A refrigerant leak in a VRF system is the refrigerant slowly escaping from a point in the copper pipe, a weld, a flare fitting or inside a unit. Because a single building has hundreds of meters of pipe and dozens of connection points, finding the leak's location is one of the most time-consuming jobs of VRF service. With the right method and sequence, the leak can usually be found.
How can you tell there is a refrigerant leak?
The most common symptom of a refrigerant leak is the system's capacity slowly dropping. Indoor units no longer cool or heat as before, and the outdoor unit runs for longer. As the leak progresses, low pressure, high discharge temperature or low refrigerant error codes start to appear.
- The farthest or top-floor indoor units losing performance first.
- Icing of the indoor unit coil or the pipe connections in cooling mode.
- Oily stains on pipe connections, flare fittings or under the unit.
- A low pressure or low refrigerant warning on the outdoor unit.
Some of these symptoms can also come from a dirty filter, a faulty expansion valve or a sensor problem. That is why measurements should be taken before saying "the refrigerant is low, let's top it up".
Why does leak searching come before refrigerant charging?
Charging refrigerant without finding the leak only postpones the problem by a few weeks or a few months; money and refrigerant keep escaping. In addition, in a VRF that runs for a long time with a low charge, the compressor is cooled insufficiently, oil return is disrupted and the risk of breakdown increases.
F-gas regulations are also based on this order: when a leak is detected it is repaired first, then the repair is checked to have held, and the work is recorded. For systems above a certain charge amount, periodic leak checks and a service record are mandatory. These operations should be carried out by certified personnel.
The cost side is not small either. In a large VRF system the refrigerant charge can reach tens of kilograms; a slow leak can use up a significant part of this amount over a year. The refrigerant lost at each charge is both a direct cost and a greenhouse gas emission.
What methods are used to search for a leak in a VRF?
Leak searching is a process that moves from a rough scan to pinpoint detection. In the field, several methods are usually used together.
01Preliminary diagnosis by pressure and temperature measurement
The technician measures suction and discharge pressures with a manifold, and superheat and subcooling with a thermometer. If the values confirm low refrigerant, the leak search begins. This step distinguishes whether the problem is really a lack of refrigerant.
02Electronic leak detector
Pipe connections, flare fittings, service valves, indoor unit coils and branch points are scanned one by one with a sensitive electronic detector. The detector senses small leaks too, but it can give misleading results in windy environments or rooms with strong ventilation.
03Foam test
Leak-detection foam is applied to the suspect point the detector indicated. Bubble formation shows the exact location of the leak. It is a simple but reliable verification method.
04Nitrogen pressure test and zoning
If the leak cannot be found during operation, the refrigerant in the system is recovered with suitable equipment and the circuit is brought to the test pressure the manufacturer specifies with dry nitrogen. In VRF systems using R410A, this value is generally in the 38–42 bar range; the exact value is taken from the manufacturer's manual. The pressure is monitored for a set time, usually 24 hours. If the pressure drops, the line is divided into zones with the help of valves to narrow down which branch the leak is in.
Tests done by adding a small amount of tracer gas to the nitrogen (for example a nitrogen-hydrogen mixture) make it easier to locate a leak on hard-to-reach lines. Adding dye or leak-stop additives to the refrigerant is generally not recommended in VRF systems; it should be considered only if the manufacturer approves.
Where do leaks occur most often?
Most of the VRF leaks we see in the field are concentrated at a few typical points. If the leak search starts from these points, the time is shortened considerably.
- Flare connections: Wrong torque, a poorly formed flare or vibration at indoor unit connections causes leaks.
- Brazed joints: In joints brazed without nitrogen flowing through, oxide forms; over time pores and leaks can appear.
- Branch (joint) points: They are overlooked because they stay inside the suspended ceiling.
- Service valves and charging ports: The cap seal or valve stem may leak.
- Indoor unit coils: Small holes can form as a result of corrosion or mechanical damage.
- Mechanical damage: Pipes that were drilled, crushed or hit by a screw during renovation.
If renovation, a suspended ceiling replacement or drywall work has been done in the building, the leak search should start from that area. A significant share of the leaks we find in the field appear after this kind of work.
Is your VRF system leaking refrigerant?
We locate and repair the leak on site, charge the system by weight and record the work.
What is done after the leak is found?
After the leak point is repaired, the circuit is put through a nitrogen pressure test again and it is verified that the pressure holds. Then the system is evacuated; the vacuum is monitored for a set time to make sure moisture and air are completely removed. Finally, refrigerant is charged by weight according to the manufacturer's calculation method.
The target in evacuation is generally around 500 microns or below the value the manufacturer specifies. If the value rises quickly after the pump is switched off, there is still moisture or a small leak in the circuit and charging is not started. In large VRF circuits, evacuation can take hours depending on pipe volume.
In VRF, the charge amount is calculated from pipe lengths and diameters; topping up refrigerant by looking at pressure does not give correct results in these systems. After charging, the system is run and the pressures, superheat and error history are checked, and the work is entered in the service record.
What can the user do, and what should they not do?
The most useful thing a user can do is notice the symptoms early and keep a record. Noting which units are losing performance, the error codes and the dates speeds up the diagnosis.
The refrigerant circuit, service valves and fittings must never be tampered with. Refrigerant can cause cold burns on contact with skin; in a small, enclosed room a heavy leak can reduce the oxygen in the air. Leak searching and refrigerant charging must always be done by a qualified and certified technician.
At YOİ Mühendislik we detect leaks in VRF systems using electronic detectors, nitrogen tests and zoning, and charge by weight after repair. For details, see our refrigerant leak and charging service; if your system is showing an error, you can read our VRF error codes article.
Frequently asked questions
Is it enough to just add refrigerant to a VRF?
No. Refrigerant added without finding and repairing the leak escapes again and the problem is only postponed. The leak must be located and repaired first, and then the system should be charged by weight.
How long does a leak search take in a VRF?
An accessible leak can be found in a few hours. For lines inside suspended ceilings or hard to reach, when a nitrogen test and zoning are needed, the time can stretch to one or several days.
Can the system run during leak detection?
Scanning with an electronic detector can be done while the system is running. During a nitrogen test the relevant refrigerant circuit stays off; if the building has other independent outdoor unit groups, they keep running.
Is a refrigerant leak dangerous in a VRF?
Commonly used refrigerants have low toxicity, but a heavy leak in a small, enclosed room can reduce oxygen. If you suspect a significant leak, ventilate the area and call a qualified service technician.
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