Key Takeaways
- Proper evacuation is critical: Removing moisture and contaminants prevents premature system failures and ensures longevity
- 500 microns is the target: Use a micron gauge (not time or compound gauge readings) to verify proper vacuum level
- Core removal speeds evacuation: Removing Schrader cores eliminates 90% of restriction, dramatically reducing evacuation time
- Decay test validates success: Isolating the system and monitoring micron rise confirms absence of leaks and contaminants
Refrigeration System Evacuation Procedure Explained
Pulling a proper vacuum is vital to the operation and longevity of any refrigeration or air conditioning system. Moisture and other contaminants that are not removed can wreak havoc on system internals over time and cause premature failures.
Let’s walk through the complete process of achieving a proper vacuum that will set your system up for years of reliable operation.
Step 1: Start with Fresh Vacuum Pump Oil
Vacuum pump oil has the ability to grab hold of moisture and contaminants. New oil will significantly speed up the evacuation process.
When changing the vacuum pump oil, always change it while it’s warm. Warm oil holds more contaminants than cold oil, so changing it while warm helps remove maximum contaminants from the pump base. This simple step can cut your evacuation time dramatically.
Step 2: Remove Schrader Cores for Maximum Flow
Attach vacuum-rated Schrader core removal tools to the service fittings that will be utilized during the vacuum process and remove the Schrader cores. By removing the cores, you’re eliminating 90% of the restriction that slows down the evacuation process.
Important Note: Some manufacturers use service fittings with non-removable cores. Always verify core type before attempting removal to avoid damage.
Step 3: Skip the Charging Manifold
It’s strongly recommended not to pull a vacuum through a charging manifold due to multiple potential leak points. Instead, use a dedicated vacuum manifold, such as the Yellow Jacket SuperEvac, and attach it directly to the 3/8″ port on your vacuum pump. This eliminates unnecessary connection points that could compromise your vacuum.
Step 4: Use Proper Hose Sizing and Sealant
Attach vacuum-rated hoses (minimum 3/8″ diameter) to each core removal tool, then connect the other end of each hose to the vacuum manifold. Apply Nylog Gasket and thread sealant at every connection point. This ensures a leak-free process and prevents false readings during your decay test.
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Step 5: Position Your Micron Gauge Strategically
Attach a micron gauge to the system at the furthest point from the vacuum pump if possible. Alternatively, attach it to the tee of the core removal tool. Always mount the micron gauge above the system piping to prevent system oil from entering the gauge and causing malfunction.
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Step 6: Begin the Evacuation Process
Now you can start the evacuation. Always read the manufacturer’s vacuum pump start-up procedure before starting the pump to ensure proper operation and avoid damage.
Step 7: Monitor Micron Levels, Not Time
The evacuation process is not dependent on time or when your compound gauge hits 29.92″ Hg. Use the reading on your micron gauge to determine when a proper vacuum has been achieved. The industry standard target is 500 microns or below.
Step 8: Perform a Decay Test
Once you’ve reached your target vacuum, isolate the system from the pump and observe the micron gauge reading. This procedure, commonly called a “decay test,” validates your evacuation.
Reading the Results:
- Good system: Slight rise that levels off and flattens out, or no rise at all
- Problem present: Quick rise that continues climbing indicates either a system leak or remaining contaminants
Critical Note: Using vacuum-rated hoses and core removal tools with Nylog sealant at all connections is essential. Non-vacuum-rated equipment may leak during the decay test, mimicking a system leak that doesn’t actually exist.
Step 9: Add Initial Refrigerant Charge
After achieving vacuum success, add refrigerant slowly until the system pressure reads slightly positive. Know your micron gauge’s positive pressure limit to avoid damage during this process. Once you’ve reached positive pressure (below the gauge’s upper limit), reinstall the Schrader cores and remove the micron gauge.
Step 10: Complete the Charging Process
Add the remaining refrigerant charge according to manufacturer specifications.
Special Considerations for Solenoid Valves
When pulling a vacuum on a system with a solenoid valve, ensure the valve remains completely open throughout the evacuation process. Use a solenoid valve magnet like the Yellow Jacket model to accomplish this task.
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See It In Action
Check out this video for a real-world job site example of the complete evacuation procedure:
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Keep Learning
For more tips, tricks, and troubleshooting videos, check out my YouTube channel, and listen to The HVAC Know It All podcast here or on your favorite podcast app.
Happy HVACing!
