I live in Texas, and it's hot as Hades here right now. My A/C has been running more or less non-stop for almost two weeks. With daytime highs between 102 and 108, it had been hot inside during the afternoon and early evening, but by midnight or so it would start to cool down and during the night and especially by morning, it would be really cool inside. In fact, the only time I adjusted the thermostat to turn the air off was in the morning. However, last night it never got cool inside. I woke up this morning with the covers still off; that's the first time all summer.
When I stood on a chair to check whether the air was cool, it did seem to be cool, but there also seemed to be less air coming out of the vents. I rent my house, and the hvac unit is pretty old. It's never been a powerhouse with respect to airflow, but it seems to be weaker than usual. I've been pretty bad about changing the filter every month (is that how often I should change it?), so the first thing I'm going to do today is get a new filter. I also looked at some youtube videos about cleaning both the outside (condenser) and inside (evaporator) coils. It doesn't look that hard. Is this something I should try myself?