Mazda CX-9 front and rear temp difference.

[VegasGMC]

I have a 2014 with 94k miles. This is a new issue. When I'm on the highway if I turn off the rear blower the front dash air temp goes up 15 degrees. When I turn the rear blower back on, the air is cold almost immediately. This doesn't happen in city driving. I don't know if this is related but another issue I've had is when on the freeway the vents will switch from front to defrost or floor to bi-level by its self. happens with heat and a/c. This only happens about twice a year. Thanks