So, my air con works however, only when travelling at faster speeds or accelerating.

The air con doesn't often work at low speeds or will switch off when stuck in traffic.

Is this the known PCV issue or something else? 2015 Range Rover Autobiography 4.4 SDV8

Sounds like it. Does it takes ages to go cold too?
I had an Advanced Factors one fitted and all is good  Gone to a good home: 2011 4.4 TDV8 Vogue SE Buckingham Blue with Ivory and clear glass = "Rory"
2025MY Defender D350 90 in Silicon Silver on coils
1974 Series 3 Lightweight = "Millie"
Many, many other Landies over the years
My preferred specialist: www.glenrands.co.uk
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From a cold start up, the car takes about 5-10 minutes for the air con to kick in. It remains working so long as I'm driving at speed.

As soon as I get stuck in traffic, it just blows warm air after a few minutes. 2015 Range Rover Autobiography 4.4 SDV8

I thought it was called the RCV....

Anyway loads of info here...

https://www.fullfatrr.com/forum/topic43778.html? Pete
__________________________________________________
2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand Sold
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Sold
2002 L322 Vogue 4.4 V8 Epson Green (Fatty Offroader) Sold
-Click for Project Fatty off roader-

It could also be a low refrigerant charge. It'd be worth getting it recovered to check the charge weight against spec.before jumping in and replacing the RCV.