Aircon refrigerant charge by weight: a number on record
Weighing the charge in against the manufacturer's figure ends the visit at a quantity somebody can write down and a stranger can retest. Every other approach ends at a judgement nobody present is able to repeat, including the person who made it.
By Team Snowflake | Updated 7 Aug 2026
The target is published before anybody reaches the flat
The quantity a system should hold was settled long before anyone was called out. A manufacturer fixed it for the model, printed it on the outdoor unit, and repeated it in the installation manual. Nobody standing in the flat wrote that number. Nobody standing in the flat can move it either.
Who authored the figure is what makes it usable as a reference. A target set by whoever is doing the work can be adjusted to suit the work. A target published years earlier, by a party holding no stake in the invoice, cannot be. The owner can look it up. So can the next technician, and so can anybody reading the paperwork during an argument.
The printed quantity covers the machine plus a reference length of pipework, so a flat that needed a longer route needs more refrigerant than the plate states. Manuals give a rate for exactly that. Daikin's R32 split manual for the RXF, RKF and RXC outdoor units calls for no addition below 10 metres of pipe, then 17 grams for every metre past it. Both of those belong to those models specifically. The reference length and the rate each shift from one manual to the next, so the pair has to come off the document for the unit actually 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 on the day by eyeing the size of the rooms. Whether the route was permitted at all is a separate matter, governed by pipe run length rather than by the amount of gas.
| Where the figure came from | Can anyone else arrive at it | What the file inherits |
|---|---|---|
| Where the figure came fromThe quantity printed on the outdoor unit | Can anyone else arrive at itYes, from the model number and a public manual | What the file inheritsA target that outlives everybody who was there |
| Where the figure came fromThe manual's rate applied to a measured route | Can anyone else arrive at itYes, given the routed length and that rate | What the file inheritsAn adjusted target with its arithmetic attached |
| Where the figure came fromA judgement about how big the rooms looked | Can anyone else arrive at itNo, the reasoning left with the person who made it | What the file inheritsA number carrying no source |
| Where the figure came fromA gauge matched to what seemed right that day | Can anyone else arrive at itNo, the day cannot be set up a second time | What the file inheritsA note about conditions, not about contents |
When the plate cannot be read
Plates fade. Outdoor units sit on ledges in full sun and salt air, and a figure printed on a sticker does not always survive that treatment. Paint from a block repaint covers plenty of the others.
The quantity survives anyway, because the plate is a copy rather than the original. A model number is recoverable from the indoor unit, the handover paperwork or the warranty card, and manufacturers publish their manuals openly. An unreadable plate slows the lookup down. It does not convert the quantity into a matter of opinion.
Why is a weight checkable when a pressure reading is not?
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 during a heatwave. Anybody who opens that file understands precisely what the line claims, and understands precisely what would contradict it.
Put a pressure on the same invoice and the number arrives stripped of what gave it meaning. Outdoor temperature, indoor heat load, the setpoint, how long the compressor had already been going, what the fan was doing: all of it shaped the reading, and almost none of it gets written beside it. The figure survives. What made it interpretable does not.
None of that makes gauges pointless. Superheat and subcooling exist to turn readings into a judgement about how the circuit is being fed, and that judgement is worth having. What readings cannot do is leave a durable statement behind them. They characterise a machine while somebody stands in front of it, and stop characterising anything the moment that person drives away.
What the next technician can do with each line
Handed a quantity, a technician who doubts it has a route to settling the doubt. Refrigerant taken out of the circuit goes on a scale, and the two figures either agree or they do not. Disagreement then means something definite: gas has left the system, or the original line was wrong.
Handed a pressure note, that same technician has nowhere to go. The day cannot be reproduced, so the reading cannot be tested, so there is nothing to agree or disagree with. Not being contradictable sounds like a strength. It is the reverse. A claim that cannot fail any test is carrying no information about the equipment.
Where weighing the charge in is not available
Weighing in wants an empty circuit, and emptying a circuit is not always proportionate to the fault sitting in front of it. That is the honest limit on the method, and it 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 to the room that is complaining. Draining all of it to settle a question about one bedroom is a heavy piece of 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 has been refilled, dried and proven again. Where that pause is not on offer, the visit works from readings and the quantity question waits for a window when it is.
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. It has simply stopped being the target for that machine, and 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 rather than estimation. That situation sits inside top-up vs recharge, where the deciding factor is whether the starting amount was ever established.
What replaces the method matters as much as the limit does. 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. It is a weaker one for the file, because it reports conditions rather than contents.
| Why weighing in is off the table | What the visit works from instead | What the paperwork should say |
|---|---|---|
| Why weighing in is off the tableOne circuit feeds several indoor units and one room is complaining | What the visit works from insteadReadings gathered while the system runs | What the paperwork should sayThat the amount was assessed, not established, and why |
| Why weighing in is off the tableThe aircon cannot stop long enough to be emptied and refilled | What the visit works from insteadReadings, plus a note of what got deferred | What the paperwork should sayThat the quantity question is open, and what would close it |
| Why weighing in is off the tableAn indoor unit or the pipe route has changed since handover | What the visit works from insteadA target rebuilt from the route as it stands now | What the paperwork should sayThe rebuilt target and the inputs behind it |
| Why weighing in is off the tableA repair captured and weighed the refrigerant coming out | What the visit works from insteadThat captured figure, returned to the circuit | What the paperwork should sayWhat came out, what went back, and the model's target |
Assessed and established are different words
Two verbs do separate work here and get swapped around freely. An amount that has been assessed was judged against how the equipment is behaving. An amount that has been established went across a scale. The first is an opinion with evidence under it. The second is a measurement.
Neither is dishonest and both earn their place. Trouble starts in a file where the two are indistinguishable. Somebody reading it long afterwards cannot tell whether the figure came off a scale or out of a judgement about a running machine. One extra word on the invoice removes that ambiguity permanently.
What a charge record has to contain
A charge record is short. It occupies one line of an invoice and answers one question: what does this circuit hold now, and against which target. Most gas invoices in circulation answer neither half of it.
Six items cover it, and each one 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. The scale reading is the single item nobody outside the room can reconstruct, which is exactly why it belongs on paper rather than in somebody's memory.
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 artifact: one visit, one quantity, one target. Plenty of systems carry neither, and the charge line is the cheaper of the two to start keeping.
- 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
Lines that look like a record and are not
Three phrases do a passable impression of a record. Gas topped up reports that an amount moved while declining to say which amount. Pressures checked and found normal describes an afternoon. Charged to specification asserts the conclusion while withholding the figure that would let anybody test it, which makes it the most misleading of the three, because it sounds the most rigorous.
One question fixes that, and it is not a confrontational one. Ask what figure the specification actually is, then ask for that figure on the paperwork. A visit that worked to a target knows the target and has no reason to hold it back. A visit that did not will offer reassurance in place of a number, and the swap is easy to hear.
Asking so the answer comes back as a quantity
The aim is not to interrogate anybody. It is to shape the question so the reply has to contain a number, because a question that can be answered 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 from a visit that will not, and neither reply changes what happens next. 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?
A figure that is not available yet is a fair answer
Deferral and deflection sound alike for about a second. Somebody quoting before seeing the unit may genuinely not have the number to hand, and saying so is not evasion. The reply that counts names what has to happen for the number to exist: the model read off the plate, the manual pulled, the route measured.
Deflection skips all of that. It moves to reassurance, to how long the person has been in the trade, or to an observation that the system will be fine. None of those is a plan for producing a figure, and the absence of a plan is itself the answer.
If the work is already finished
An owner asking these questions after the van has gone is not too late for all of them. The target remains recoverable, because the model and the manual have not changed. What cannot be recovered is what went into the circuit that day, and no amount of paperwork will produce it retrospectively.
That asymmetry is worth carrying forward rather than backward. The target can be worked out at any point and kept on file. The contents stay unknown until something empties the circuit, so the useful move is making sure that when it happens, the figure gets written down instead of leaving with whoever took the reading.
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