Hi Guys
my neighbour has a 2011 Passat estate 2.0 SE with dual zone climate control. and has a double ended problem. back in the summer he was driving back from a holiday, a warm day he had the Climate set to 20c but no cold air was getting into the cabin despite the fan was running at almost full speed. opening the bonnet the aircon pipes are about an inch thick in ice. after a restart the cool air flooded into the cabin and has been working fine up to about six weeks ago. then just the oposite happened. cold day and had the climate set to 21c but no heat coming though into cabin. again after restart all was fine.

fast forward a couple of weeks same thing happened only this time restart did not work, however releasing the cap from header tank let out huge hiss of air. drove the car for 100 miles heat was fine. the following morning he got in started the engine and a warming popped up ""Check coolant"". on checking the header tank was empty. no puddle under car, all carpest in cabin bone dry. so topped up with approx 1 litre coolant. then for a couple of weeks all was fine heat was good and no coolant loss.

a fortnight ago same thing again no heat.. opened header let out air and some bubbling. 2 days later ""Check coolant"" again and needed approx one litre of coolant. plugged in with OBD scanner and no codes were recorded. and pressure tested cooling system and no leaks. done tets on oil and no water is present, checked coolant and no trace of oil. sniff test revealed no trace of fuel smell. i have disconnected pipes to heater rad and blown through no sign of restriction.

there is no loss of performance, economy is still very good at 66mpg on a 100 mile trip on the motorway. the car has about 60k miles and up to 2016 was dealer serviced when the dreaded emissions fix was installed. but not for long. a month after installation it was removed and returned to a factory state. since then a local independant has been doing service work. he has had a look on a couple of occasions but each time it was at a time when heater was behaving normally.

so looking for guidance / help. my neighbour is hoping to drive to Cornwall for new year to visit family. so i would like to make sure he is going to get there without breakdown if possible. hope there is an easy answer to this head scratcher.