Recently purchased an HP c640 G2 chromebook. I noticed that the fan was rather noisy, especially when plugged in. I was able to address the problem using ectool.
(Warning, adjusting these settings may cause damage to your chromebook, shorten its lifespan, or void the warranty, you are fully responsible for anything that happens as a result of you following this guide)
To get information about the thermal sensors I ran
catloaf@paloma:~$ sudo ectool temps all
--sensor name -------- temperature -------- ratio (fan_off and fan_max) --
Charger 330 K (= 57 C) 56% (313 K and 343 K)
PP3300 Regulator 315 K (= 42 C) 13% (313 K and 328 K)
DDR and SOC 319 K (= 46 C) 30% (313 K and 333 K)
Fan 312 K (= 39 C) 0% (313 K and 333 K)
Under load:
catloaf@paloma:~$ sudo ectool temps all
--sensor name -------- temperature -------- ratio (fan_off and fan_max) --
Charger 332 K (= 59 C) 63% (313 K and 343 K)
PP3300 Regulator 314 K (= 41 C) 6% (313 K and 328 K)
DDR and SOC 321 K (= 48 C) 40% (313 K and 333 K)
Fan 311 K (= 38 C) 0% (313 K and 333 K)
As you can see, the temperature of the charger chip is causing the fan speed to ramp up even when the cpu isnt hot.
To address this I first get the default fan values for the various sensors:
catloaf@paloma:~$ sudo ectool thermalget
sensor warn high halt fan_off fan_max name
0 0 351 353 313 343 Charger
1 0 341 343 313 328 PP3300 Regulator
2 0 341 343 313 333 DDR and SOC
3 0 341 343 313 333 Fan
(all temps in degrees Kelvin)
And then I adjust the charger sensor fan_off and fan_on values to be 10 degrees hotter
catloaf@paloma:~$ sudo ectool thermalset 0 0 351 353 323 353
Now the charger chip being slightly hotter than the rest of the system is not causing the fan to ramp up, the system is now much quieter when idle.
catloaf@paloma:~$ sudo ectool temps all
--sensor name -------- temperature -------- ratio (fan_off and fan_max) --
Charger 327 K (= 54 C) 13% (323 K and 353 K)
PP3300 Regulator 313 K (= 40 C) 0% (313 K and 328 K)
DDR and SOC 317 K (= 44 C) 20% (313 K and 333 K)
Fan 311 K (= 38 C) 0% (313 K and 333 K)
Even under load the charger sensor does not get much hotter than it did before and the system is much quieter:
catloaf@paloma:~$ sudo ectool temps all
--sensor name -------- temperature -------- ratio (fan_off and fan_max) --
Charger 334 K (= 61 C) 36% (323 K and 353 K)
PP3300 Regulator 315 K (= 42 C) 13% (313 K and 328 K)
DDR and SOC 322 K (= 49 C) 45% (313 K and 333 K)
Fan 311 K (= 38 C) 0% (313 K and 333 K)