Quite commonly ill be driving along the the heater on (manually set) at say 24 degrees...and after about 20 mins of driving it seems to almost forget that i want to be warm and slowly the temp gets cooler and cooler until its barely luke warm air, so i whack it up to max heat and it warms up fully and then i put it back to around 22-24 and its back how it should be. its done it for the past year or so but just curious as to if anyone else has the issue??