I have Jetta s 2018, I think the the air conditioner is not working probably because the cold air is not good in-spite of the back pipe of cooling system which is coming from cabinet is very cool, and the heating pipe which is coming from engine still bring hot water and it still circulation in hot radiator inside. THANKS
Sounds like there is a problem with your temperature (blend) door within the heating ventilation air conditioning (HVAC) system. Here's a sketch...
It sounds like the controller for the hot/cool blend door (which routes air to the hot heater core) is not fully closing when it should be. You are getting hot air off the heater core overwhelming the A/C cooling. See also this posting for more info.
One note: You might check the details of your 2018 Model Year warranty. It's possible that for HVAC system they use the time frame (and not the mileage) to cover that. A three year / 36,000 mile warranty wouldn't cover a driveline problem with 40,000 on the odometer, but paint and HVAC might be covered for 36 months regardless of the mileage. Please read the fine print on the warranty in the book in your glovebox. Note: all manufacturers are different on this stuff. Details may vary. Read the warranty!