What is the correct minimum fan speeds of the early 2009 iMac?

[poiihy]

I need to know the correct fan speeds of an early 2009 iMac but there is no info out there.

The minimum fan speed(s) of my iMac seem to be changing. Sometimes the ODD minimum is 1650, sometimes 1350, and sometimes 5100.

 

[poiihy]

Also, another question;
What are each of these temperature sensors in this list? Are any sensors bad and reporting incorrect values?
This is Psensor in Ubuntu.
As you can see, sensors TG0D, TG0H, and TL0P report temperatures of -127 and -128 degrees celsius.

 

[poiihy]

I probably should mention that my ODD and CPU fans run at full speed. I have to set the speeds down with Macs Fan Control if in OS X or in the Terminal if in Ubuntu. I assume they are just dirty by dust.