Have you been to multiple service or breakdown jobs at the same address & you can see the telltale signs their aircon needs replacing?

You’ve already fixed the air con a couple of times & it’s not as efficient as it used to be perhaps it’s time to discuss replacing the system for a new one?

The customer should already be aware of what the issues are so an obvious way to approach this is to clarify what’s already been previously said to them.

Point out things like;
– It’s not as cool as it use to be – point out you’ve focused on the same issue the last few visit’s & even with repairs it’s still not blowing as cool as it should be
– Ask to look at their last couple of electric bills – explain that you’d be curious to see if it’s as efficient as what is use to be & if a new system could save them some money on bills
– Moisture build up – this is an obvious one on why a customer should look at a replacement, but the unfortunate this is not all customers will understand why they should, moisture creates mould & bacteria, show them the depth of the moisture if you can

Those things aside, if their home has grown over the years, the existing aircon might not be the right fit anymore. If they’ve added some extensions to their home, you might need to suggest investing in a bigger, more efficient airconditioning unit.