I spoke with some recently who clued me in on something that's been bugging me...
... I've heard some reports that some 18 & 19-20 Classic trucks didn't need the ATC wiring to get the HVAC system (temp controls) to work correctly.
Apparently "other" 8.4 conversion harness sellers that our harness have sold UAQ/UAS upgrade radio kits have been sending them out with out any hardware support for Auto Temp Control (ie basic 8.4 harnesses) and telling customers to just use AlfaOBD to go through the Single Zone ATC programming steps to get the temp slider & blend doors working correctly (ie Dual Zone ATC first & then Single Zone ATC).
The problem with this is 2 fold & is a known issue for almost 2 years now ...
1st - The truck CAN NOT cycle the HVAC compressor on/off correctly without the extra cabin sensors ... the HVAC compressor clutch will stay engaged as long as the truck is running ... whether or not you turn off the "AC" button on the bezel... pop the hood and take a look.
2nd - You end up with the ATC "Auto" button on your hvac "Controls" screen that you can't use?
-- Posted Previously -- & top of the 8.4 Conversion thread --
2018 & 19+ CLASSIC OWNERS !
* It is NOT recommended to install a 13-17 RAx radio in a 2018 or 19 classic!
It 'can' be done but you 'CURRENTLY' can't get rid of Cellular System needs service error message at startup (unless using the recommended 2018/19 classic UAx radio, & you will need ATC w/UAx upgrades to avoid hvac blend door issues).
Ram 2019 Classic RA2 to RA4 Upgrade.
Gibbs' HVAC Issues w/UAS upgrade (fixed with ATC mod).
& Outback199 's 19Classic w/same issue at
post 138.
.