Aircon Refrigerant Charge by Weight: A Number on Record

The quantity a system should hold was settled long before anyone was called out. A manufacturer fixed it, printed it on the outdoor unit, and repeated it in the manual. Nobody standing in the flat wrote that number, and nobody standing in the flat can move it.

Who authored the figure is what makes it usable as a reference. A target set by whoever does the work can be adjusted to suit it; a target published years earlier, by a party with no stake in the invoice, cannot. The owner can look it up.

The printed quantity covers the machine plus a reference pipe length. A flat needing a longer route needs more refrigerant than the plate states, and manuals give a rate for it. Daikin's R32 split manual for the RXF, RKF and RXC outdoor units calls for no addition below 10 metres, then 17 grams for every metre past it. Both figures belong to those models; the rate shifts between manuals, so check the document for the unit on the wall.

An adjusted target is still a published one. The route was measured, the rate came off a page, and the sum runs again in the hands of a second person who never attended. That is not true of a quantity someone arrived at by eyeing the size of the rooms. Route permission is a separate matter, governed by pipe run length.

A weight describes the machine. A pressure reading describes an afternoon. That distinction decides which of the two can still be read years later, and it has nothing to do with which measurement takes more skill.

Put a quantity on an invoice and it needs no supporting information to keep its meaning. Grams read the same during a cool spell and a heatwave. Anybody who opens that file understands what the line claims, and what would contradict it.

Put a pressure on the same invoice and the number arrives stripped of what gave it meaning. Outdoor temperature, indoor load, the setpoint, compressor run time, fan speed: all of it shaped the reading, and almost none gets written beside it. The figure survives; what made it interpretable does not.

None of that makes gauges pointless. Superheat and subcooling turn readings into a judgement about how the circuit is being fed. What readings cannot do is leave a durable statement behind them: they characterise a machine while somebody stands before it.

Weighing in wants an empty circuit, and emptying one is not always proportionate to the fault. That limit is worth knowing before asking for it.

Large multi-split and VRF systems are the clearest case. One circuit serves many indoor units, so the quantity belongs to the whole installation rather than the room that is complaining. Draining all of it to settle a question about one bedroom is heavy work aimed at a light problem.

Systems that cannot be taken out of service are the second case. Emptying a circuit stops the aircon until it is refilled, dried and proven again. Where that pause is not on offer, the visit works from readings and the question waits.

The third case is a circuit that has drifted away from the document describing it. An indoor unit swapped for a different capacity, or pipework re-run during a move with nothing noted about the new route, leaves an installation the manual no longer fits. The published figure still exists, but it has stopped being that machine's target; rebuilding the target comes first.

There is also a case where the method is available and unnecessary. A repair that captured what came out has already produced the number, so putting the same amount back is arithmetic, not estimation. That situation sits inside top-up vs recharge.

What replaces the method matters as much as the limit. Where the circuit stays sealed, superheat and subcooling become the available evidence, and they answer a narrower question: not how much sits in there, but whether what sits in there is feeding the coil correctly. That is a real answer but a weaker record: it reports conditions, not contents.

A charge record is short. It occupies one line of an invoice and answers one question: what does this circuit hold, and against which target. Most gas invoices answer neither half.

Six items cover it, and each is there so a stranger can rebuild the claim without having attended. The model number leads to the published quantity. The routed length and the manual's rate reproduce the adjustment, and the scale reading is the one item nobody outside the room can reconstruct.

The installation-day version of this is broader and belongs to commissioning readings, which cover everything that should have been noted when the system was new. A charge line on a service invoice is the narrower artefact: one visit, one quantity, one target.

• •The outdoor unit model number, since the published quantity attaches to the model and to nothing broader
• •The refrigerant type, because the correct amount of the wrong type is still wrong
• •The target: the printed figure plus whatever the route adds, with the routed length stated
• •What the scale read going in, and on a job that emptied the circuit first, what the scale read coming out
• •Whether that amount was established across a scale or assessed from readings
• •The date, because a quantity is a claim about a moment and the following claim gets compared to it

The aim is not to interrogate anybody, only to shape the question so the reply must contain a number: a question answerable with a nod will be.

Yes-or-no phrasing collapses on contact. Will you weigh it in draws a yes from a visit that will and one that will not, and neither reply changes anything. How much is going in cannot be answered that way: either a figure arrives or a visible gap does, and the gap tells you as much as the figure would.

• •What figure is the scale being set to, and which document is it from?
• •How long is the routed pipe here, and what does the manual add for that length?
• •Did that amount go across a scale, or was it judged from readings on a running system?
• •Which of those two words will appear on the invoice?
• •What on today's paperwork would a second opinion be able to test?