So my son has been playing the clarinet for a month now and he's been doing really well. No issues with the notes, however over the holidays he started playing it again and he was having some issues on note C. He said it's taking more air than usual to produce a note and most of the time the note is not great. Or he said that it almost feel like blowing into a wall. I have cleaned it and not sure what is causing the issue. Any tips is appreciated.

I assume you mean 3rd space C over the break. Do the other "pinky" notes work well (left & right pinkies, B,C#,Eb)? If so, there may be a pad problem with the C key. If D works and there are problems with more than just the C key then his finger(s) may be pulled a bit off the tone hole(s) when the pinky(s)is down. Or, something else wrong with the alignment?

Thank you for your response. I actually found out that it was missing a pad on one of the back keys. I bought the kit through Amazon and will just do a temporary fix for now. I'll have to do full re-padded later date. I contacted the store that sold it to us and it just over the limit for warranty. =(

The clarinet is a complicated machine requiring regular maintenance. You should expect things to go wrong from time to time, and when they do, you should take the clarinet to a professional (unless you yourself are specially trained in this field and own special maintenance equipment).

You can a pad that fell out back in by using a match to make the glue soft. Much better idea is to get a tube of pad cement. Also, an assortment of clarinet pads of various sizes.