No regulation sets a vacuum level to be reached on a refrigerant circuit. The figure that binds you is the one in the installation manual of the unit you are commissioning, and that is the figure to record, not a number learned on a course. What is regulated is the work itself: any handling of fluorinated refrigerant requires a company certificate and a personnel qualification under the Fluorinated Greenhouse Gases Regulations 2015, and once commissioned the equipment enters the leak checking regime of the retained Regulation (EU) No 517/2014, from 5 tonnes CO₂ equivalent of charge upwards. The evacuation itself is only ever proved by a dated reading in the commissioning file.
Why vacuum evacuation is essential on a heat pump
Protecting the compressor and avoiding moisture-related faults
Vacuum evacuation drives out air and, above all, water from the refrigerant circuit. On a heat pump, moisture can react with the oil and the refrigerant, form acidic compounds and accelerate corrosion. The result: premature compressor wear, fouling, and the risk of frost forming in the expansion components.
Guaranteeing performance: pressure, temperature, efficiency and consumption
An insufficient vacuum leaves non-condensable gases behind. They push pressures up, throw off condensing and evaporating temperatures, and make the charge less reliable. The heat pump delivers less useful power, draws more current and consumes more. Vacuum evacuation stabilises real efficiency and control.
Reducing callbacks: typical symptoms of insufficient vacuum evacuation
Callbacks often show up as intermittent faults or erratic performance. The most common signs are:
- Abnormally high HP, safety trips.
- Localised frost at the expansion valve or on the liquid line.
- Compressor noise, overheating and hot-oil smells.
- Unstable discharge temperatures, discomfort and short cycles.
- Recurring fault messages after a restart.
Preparing the refrigerant circuit before vacuum evacuation
Preliminary checks: tightness, tightening, flares and service valves
Before starting the vacuum, check that everything is mechanically clean. Well-centred flares, clean seating surfaces, a thin film of refrigeration oil if the manufacturer specifies it, then tightening to the correct torque. Run a dry nitrogen tightness test and also check the service valve caps, often forgotten on a heat pump.
Recommended equipment: vacuum pump, vacuum gauge, hoses and valve cores
A 2-stage vacuum pump with fresh oil saves time. Add a micron vacuum gauge, fitted as close as possible to the installation, not just on the manifold. Use short, large-bore hoses, and a valve core removal tool to speed up evacuation.
Best practices on site: hose management and cleanliness to limit air and water ingress
Every second in open air brings in moisture. Keep hose ends capped, avoid unnecessary fittings and purge the hoses before opening the circuit. Work with clean, dust-free rags. A well-sealed installation reaches vacuum faster and holds it better.
Vacuum evacuation method: clear steps for heat pump commissioning
Connection and sequence: setting up the vacuum gauge and valves
On a split heat pump, connect the vacuum pump to the service ports with short, large-diameter hoses. Place the vacuum gauge on the installation side, ideally on a dedicated port, to measure the actual vacuum and not the manifold's. Keep the service valves closed. If possible, remove the valve cores during the operation to reduce pressure drop.
Reaching the target vacuum: duration, stability and adjustment based on line length
Start the pump, open the manifold valves and let the vacuum drop to the manual's threshold, quoted by manufacturers in absolute mbar, in kPa or in microns depending on the brand. Copy that figure onto your commissioning sheet before you start: it is the one that will be held against you, not a rule of thumb. Duration varies with moisture, diameter and line length, and shortens with short hoses, a suitable pump flow rate and a measurement as close as possible to the indoor unit.
Vacuum decay test: interpreting pressure rise before opening the refrigerant valves
Isolate the installation, close the manifold valves then stop the pump. Monitor the rise for 10 to 15 minutes. A slow rise can indicate residual moisture. A fast rise suggests a leak. As long as the hold isn't correct, don't open the service valves to release the refrigerant.
Common heat pump mistakes and quick fixes to apply
Forgetting the vacuum gauge: why the manifold gauge isn't enough
On a heat pump, the manifold's pressure gauge shows a pressure, but not the quality of the vacuum. To verify evacuation, you need a micron vacuum gauge, fitted as close as possible to the unit, ideally after removing the valve cores. The goal is to confirm a true vacuum evacuation and avoid residual water.
Leak, outgassing, moisture: diagnosing an abnormal vacuum rise
After isolation, monitor the rise:
- Fast, continuous rise. Suspect a leak. Run a nitrogen test, then locate and repair the fittings.
- Slow rise that stabilises. Often moisture. Restart the vacuum, with a nitrogen sweep and hold time.
- Rise in steps. Possible outgassing from the hoses, seals or oil.
Worn pump and used oil: how to restore effective vacuum evacuation
If the vacuum plateaus, start with maintenance. Drain and replace with fresh oil, check the check valve, seals and level. Shorten the hoses, switch to a larger diameter, and isolate unnecessary accessories. A clean pump pulls better than a bigger one.
Traceability and requirements in 2026: securing your commissioning
Nobody audits the vacuum after the event. What is audited is the leak checking regime the equipment enters the day it is commissioned, and that is the date to put on the handover sheet.
| Charge of the equipment | Leak check | With a leak detection system |
|---|---|---|
| From 5 tonnes CO₂ equivalent | every 12 months | every 24 months |
| From 50 tonnes CO₂ equivalent | every 6 months | every 12 months |
| From 500 tonnes CO₂ equivalent | every 3 months | every 6 months |
Intervals set by Article 4 of the retained Regulation (EU) No 517/2014. The threshold is counted in tonnes CO₂ equivalent, so at equal charge an R410A and an R32 system do not land in the same band, and an R290 system falls outside the fluorinated gas regime altogether.
Commissioning file: vacuum evacuation readings, hold test and site photos
For a heat pump, keep a simple file that proves the quality of the commissioning. Note the vacuum evacuation (value reached, duration, hold), the nitrogen hold test and the final charge, then carry that charge into the equipment's F Gas record, with the tonnes CO₂ equivalent calculation that decides whether a leak checking interval applies at all. Add 4 to 6 dated photos. Indoor unit, outdoor unit, refrigerant lines, condensate drainage, labelling.
Good practice to limit disputes: explaining to the client and signing off on handover
Explain to the client what was checked and what's normal. For example, a noise during defrost or shorter cycles depending on the weather. Have a handover signed, with reservations if needed, and hand over the manuals. This often means fewer discussions later.
Team organisation: standardising the vacuum evacuation procedure across all your jobs
To avoid discrepancies between teams, standardise a single form and a set order of operations. Vacuum evacuation, tightness check, parameter setup, then final readings. Train everyone on the same tools and require filing in a single job file. That file is driven from the client record, photos and snag clearing included.
