Arkansas HVACR NewsMagazine January 2026

HVACR NewsMagazine January 2026

Tech News

1. The Graph Tells the Story: Triple Evac Didn’t Change a Thing

3. Vacuum Pumps Don’t “Pull” Moisture Out. Pressure Pushes It. This is the physics most techs never hear: • Vacuum pumps create a low-pressure zone • The system must PUSH vapor toward the pump • In cold systems, frozen moisture produces almost no push

Look at the evacuation slopes: • Every pull follows nearly the exact same slope • Every decay rises the same way • The system tails off above 1,000 – 2,000 microns • It NEVER stabilizes (flattens out)

If triple evacuation worked, each pull would look significantly deeper, and the isolation would improve. You can see that each time it was pulled back down, the slope at the bottom mirrors that of a long pulldown. The curves are identical. That means nitrogen sweeps had almost zero effect on drying. The limiting factor was TEMPERATURE, not technique. 2. The System Hit 135 Microns, But It Was Still Wet! This is the part that surprises techs: A good vacuum rig can overcome the low vapor pressure and force a system down to 135 microns even when moisture is still present. Deep vacuum alone doesn’t prove dryness. Why? Because the physics of vapor pressure creates a trap that most technicians fall into.

A vacuum pump does not reach into the copper tubing and pull molecules out. In strict physical terms, “suction” does not exist. A vacuum pump merely creates a mechanical void at its inlet. The evacuation of a refrigeration system is entirely dependent on kinetic molecular theory, which describes gas as a collection of particles in constant, chaotic motion. The vapor pressure of ice at 28°F is approximately 3,800 microns .¹ But here’s the trap: as sublimation cools the ice further, that pressure collapses. At -40°F (easily reached during deep evacuation), vapor pressure drops to just 96 microns.¹