can anyone please help me! Under power the air conditioner blows through the defrost vent. Going to be driving through TX. next week....very hot!

 

Model year may help narrow down things.

Offhand, if I understand correctly - air comes out of the vents normally, except under heavy load / acceleration? If so, suggest you have a vacuum leak in the HVAC control lines somewhere. Finding it can be a chore - one of those handheld vacuum pumps can help divide and conquer the location of the leak - but still no fun.

Good luck, this is a tough time of the year for the A/C to not be going where it should - and keep us posted on what you find.