Repaired and working again.
Found a YouTube of a refill of my particular ElectriQ unit. Didn't agree with everything he did but it was helpful:
I bought a canister of nitrogen to pressure test.
The canister has a 10mm connection. Finding a tap with 10mm to 1/4" SAE flare connections proved impossible. Most seem to be 11mm, listings of 10mm taps had no details of the output connections, and nobody would reply to requests for details.
In the end I screwed a 1/4" SAE flare connection into a CO2 gas regulator I had that happened to have a 10mm input.
The pressure test using a can of Leak Detector revealed a leak on one of the connections directly onto the outside unit. A slight tightening with spanner stopped the leak and the aircon held pressure overnight :->
The 1/4" Male to 5/16" adapter for the aircon charging port that I had used when first installing started leaking at the 1/4" end. This was the type with a slightly bent section of thin steel tube between the two connectors. I bought a replacement that was a short solid brass item with the connectors at each end, no pipe, no leaks.
I bought a 370g canister of R290, and a tap with 1/4" SAE flare output. Didn't get anywhere near 370g of R290 out of it, according to the kitchen scales. So I warmed the canister up by immersing it in a jug of hot water when it was nearing empty, to increase the gas pressure .
Don't do that to a canister that isn't connected to the aircon, the increased pressure must have somewhere to go !
That way I got 300g out of the canister, so topped up with a second canister of R290 to 400g total.
