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HVAC Forced Recirculation Mode –
From the factory, even when the user presses the “recirculate”
button on the HVAC controls, the recirculation mode door does NOT completely close. When the HVAC
is on recirculate mode, the fresh air door actually only closes about 90%. Roughly 10% of outside air is
still being pulled in. With the HVAC in Auto mode, press the recirculation button on the HVAC controls
(the vehicle with the curved arrow) 4x in a row. You will hear a chime, and might hear a slight change in
the blower motor/airflow sounds. To cancel forced max-recirc, press the “Auto” button on the HVAC.
My best guess on why GM programmed the HVAC this way is to: lessen the chance of CO poisoning (in
the event that exhaust gasses leak into the cabin), to prevent CO2 poisoning (the cabin is sealed
surprisingly tight, with 5+ occupants breathing inside, there is a remote chance CO2 levels could get
high, to prevent the cabin from getting stale/musty, or to improve AC performance. Under many
conditions, if AC is ‘too powerful’ and cools the cabin too quickly, it can cause the AC to short-cycle and
not dehumidify the air properly. This can make the cabin air cold and "swampy“, and even cause the
evaporator to freeze up.
The only time this AutoSync feature should be used is if you are in extremely dusty conditions and need
to completely seal the cabin. I do not recommend using it for an extended period of time. The feature
will default back to off every time you start the truck.
EFILive DSP-5 / EZ Lynk SOTF switching installation (2015-2016 LML only, L5P switchable tuning is
currently in development)
– AutoSync enables an alternative to engine tune switching that is much
cleaner and more attractive than the traditional rotary “knob”. The “DSP/SOTF signal” wire is a required
additional accessory (sold separately) in order for the AutoSync to utilize this feature.
https://www.btdieselworks.com/collections/autosync/products/autosync-dsp-sotf-wire
-Unbolt the OBD port from the dash bracket, and remove the top row blue plastic retainer clip using a
small screwdriver or pick. Insert the AutoSync DSP/SOTF wire into pin position 8 (top row, furthest
right…confirm with the small pin location numbers printed on the OBD port connector itself).
-Cut the “SIGNAL” wire going to your existing rotary DSP/SOTF knob switch. Usually this wire color is
purple or yellow, and goes to Pin 11 on the gray ECM “C3” connector. Splice the AutoSync DSP/SOTF
wire to the DSP/SOTF signal wire that you just cut. The ground (usually black) wire going to the old
rotary switch can be cut/taped off/removed.
BE SURE TO TRIPLE CHECK WHICH WIRES YOU ARE
WORKING WITH. SPLICING THE AUTOSYNC DSP/SOTF WIRE TO THE “GROUND” WIRE OF THE OLD
ROTARY KNOB SWITCH OR OTHERWISE INSTALLING INCORRECTLY WILL DESTROY THE AUTOSYNC AND
VOID ALL WARRANTIES!