Correct vacuum testing during AC installation
Why vacuum testing is mandatory and what skipping it leads to — with real-world examples.
Vacuum testing is one of the most decisive steps of an AC installation — yet many installers either run it as a formality or skip it. The result: a unit that starts manifesting "weird" problems within 1–2 years — compressor noise, rising power use, lukewarm air on cooling mode, frequent freeze-ups.
What happens without vacuum testing
The refrigerant line ships from the factory under vacuum. No moist air inside. But the moment you open the line for installation — air enters. Air = water vapour = corrosion. Water vapour + refrigerant = acid that eats compressor internals over time.
Vacuuming after installation is the only way to fully evacuate that air and moisture. The process takes 30–45 minutes and requires a vacuum pump that can pull at least −500 microns.
Signs of correct vacuum
We pull until the gauge reads −500 microns and that value holds for at least 10 minutes after we stop the pump. If pressure rises again — there is a leak in the system, and we start hunting for it.
Our team logs the vacuum reading as a photo — part of the photo report the client receives at the end of installation.
Consequences of skipping
First 6–12 months — unit works fine. Next 1–3 years — cooling capacity drops, power use rises 10–20%. After 3 years — compressor starts to whine, freeze-ups become regular, finally compressor replacement (60–70% the cost of a new unit).
This is the scenario we often run into during warranty repairs. In many cases the root cause is a vacuum step skipped 2–3 years prior.