Hello people, I've seen many of you (me included) with the same symptom:
The A/C system switches from vent to defrost mode under engine load (going uphill or overtaking another car).
It is caused by a vacuum leak and as far as I've seen most of us had the same problem a loose red hose, here are some pictures of where to start looking first.
This is the hose that gets disconnected from the back passenger side of the intake manifold.
This is where that hose should be connected to.
This is the other end of the same hose, it has a check valve on it and this side is connected to the vacuum reservoir and into the firewall to the dashboard to control the A/C system.
This image is just to show the location of the vacuum reservoir, you'll have to remove the cowl in order to see it properly, if you don't you can still reach the reservoir but it will be a bit hard since you don't have much space.
Here's the vacuum reservoir and the hoses from another perspective.
Hope this information helps in the future, I don't know if it would be a good idea for the administrators to stick this thread on the first page, what do you guys think?. Any questions please let me know!.
Best regards,
Oscar.