JeepaRoo

has anyone with a 2011-2014 that has a rear-defrost button on their HVAC had it flash?

my JK just started doing this when I first start it up the rear defrost light flashes for a minute, sometimes 2 minutes, and I have no HVAC function.. note NO A/C...

once the light goes out everything works as normal...

it only does it if the jeep sits for at least 30 minutes or so before restarting.. if I shut it off and restart it right away or within a few minutes all works as normal with no flashing light..

I tried doing the battery disconnect and touch the terminals together trick.. no change.

I didnt see much in alldata about it.. and I dont have the chrysler scantool to get in and play around.
-Christopher

w00dduck

I have a 2013 jk. Mine does the same. I have been to a local dealer and they don't know what could be the cause. Searched a couple of forums and still no answer. I guess we just going to live with it lol.

Jiblet

The flashing light is the system testing itself or trying to recalibrate the blend door.
It's called the EBL status indicator. (EBL is Electric back light or something, means the rear window defroster)

Seems you may have a malfunctioning blend door or other climate control problems.
There is a way to get climate control specific codes.
I don't know if you need the SCANtool or not on the JKs.

JeepaRoo

thanks for the info.. off to the dealer it will go.. im guessing it must need the dealer scantool.. my own scantool didnt bring up any codes.. maybe because whatever its doing it eventually gets past it doesnt set a code.. once I get past the first minute or two the HVAC works perfectly

-CHristopher

bushpilot

Mine does it too - and considering that my soft top has no rear defroster i doubt its related to that.

Jiblet

Someone posted this (on a Dodge forum) regarding using the SCANtool to recalibrate:

HVAC Door Recalibration is started by selecting the following from the DRBIII(R) menu: Select HVAC, System Tests, and HVAC Door Recalibration. Allow the test to run to completion before proceeding.

Let us know what the dealer says/does. Good luck.

JeepaRoo

took it in, and the Issue occured but wouldnt give them any codes..

they contacted chrysler engineering which said that the HVAC controller is losing its calibration after a short time being powered off..

the background....
when starting the jeep it has to go through its own internal air door calibration routines.. which I guess involves running the doors from end to end and taking encoder readings along the way. the encoder is what tells the HVAC control head what position the doors are in. the motors on the doors slowly drive the doors from end to end (stop along the way depending on position called for). the doors control the amount of Heat-mix (temperature knob).. and the air-mode ..(floor, def, etc).. they are electrically driven (not mechanical or vacuum)..

normally this calibration operation is only performed once on a new install of a control head or by a scan tool. the values are supposed to survive key cycles and jeep power-off (battery disco) conditions.. in my case that non volatile memory is not working.. so the jeep recalibrates every key cycle.

they are ordering me a new HVAC control head under warranty.. (jeep is just 12 months old at 9000 miles)..

the rear defrost button is present on jeeps built as soft-top only models with the power convenience group which includes power heated mirrors.. the mirror heat is activated by the rear defrost button... so alas why us soft-top jeepers have it.

on jeeps without the rear defrost button, this same condition will be recognized by a sizable delay after starting the jeep until the HVAC begins to operate (1 -2 minutes).
wil post back here once they put the new parts on.
-Christopher

Jiblet

I'm glad they figured it out for you. Good luck. Thanks for the update and the info.

rplst8

Is the HVAC control head just the module below the radio with the three HVAC control knobs? Or is it some unit located somewhere else in the dash?

JeepaRoo

yes thats the control unit.. there is a CAN connection from it to the main Computer but for the HVAC this is the part that goes bad. . (if thats what it is).. I guess a bad driver motor feedback can also cause the light to flash as well.
-Christopher