Why topping up a leaking system isn't legal here

What does the code actually say?

Clause 9.5.3 is the one to know. Where a leak is detected, all refrigerant must be removed from the system or affected section, and the leak repaired. Where a leak is suspected but not detected, all refrigerant must be removed, and the system or affected section must be leak tightness tested.

Then clause 4.9.8 closes the obvious workaround. Repairs must be carried out and verified before the system is charged with refrigerant. Repairs must not be made with the system pressurised. And clauses 4.10 and 6.1 require evacuation before charging.

Put those clauses together and there's no legal way to add gas to a system that's losing it. In Australia, "gas it up and see" is non-compliant on any refrigerant, blend or pure.

Is there a technical reason too?

On a blend there's a second argument that stands on its own. Clause 12.3.1 says the recycling process is more complicated for blended refrigerants, because preferential leakage or separation within the system may have resulted in a change of blend composition.

In plain terms, a blend can leak one of its gases faster than the others. So what's left in a leaking system may not be the original mix any more. Top it up with fresh product and you've got a mixture that matches nothing on the label, which throws out capacity, pressures and glide (the temperature shift as a blend boils).

That's true of R410A, R454B and R407C. It isn't true of R32, which is a pure refrigerant. But the legal rule covers blends and pure gases alike, so R32 being pure doesn't get you out of it.

How do you explain it to the customer?

This is the awkward part. A customer with a slow leak wants the cheap option, and the cheap option isn't available to you. Have the explanation ready rather than making it up on the driveway.

1. Name the obligation, not your preferenceIt isn't that you'd rather do the bigger job. It's the code you work under. That's an easier conversation and it's the true one.
2. Explain what a top-up actually buys themThe same leak, a second call-out, and refrigerant vented to atmosphere in between.
3. Give them the real optionsFind and repair, or replace. Both are real answers. Topping up isn't one.