We took our rx350 into the dealer to have them replace the battery (Advanced Auto said they couldn't do it because the computer had to be reset) . Afterwards the A/C started acting odd. It was working fine prior. Now, after starting up, the A/C won't turn on (even the fan, etc) until maybe a minute later. And now the passenger side also blows hot air when it should be cold. We took it back to the dealer, and they said the air mix motor was malfunctioning. But from what I've read on Club Lexus, that doesn't really explain the delay in it turning on. I also saw a post which indicated not resetting the computer may affect the A/C. Thoughts? Any input is appreciated!

 

The person at Advanced Auto was a poorly informed and or an idiot. BMWs need to have the computer reset, not old Lexus vehicles.
I never heard of a need to reset the computer on the 3rd gen RX after changing the battery. I and others here have replaced our batteries more than once and never had to reset anything except maybe the clock.
I think the dealer may have sabotaged your vehicle to create more work and make their repair sales quotas for the month. Or it could be a coincidence.
However the one minute delay is pretty normal for the RX or any Toyota-Lexus in my experience.

I would disconnect the battery cables for 15 -30 minutes then reconnect them and hope everything resets back to where it was with the old battery.
If that is too much for you to do, then take it to an independent shop to be evaluated.

If you need to find a good independent repair shop start by searching this database then cross check any likely shops on Yelp or Google https://www.cartalk.com/mechanics-files

 

As mentioned above, no computer reset is required for battery replacement in the 3rd generation RX350s. So many people working in the big box auto parts stores simply do not know what they are talking about.

 

Unfortunate coincidence.