Now that I know what codes corresponds to what, I need to know what they mean!!

1 What is the Heater Core??

2 The evaporator core temp is what?
3 ECT sensor is coolant sensor? And is it in Farenheit for US models?
4 Refrigerant pressure... I won't worry about that one.
5 Software status of AC? Not a variable?
6 Version coding?? not a variable either?
7 What exactly is 22? the Battery volt? 99% of...? I do'nt understand?
8 And is the poly-V-belt the fanbelt? Is this helpful for telling me when I might need a new one? or have a problem with it?

Thanks to anyone who can help.

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)