Right side fan running at only 200-250rpm, despite being set to 4000

From this tidbit of data its hard to say why you have a slow fan. You need a bit more diagnostic information to isolate this down. It could be the fan, the sensor on the fan or even SMC services that has an issue just for starters.

First are you up to fixing your system your self? If you are, do you have the needed tools and ESD mat & strap?

If you do, the first thing here is to open the system and do an inspection. You are looking for dust buildup internally on the logic board, fan and heat transfer fins of the heat sink.

If you do see buildup carefully brush the dust off with a small paint brush being careful not to snag it on anything then using a can of can'ed air blow out the loose junk. Don't forget to clean the fan blades and don't blow the air too hard or long on them as you can damage the bearings.

I would also recommend a better tool here to monitor things. Go to the App Store and checkout Temperature Gauge it will give you much more info on what is happening with your sensors and fans.