Electrical problem solved
 

Thanks to all contributors who helped correctly diagnose my problem. To recap, my battery light was flashing on and off intermittently as well as the AC blowing hot then cold alternately. I can't remember their name but a member suggested I check the battery cables to see if they were getting hot which would point to the issue being a high resistance battery cable. I tested the car and sure enough the positive cable was heating up under load.

So, I bought a replacement positive battery cable from Jagdaim, via ebay, who make aftermarket jag parts to specification. The cable cost approx. $160 AUD. I don't wrench on my car as I live in a communal parking area with no workshop facilities so I paid an autoelectrician to install the cable. Total labour $160 AUD.

Took her for a test drive after cable change and she drives with no issues with the AC pumping.

Problem solved for a measly $320 AUD. Needless to say I am very happy! Thanks again to all those who offered advice in diagnosing the issue.

Dandy

Btw, it was Thermo with myself and Dennis Black concurring