2013 RDX driver side warm air, not cool. Air mix motor is working, click sound, so I think the problem maybe lack the refrigerant.

 

Only the driver's side? How about the passengers?

 

passenger's side getting cool air, not sure if it's cool enough though.

 

To do it right, you'll need a set of gauges and know how to connect them and interpret the results. Messing with A/C systems can be dangerous...if you don't know what you're doing you can do a lot of expensive damage to your A/C and possibly some painful damage to yourself. Take it to a good shop and get it done right.

 

I think just go to auto store and buy this, to refill some r134

https://www.carcarekiosk.com/video/2...recharge_freon

 

Here is the A/C system test from the factory service manual

 

It is a pretty common failure of the blend doors on these Honda/Acura vehicles with two zones. I would look at that before jumping to refrigerant level.

 

How to check the blend door? Is this same as air mix motor?

 

I'm sorry, I don't know on this vehicle. I looked for threads about it. You can look at MDX threads. I did look at threads over on the Odyclub and it is possible low refrigerant
can cause the the difference in temps from one side to the other. I would open the link dave08902 posted above and go through the troubleshooting steps.