Air con issue

[Vzalloyissues]

Hey lads and lasses, looking for some quick advice, I've got the leo alloytec, air con runs perfectly however when I accelerate the vents will switch from feet or face vents to dash vents and starts blowing hot, only lasts about 30 seconds before it corrects it self, any advice? Never seen this issue before

 

[Skylarking]

The VZ use vacuum to control the flaps and vanes within the bowels of the HVAc module.
So the question is whether vacuum accumulator can hold consistent during WOT?

@Fu Manchu’s pic in the linked thread below describes the system and may be helpful to you ( amazing what a quick google can find )…

https://forums.justcommodores.com.au/threads/vacuum-for-hvac-controls.292330/

PS: from the info Fu provides, it should be obvious no vacuum = demist, probably as a fail safe design. And many may know that WOT = no vacuum so I’d say either the check valve is pooped or the vacuum tank has a small leak that normally isn’t noticed while the engine produces vacuum.