My Central Heating Works At Random

I made the efforts to change the filters which I do often. But the central ac unit is several years old; however, one day it started blowing much slower than normal so I suspected it to be the blower motor.

Which I replaced with new capacitor and that was fine till a couple weeks later when the heat was on auto a blowing cool air so having to troubleshoot what the problem is. my quick fix which works at times is to turn it up to 90 degrees till heat starts up then turn it back down an then it will keep up with it for a while...

I don’t know there is no consistency and I can’t trust it to heat up when I need it most