Replace furnace blower or entire furnace/retrofit AC
We really haven't noticed any significant problems with the heater pushing heat through the vents but that might not be true since we keep the heater down at like 60-65. I had a tech come in when we moved into the house and he said that he was surprised that our 30+ year old furnace was working so well. I think he said when he tested the temperature, it was getting up to 550. He said if there was any sign of it going bad, it would be much lower. Who knows.
We have noticed a major problem with the AC and we've just been living with it. It seems like our AC doesn't cool the house down past 78 or so degrees. For example, last week it reached the 90s and we kept the AC set to 78. It runs constantly and the temp stays at 81-83. When it's around 80s outside, we can set it to 78 and it will have a hard time and will run steady for a few days but WILL eventually reach 78. The vents don't appear to output much air on the farther parts of the house and it is a few degrees warmer in those rooms. I talked to the same tech about this when he came to prep/test the heater for the winter. He said that it was strange that someone put a return on the other side of filter in the duct. He said that the ducts might need to be replaced even though the AC is semi-new. We have a newer AC unit outside which is from 2004 and hasn't run hard since about 2007 or 2008. The house was on the market for 2 years unoccupied and we mostly keep the AC off since we've had problems with it.
I was reading a few other threads on here. And I decided to try to open the blower box while the blower was running. Someone at the farthest vent said that it produced a significantly higher air output. I read that might indicate inadequate supply.
I also read that I might try taking the blower fan apart and cleaning it thoroughly. I tried to decouple the fan from the motor, but couldn't. It appears the fan is seized onto the motor. It was pretty rusty around the post, so I tried to spray some rust penetration onto it and let it soak. It's still stuck and now it's leaking what looks like a gray, thick liquid/oil from around the post very near the fan. Is the motor/fan scrap?
If the motor/fan is bad, should I replace them? I'm worried that if I need to replace the furnace that the new motor/fan wont be compatible. I'd hate to spend several hundred on the blower parts only to have to replace the whole works in a few years. I read that getting a bigger blower/fan won't work to push the AC out to the farthest vents since it'll produce too much static and won't be efficient enough.
I'm in the very early learning stage of this whole furnace ordeal. However, I'm a pretty smart person and I consider myself to be pretty handy too. I just need a push in the right direction.