You might be suffering from eustachian tube dysfunction. Eustachian tube equalises pressure between your ears and yours nose , at times negative pressure behind the ear increases due to tube dysfunction. When you are exposed to ac the tube is unable to balance pressure behind your eardrum which leads to eardrum retraction and ear fullness.
Next Steps
monitor ac temperature , you can try some maneuvers to relieve pressure such as toynbee, where you need to punch your nose and swallow.