber gaskets).

1

Pressure Test the Braze Joints

Leak test at 150-200 PSI dry nitrogen before evacuating

Before connecting the vacuum pump, pressurize the system with dry nitrogen to 150–200 PSI. Check all fresh braze joints (filter drier, capillary connections, compressor stubs) with bubble solution or an electronic leak detector to ensure zero leaks. Bleed off the nitrogen down to 0 PSI.

2

Setup Core Removal Tools & Hose Connections

Remove restriction to airflow

Remove the Schrader valve cores using Valve Core Removal Tools (VCRTs) if service access ports exist. Connect heavy-duty vacuum hoses directly from the VCRTs to the vacuum pump inlet. Mount the digital micron gauge on the side port of the isolation valve—never directly on the pump inlet.

3

Initiate the Pull-Down

Run until reading drops well under target

Start the vacuum pump and open the isolation valves. Monitor the micron gauge drop:

• Atmosphere to 5,000 microns: Rapid drop (air removal).
• 5,000 to 1,000 microns: Slower drop (water moisture inside the lines begins boiling into vapor).
• Under 500 microns: The target range. Continue pulling down until the reading reaches 250 to 300 microns to provide a buffer for the decay test.

4

Perform the 10-Minute Vacuum Decay Test

Isolate the pump and observe pressure rise

Close the valve on the VCRT/manifold to isolate the system from the vacuum pump, then turn off the pump. Observe the micron gauge for 10 minutes:

• Pass: The pressure rises slightly and levels off below 500 microns.
• Moisture Present: The pressure continues to rise steadily above 500 microns and levels off somewhere between 1,000 and 2,500 microns. (Solution: Break vacuum with dry nitrogen, sweep, and pull again).
• Active Leak: The pressure keeps rising continuously past 5,000 microns up to atmospheric pressure. (Solution: Re-pressurize with nitrogen and locate the leak).

5

Break Vacuum with Refrigerant

Prevent air ingress during charge

Once the decay test passes, purge your refrigerant charging line before opening the refrigerant bottle, and introduce the factory-specified refrigerant charge by weight while the system is still under vacuum.

Critical Vacuum Best Practices

1. Change Vacuum Pump Oil: Contaminated or saturated pump oil will prevent the pump from pulling below 1,000 microns. Change the oil if it appears cloudy or dark.
2. Thermal Vacuum Sweep (For Stubborn Moisture): If moisture is trapped in the oil or fresh joints, use a heat gun to gently warm the filter drier, evaporator, and suction line while pulling vacuum to speed up moisture vaporization.
3. Never Use Compressor to Evacuate: Using the refrigerator’s own compressor to pull a vacuum will overheat the motor windings (which rely on cold refrigerant gas for cooling) and can cause dielectric arcing across internal electrical terminals.