HVAC Commissioning and Handover: Refrigerant Charge Verification, Airflow Balancing and F-Gas Documentation

Summary

Commissioning is not a final box-ticking exercise — it is the process that validates that every element of the installation is working as designed and that the system will perform reliably over its service life. An uncommissioned or poorly commissioned system will run, but it will run inefficiently, use excess electricity, and often fail prematurely. The most common causes of early AC failure are incorrect refrigerant charge (over- or undercharge), inadequate vacuum (residual moisture in the circuit), and blocked or imbalanced airflow.

F-Gas documentation is a legal requirement, not optional. Under the UK F-Gas Regulation (retained from EU 517/2014 after Brexit), any person handling refrigerants must hold the appropriate F-Gas qualification, and any system containing fluorinated refrigerants must be accompanied by documentation of the gas charge, any additions or recoveries, and the identity of the certified engineer who performed the work. Failure to maintain documentation is a criminal offence under the UK F-Gas Regulation 2015 enforcement provisions, enforced by the Environment Agency and the Health and Safety Executive.

The handover pack is the final step. Many installers skip or rush the handover, and the consequences arrive six months later: the customer does not know how to change the filter, the warranty registration was never completed, and there is no record of the initial charge for future service engineers. A well-structured handover protects both the customer and the installer.

Key Facts

• Pre-commissioning: electrical supply — verify supply voltage (should be 230V ±10% for single-phase; measure under load), MCB rating and type (Type C), local isolator present and labelled, RCD protection confirmed
• Pre-commissioning: refrigerant circuit — pressure test with dry nitrogen at manufacturer-specified test pressure (typically 40–42 bar for R410A; check data sheet for R32 and other refrigerants), hold for minimum 1 hour, confirm no pressure drop
• Evacuation (dehydration) — use two-stage vacuum pump; pull vacuum to below 500 microns (66.7 Pa) on the vacuum gauge; hold vacuum with pump isolated for minimum 30 minutes — any rise indicates residual moisture or a leak
• Vacuum gauge — a manifold set pressure gauge is not accurate enough for evacuation; use a dedicated digital micron gauge (Torr or Pa range)
• Factory charge — the outdoor unit is factory-charged with refrigerant sufficient for the standard pipe length (typically 5–7 metres); additional refrigerant is required for longer pipe runs
• Additional charge calculation — manufacturer publishes an additional charge table (e.g., 20g/metre of liquid line above the standard length); weigh in using calibrated scales
• Weighing scales accuracy — electronic refrigerant scales must be accurate to ±10g minimum; ±5g preferred for small systems where total charge is under 1 kg
• Total system charge record — record the factory charge (from the outdoor unit data plate) plus any field-added charge; total is the figure used for F-Gas documentation
• Temperature differential (cooling mode) — supply air temperature minus return air temperature should be 8–12°C; less than 8°C suggests low charge or airflow issue; more than 12°C may indicate restricted airflow
• Temperature differential (heating mode) — with ASHP-mode operation, supply air is typically 15–20°C warmer than return; lower differential may indicate low charge or defrost cycle interference
• Airflow balancing — use an anemometer to measure velocity at grilles/diffusers; compare to design airflow; adjust louvres or dampers until all outlets are within ±10% of design
• F-Gas system label — must be permanently attached to the unit; must show refrigerant type, total charge weight in kg, GWP of the refrigerant, and CO2 equivalent (kg CO2e = charge kg × GWP)
• F-Gas service record — a written log of every refrigerant handling event (installation, top-up, recovery); must be retained for 5 years; must identify the F-Gas certified engineer for each entry
• Warranty registration — most manufacturers require online registration within 30–60 days of installation for extended warranty to apply; this is the customer's responsibility but the installer should prompt it
• Filter cleaning schedule — most split AC units require filter cleaning every 2–4 weeks in normal domestic use; dirty filters cause unit shutdown on high temperature or icing of the evaporator

Quick Reference Table

Detailed Guidance

Pre-Commissioning Checks

Before any refrigerant is released into the system, all pre-commissioning checks must be complete. This is the phase most often rushed — the customer is waiting, the job has overrun, and the pressure is to power up and demonstrate cooling. Rushing pre-commissioning is the fastest route to a warranty callout.

Mechanical checks: all pipe connections torqued to manufacturer specification (flare connections have specific torque values — do not over-torque, which distorts the flare and causes leaks); pipe insulation complete and continuous with no exposed sections (thermal bridging on suction pipe causes condensation and efficiency loss); indoor unit mounting brackets level and secure; outdoor unit mounting level (within 2 degrees) on anti-vibration feet; condensate pipe correctly graded and discharging to drain.

Electrical checks: supply voltage at the outdoor unit terminal block measured and recorded; correct cable termination (ring terminals or box-type terminals as required by unit — no bare stranded wire pushed into terminal blocks); earth continuity confirmed at both indoor and outdoor units; RCD tested (press the test button and verify it trips, then reset); local isolator present and labelled; cable routes clear of refrigerant pipe (refrigerant pipe surface temperatures can reach 80°C on the discharge line — cables must not be in contact).

Pressure test: connect a manifold set or dedicated test manifold to the system's service ports. Charge with dry nitrogen (not oxygen — never use oxygen near refrigerant equipment; risk of explosion) to the manufacturer's test pressure. For R410A systems, this is typically 40 bar on the high side; for R32, check the data sheet (R32 operates at similar pressures to R410A). Hold for a minimum of one hour with no pressure drop. Record the test pressure and duration on the commissioning sheet.

Evacuation to 500 Microns

Vacuum dehydration is the most technically critical pre-commissioning step. Its purpose is twofold: to remove non-condensable gases (primarily nitrogen from the pressure test and air from any pipe openings) and to remove moisture from the internal surfaces of the pipework. Moisture in a refrigerant system combines with refrigerant oil to form acids that attack the compressor bearings — the most expensive component in the system.

A two-stage vacuum pump is required. Single-stage pumps cannot achieve the required vacuum depth reliably. Connect the pump to both the high-side and low-side service ports via the manifold — evacuating from both sides ensures vapour paths reach all parts of the circuit.

The target is below 500 microns (66.7 Pa). Many engineers use a digital micron gauge connected to the manifold centre port. Pull vacuum until the gauge reads below 500 microns. Then isolate the pump (close the pump isolation valve on the manifold — do not turn off the pump while the valve is open or oil can be drawn into the system) and observe the vacuum for 30 minutes. If it holds stable, the system is dry and leak-free. If it rises toward atmospheric pressure, there is a leak. If it rises slowly and stabilises below 1,000 microns, there may be residual moisture — continue evacuation with heat applied to the pipe circuit if possible, or replace any suspect pipe sections.

Never use a manifold set's pressure gauge for vacuum measurement. Bourdon tube pressure gauges are not accurate below 100 mbar (100,000 microns) — they will show "vacuum" when the system is still at thousands of microns, giving a false pass. Always use a dedicated digital micron gauge.

Refrigerant Charge Verification

Split AC systems are factory-charged for a standard pipe length (typically 5–7 metres for domestic units). The outdoor unit data plate shows the factory charge weight and the maximum and minimum pipe lengths. When the installed pipe length exceeds the factory-charged length, additional refrigerant must be added.

The calculation is straightforward: additional charge = (installed pipe length − factory pipe length) × additional charge rate. The additional charge rate is published in the installation manual, typically in g/m of liquid line. For example, if the factory charge covers 7 metres and the installed liquid line is 15 metres, the additional charge is 8 metres × 20 g/m = 160g.

Refrigerant is added using a refrigerant cylinder on calibrated electronic scales. The scales must be accurate to ±10g minimum — for a small system with a total charge of 800g, a 10g error is 1.25%, which matters for system performance. For larger systems, ±5g scales are better practice.

Connect the refrigerant cylinder to the manifold centre port, purge the hose of air (briefly open the cylinder valve with the manifold valve closed, then crack open the manifold valve and allow a small amount of refrigerant to flush the hose before connecting to the service port). Weigh the cylinder before charging. Charge in liquid phase into the high side (unit off) for the factory charge, or as vapour into the low side with the unit running for top-up additions. Record the cylinder weight before and after; the difference is the charge added.

Under no circumstances estimate the charge by "feel," suction pressure, or manufacturer pressure charts alone. Pressure-based charging methods can give reasonable results for experienced engineers in controlled conditions, but they are not a substitute for weight-based charge verification, and they do not provide the auditable record required by F-Gas documentation.

Airflow Balancing

For systems with fixed-speed fan coil units, airflow balancing means verifying that the actual airflow matches the design specification and that all supply grilles and return paths are clear. For variable-speed inverter units, it means confirming that the unit's minimum and maximum airflow settings are appropriate for the space.

Use a calibrated anemometer (vane type or thermal type) to measure the face velocity at each supply grille. Multiply by the grille free area (usually stated on the grille data sheet or measured) to get volumetric flow in l/s or m³/h. Compare to the design target. Adjust the grille louvre angle or, for ducted systems, the volume control damper (VCD) settings until all outlets are within ±10% of design.

Check that return air paths are clear. A common installation fault is running supply ducts to all zones but not providing adequate return air paths — the system then operates at positive pressure with air leaking through gaps in the building fabric rather than returning through designated paths. For ceiling-void return systems, confirm that the void is connected to the return air plenum and that internal partition walls do not block the return air path.

The temperature differential test confirms airflow and charge together. With the unit running in cooling mode at rated capacity (or as close as site conditions allow), measure the return air temperature at the indoor unit intake and the supply air temperature at the nearest supply grille. The difference should be 8–12°C. A differential below 8°C typically indicates low refrigerant charge (the evaporator is not cooling fully) or excessive airflow. A differential above 12°C indicates insufficient airflow (dirty filter, blocked return, damper too closed) or very high refrigerant charge.

F-Gas Documentation Requirements

UK F-Gas Regulation (the UK retained version of EU 517/2014, as amended by the Fluorinated Greenhouse Gases (Amendment) Regulations 2019 and subsequent updates) requires the following documentation for any system containing fluorinated refrigerant:

System label: permanently attached to the outdoor unit (or to the indoor unit where the outdoor unit is in an inaccessible location). Must show: refrigerant type (e.g., R32, R410A), total system charge weight in kg, GWP of the refrigerant, and CO2 equivalent (kg charge × GWP). Labels must be permanent — engraved, embossed, or on a durable metal or UV-resistant plastic plate. Paper stickers are not acceptable.

Equipment log (service record): a written or electronic record that travels with the equipment. Must record: installation date, initial charge weight, subsequent top-ups or recoveries, refrigerant type changes (if any), name and F-Gas certificate number of every engineer who handled the refrigerant. Must be retained for 5 years from the date of the most recent entry. The customer is the legal duty-holder for maintaining this record; the installer should provide the completed record at handover.

Leak testing obligations: systems containing ≥3 kg CO2e of fluorinated refrigerant must be leak-tested at specific intervals. For systems of 3–30 tonnes CO2e, annual leak testing is required; for 30–300 tonnes CO2e, six-monthly; above 300 tonnes CO2e, quarterly. Many small domestic split systems fall below 3 tonnes CO2e and have no mandatory leak testing interval — but the record must still be kept.

For most domestic R32 systems (charge ~0.75 kg, GWP 675, CO2e = 506 kg — below 3 tonnes CO2e threshold), mandatory periodic leak testing does not apply but good practice is to check for leaks at annual service.

Customer Handover

The handover is the last impression you leave with the customer and the document that protects you if there is a dispute later. At minimum, the handover pack should include:

• Completed equipment log (F-Gas service record) — legal requirement
• System label confirmed fitted — legal requirement
• User manual for indoor unit(s) and outdoor unit
• Instructions for: switching on/off, changing mode (cooling/heating/fan), setting temperature, setting timer, cleaning filters, identifying error codes
• Filter cleaning schedule (typically every 2–4 weeks in normal use)
• Warranty information and registration instructions (most manufacturers require online registration within 30–60 days)
• Your contact details for servicing
• Annual service recommendation — explain that annual service maintains efficiency, preserves warranty, and is required for F-Gas documentation

Walk the customer through the controls. Many customers have never used AC before and will operate the system incorrectly — leaving it running on minimum temperature continuously, for example — resulting in high energy bills and a complaint to you. Five minutes of explanation at handover prevents months of follow-up calls.

Frequently Asked Questions

What vacuum depth do I need to achieve before charging?

Below 500 microns (66.7 Pa) as read on a digital micron gauge. Some installers target 300 microns for additional assurance, particularly on longer pipe runs where residual moisture is more of a risk. The 500-micron target is the widely accepted industry standard. Do not use a standard manifold gauge for vacuum measurement — it is not accurate enough.

Can I charge by pressure rather than weight?

Pressure/temperature charging methods (using manufacturer saturation tables) can give a rough indication of charge status but are not a substitute for weighing. Ambient temperature, pipe length, operating conditions, and superheat/subcooling all affect the system pressure and introduce error. The F-Gas documentation requires the charge weight to be recorded — pressure-based charging cannot provide this with the necessary accuracy. Weigh the charge.

The customer wants to know if they can top up the refrigerant themselves.

No. Handling fluorinated refrigerants requires an F-Gas qualification (City & Guilds 2079 or equivalent for the specific equipment category). It is illegal for an uncertified person to handle F-Gas refrigerants — including purchase. The customer cannot buy refrigerant in the UK without proof of certification, and cannot legally add it to the system. Any top-up must be performed by a certified engineer with the appropriate equipment records.

How do I complete the F-Gas label if the system has multiple indoor units on one outdoor unit?

The label documents the total charge in the system as installed. For a multi-split system, the outdoor unit holds the factory charge plus any field-added charge for all pipe runs. Calculate the total: factory charge (from outdoor unit data plate) + all field-added charge (from your scales records during commissioning). This total goes on the label in kg, along with the refrigerant type, GWP, and CO2e equivalent.

What if I find the system slightly undercharged on a service visit — do I need to record it?

Yes. Any addition of refrigerant must be recorded in the equipment log with the date, amount added (in kg, to ±10g accuracy), total system charge after addition, your name, and your F-Gas certificate number. The log must be updated and retained. If you add refrigerant without identifying and repairing the leak, you are also in breach of F-Gas requirements — the regulation prohibits topping up a leaking system without repairing it first.

Regulations & Standards

• UK F-Gas Regulation (retained EU 517/2014, as amended by SI 2019/583 and subsequent amendments) — requirements for handling, documentation, labelling, and leak testing of fluorinated refrigerants

• F-Gas Regulation (EU) No 517/2014 — original EU regulation; relevant for historical context and interpretation

• City & Guilds 2079 — F-Gas qualification for handling fluorinated refrigerants in the UK; split into categories by equipment type (Category 1 for all equipment)

• REFCOM Register — the UK's voluntary register of companies competent to handle refrigerants; membership demonstrates F-Gas compliance

• BESA TR/19 — BESA guidance on internal cleanliness of ventilation and air conditioning systems; relevant to pre-commissioning cleanliness checks

• BS EN 378:2016 (Parts 1–4) — Refrigerating systems and heat pumps; safety and environmental requirements; covers pressure testing, commissioning, and decommissioning procedures

• CIBSE Commissioning Code R (Refrigerating Systems) — guidance on commissioning of refrigerant-based systems; references pressure testing, evacuation, and charging procedures [verify current edition]

• F-Gas Enforcement Regulations (UK) — Environment Agency and HSE powers; criminal penalties for non-compliance including unlimited fines

• UK F-Gas Regulation guidance — GOV.UK, Environment Agency / DEFRA

• REFCOM: F-Gas technical guidance and register — REFCOM

• BS EN 378:2016 — Refrigerating Systems and Heat Pumps — BSI Group

• CIBSE: Commissioning Codes — CIBSE

• City & Guilds 2079: F-Gas qualification — City & Guilds

• f gas regulations guide — Full F-Gas regulation guide: qualifications, record-keeping, and refrigerant phase-down

• refrigerant types comparison — R32, R410A, R454B, R290 compared: GWP, pressure, safety classification

• ac electrical supply requirements — Electrical pre-commissioning checks: circuit, isolator, RCD

• ac condensate drainage — Condensate drainage commissioning: drain test and pump check

• ac maintenance annual service — Annual service checklist referencing commissioning data

• split system installation — Full installation sequence; commissioning follows installation