I have a fault on my citroen xantia 1.9 TD SX with air con and climate
control, when the heater is on full and the blower is on any position but
lets say full on, the temp out of the vent is fairly warm, but within about 5
seconds it cools right down no matter what temp setting it is on it always
cools right down BUT every now and then it stays a little warmer showing this
is not a consistant fault. I have had the car conected to the citroen fault
diagnostic machine but there was no fault shown other than the sensors in the
vents and the ambient temp sensor showing way too high, so i changed the
sensor but the fault is still there. I also removed the device that controlls
the flap that allows heat into the vents thinking the vent was not opening
fully, I manually altered the flap but this made no change. When I first
encountered this problem I thought the heater matrix was blocked but I am not
convinced of this as every time I flush out the matrix it is flowing fine and
the water is usually quite clear.

Any help would be greatly appreciated
Thanks
         Phil