Hi folks!

I have a 2006 G35 sedan, 6MT.

A strange problem started recently with heater - if the rear defroster is turned on, the heater blows cold air, even when temp is set high.
As soon as the defroster is turned off, the warm air starts.

I don't remember this being an issue last year or any time in the past.

All other internal controls / functions work fine as far a I know (seat heaters, A/C, dash lights, etc.).

Any help / suggestions would be welcome please.

Thanks!