When you suspect that there is an issue with your central heating and air conditioning system, do not ever try to figure it out yourself.
Sure you can troubleshoot.
But if the troubleshooting does not bring any answers, it is best to call the local heating and air conditioning company to send out a certified heat and a/c specialist to evaluate the situation. That is the best way to go with it. If you try to repair a central heating and air conditioning system on your own and you are not a certified heat and a/c specialist, chances are you are going to cause more damage than good to your HVAC unit and it may even cost you the steep price of having to buy a brand new and totally up to date central heat and a/c unit when it is not really needed! You need to just call that local heating and cooling company anytime you suspect something wrong with your HVAC unit. I had a buddy I knew once who tried to play guessing games and repair their own central heat and a/c system and they ended up completely killing it all together. They had to dump thousands of dollars into a new heating and air conditioning system unit because of them not calling the heat and a/c company to come and have a look at it and fix it. After hearing that story I made it a point to never try that myself and just spend the money to have the heating and cooling professionals do all the HVAC work needed.