Question: I have a dell latitude 820. The fan was blocked for a while, after removing the crap (hair, etc.) the fan didn't work anymore. I tested the fan, but that part was OK. So I think the fan controller is broken. Which component is the fan controller?

Answer: 
If you are sure the fan is working then there isn't much that you can service. Not sure about your specific laptop but most have the fan controllers built into the motherboard so there isn't much to fix (beyond replacing the motherboard).

Are you sure the fan just isn't turning on because it doesn't need too? The d820 we have here doesn't run the fan very much and it is fine. I did find this utility which claims you can control your fan by software, this may help in troubleshooting if the fan is truly broken or if it just isn't turning on because the temperature is low.

[Dell Fan Control Software](http://www.iterasi.net/openviewer.aspx?sqrlitid=hzoigkl74kqrmccelopr-w)
I'm not familiar with the lattitude series, but as long as the fan is not the processor fan, you should be ok. You can get a lapcooler to place underneath the laptop for cooling if you are worried that it's gonna get hot. This is a fairly cheap (~$20-$50) solution that won't give you a headache with the anti-static straps and voiding warrenty by opening the case.