What temp setting is the heater at? I'm assumeing its a bit higher than the instead airtemp. A temp fix might be to just turn it you till the display reads "high".If that doesn't work, whats the temp gauge doing? Does the air even get warm?
I have not done a coolant flushLike nm+ said set it in high and see if it dose work or your heater core is stuck with all those dirt build up in side the coolant. Did you ever do a coolant flush recently? If you did then it probably air bubble if not take it to the dealer and tell them to do the flush and they will connect it to a machine and force all the junk out from the whole system.
there are flaps that open and close behind the dash that constantly move to adjust the cabin temp.
there are little servos that controll them, they go bad.
hence no heat, it is stuck with the ac open.
instead of having a dial to change the temp on our car they control themselves.
if i had $$ id bet thats what it is.
you can manually open it by using some zip ties untill you really figure out what is wrong with the car and have heat in the meantime .
do i have to remove the radiono pics.
if the passat is the same as my A4 was they should be behind the radio on the passenger side, you have to find the 1 that controls the hot & cold air inlet flap.disconnect the thin metal cable and tie it open, if this is the problem which im pretty sure it is.once you find the servos just slide the one that does not move, you can figure out which one it is by using the controls to make the other 2 move(if i remember correct there are 3).
if you need more info let me know.