The efficiency rating on a new air conditioner or heat pump is what a matched system achieved in a test cell. What you actually get in your basement and backyard depends on how it was put in. A 2021 review of residential HVAC fault research reported that installation and operating faults add about 20.7 TWh of energy consumption across U.S. residential HVAC systems each year ([Ejenakevwe & Song, 2021](https://asmedigitalcollection.asme.org/IMECE/proceedings/IMECE2021/85642/V08BT08A045/1132971)). Commissioning — the set of field tests that verify an install before the truck leaves — is how you keep that gap small.
The deep-vacuum (micron) test
Before refrigerant goes into a new line set, the lines and indoor coil have to be evacuated to remove air and moisture. The instrument is a digital micron gauge, and ACCA describes the common industry target as 500 microns or less, verified with a decay (or hold) test — isolate the system from the pump and confirm the vacuum holds rather than creeping back up ([ACCA](https://hvac-blog.acca.org/matt-how-can-using-a-micron-gauge-improve-the-accuracy-of-system-evacuation-and-vacuum-processes/)).
Why it matters: moisture left in the system reacts with refrigerant and compressor oil to form acids that shorten compressor life, and trapped air (non-condensables) raises head pressure and cuts capacity. Separately, the EPA's Section 608 program governs refrigerant recovery and the handling requirements before a system is opened or charged — that's a regulatory framework, distinct from the manufacturer's installation vacuum target ([EPA](https://www.epa.gov/section608)).
A micron gauge at the pump is a lie.The pump will read a great vacuum at its own inlet while the far end of the line set is still full of air. Place the gauge at the system, then run the decay test — the reading that holds after you isolate the pump is the only one that counts.
Airflow and external static pressure
Rated efficiency assumes rated airflow. Technicians measure total external static pressure (TESP) across the indoor unit with a manometer. The federal/ENERGY STAR test reference for conventional ducted systems uses an external static pressure of 0.50 in. of water column (w.c.) ([ENERGY STAR](https://www.energystar.gov/sites/default/files/ENERGY%20STAR%20Version%206.1%20Central%20Air%20Conditioner%20and%20Heat%20Pump%20Final%20Specification%20(Rev.%20January%20%202022).pdf)) — but in the field, the right comparison is to that specific system's manufacturer blower table and rated maximum, not a universal pass/fail number.
High TESP points at a restricted coil, dirty filter, or undersized ductwork; low TESP can mean duct leakage or a blower set too slow. Either way the airflow drops, and peer-reviewed field work has shown air-side methods can detect airflow faults that quietly erode capacity ([Rogers et al., 2020](https://www.tandfonline.com/doi/full/10.1080/23744731.2019.1676093)). You can't verify refrigerant charge until airflow is right, which is why this test comes first.
Refrigerant charge verification
Once airflow is confirmed, the technician checks refrigerant charge by the manufacturer's prescribed method — superheat for fixed-orifice systems, subcooling for thermostatic-expansion-valve (TXV) systems — using a manifold set and temperature clamps. The actual target numbers are OEM-specific, printed on the unit or in its service literature, not a rule of thumb. ACCA frames commissioning as verifying airflow and refrigerant charge together (along with controls and connectivity on communicating systems) — a system that clears one test but not the others isn't commissioned ([ACCA](https://hvac-blog.acca.org/ahri-1380-compliance-opportunities-and-best-practices-for-contractors/)).
| Test | What it catches | Instrument | Target / method |
|---|---|---|---|
| Deep vacuum (micron) | Moisture, non-condensables, leaks | Digital micron gauge | ACCA industry target ≤500 microns + decay/hold test |
| External static pressure | Restricted coil, dirty filter, undersized duct | Manometer | Compare TESP to manufacturer blower table / rated max |
| Refrigerant charge | Under- or overcharge | Manifold + temp clamps | Manufacturer's method (superheat / subcooling) — after airflow verified |
| Recovery & handling | Refrigerant venting | Recovery machine, low-loss fittings | EPA Section 608 requirements |
"We fired it up and it's blowing cold" is not commissioning.Cold supply air tells you the compressor runs. It does not tell you the vacuum was deep, the airflow is at spec, or the charge is correct. Ask for a commissioning report with the actual readings — and the decay test result.
Why this matters more in the A2L era
The 2025 transition to A2L refrigerants (like R-32 and R-454B) doesn't change the 500-micron vacuum target, but it does change the recovery equipment and handling discipline required to get there safely — which is all the more reason the evacuation step can't be skipped or rushed. (We cover the refrigerant transition in detail here.)
The bottom line
A rating is a ceiling, not a promise. Commissioning is the set of measurements — vacuum depth, airflow and static pressure, refrigerant charge — that turns a hooked-up unit into a verified system. The few extra hours on install day are what separate the efficiency on the brochure from the efficiency on your utility bill.
HVAC Zone Inc is a multi-brand dealer; this article is brand-neutral and names no product as "best." This content is educational and not a substitute for a site-specific assessment by a licensed professional. Want an install with documented commissioning readings — vacuum decay, static pressure, and charge verification? Request a consultation and we'll show you the numbers, not just the cold air.