I have a 2011 GT. On hot and humid days, once the AC has been running for about half an hour or so, the airflow through the vents becomes constricted. It still blows cold but it seems like ice is forming somewhere in the system and preventing air to flow through. If I turn it off for a while it goes back to working properly. No wetness on the floors or interior that I can find. Any ideas are appreciated. Thanks.