My AC will slowly grow weaker and weaker until it stops blowing. Then suddenly it will come back full blast. Happens once or twice a day. Ideas on what to check?

 

You may need a capable scan tool to check the system if the vehicle has automatic HVAC system.

 

My 2015 Sonata is doing the same thing! And My previously owned 2014 did same thing before it was totaled. To get mine to work, I have to hit the underside of passenger console for the blower to start working. Shocked that this flaw has not been addressed by Hyundai that I may never buy from manufacture again. I’m interested to hear how your issues turns out.

 

It was the blower motor. Not too difficult to replace.

 

Many vehicles will have the blower motor run on low speed in order to maintain a positive cabin pressure. this could be one reason for the blower motor requiring replacement earlier than one might expect.