I have been sitting here trying to figure out the problem. I hear u on the HEAT!! We are in Houston area and HUMIDITY is OMG! The A/C has a long delay I think, also for the first time it has a program to protect itself and thaw the freezing up factor. When very humid which is like now, it will be on for a while and then only fan runs, turns off and u hear the H2O run off roof. We also keep the shades down to keep the sun out as much as possible.
I also checked the BR when LR was on and felt a slight air in the vent, so they are connected. Can't really explain, just that the bath is the last vent in upper area connected to LR that u shud feel power of air on.
I hope u get A/C soon, feel 4 u
Prob with vent on oven, just found that it wud take a giant to open outside. DH is 6'4" and still had to get on ladder to open or close