[hvalentim]

Maybe, there isn't any major problem. (..)
You can do a small test with your LED's, with just a 9V battery(...)

Guess what. You are right. It seems it all derived from my misunderstanding of what I was observing.

While performing your suggested test I came to the conclusion that is was simply a problem with my improvised led connection. It turned out the led never blew in the first place.

I also came to the conclusion that I was figuring the way one should read voltage across a resistor the wrong way. You will only see a drop in voltage when a load is present.

Also, when the DHT22 is present no voltage is feed to the FAN. So I guess the IRLZ44N is doing what is should and it was just a matter of values assumed by the software when all sensors are absent.

So, this serves to prove:

1) that it may be safely said that I am prone to over-complicating matters

2) that my first soldering job ever turned out pretty well and it serves to prove that WeatherDuino can be successfully built by someone starting from a zero knowledge about soldering and electronics

3) that building a weather station may very well end-up being a side effect of a much more interesting endeavour: enlightening oneself on basic electronics.

Now, on to the RX unit...