Maybe this is a cheap copy of HP fans? Yours are genuine HP, or also genuine China made?
I checked, and it's exactly the same! Only difference is the code near triangle - mine is "7807a24R", "7808A24R". Looks like it's a serial number.
When I have time I'll go test. I'll get back to you with the results.
Ok. Then we'll see if it can be fixed via software. You can also try to plug it somewhere else like in motherboard and play with PWM value to see if you can really control them, to exclude the possibility of difference in avalon controller.
ADD:
Im starting to think that it could be a controller related issue.
I have controller v1.52 , and i can't stop the fans (for example) with option
--avalon-fan 0.
Which effectively mean, that in inverted pwm mode you can't reach max fanspeed.
Seems like controller can't pass low pwm values redefining it to some min_pwm constant, or have some internal regulation depending on sensor reading temperature ( i noticed that once fan rpm value was less than 2000 , but i can't set it now less than 2400, which is very strange )
It just my thoughts based on observation of b2 unit behavior, i would try to install fans later and see if i got the same issue as yours.
ADD:
I have found a "workaround". Seems that controller is indeed going into some "helper" mode to control the fans if the temp2 sensor is present. So i unplugged it, and seems that now i can control the fans like i want.
So, in short,
the solution is to unplug temp2 sensor! (closest to unit intake side)
ADD:
I tested new fans with temp2 sensor unplugged, it seems to be working as in b1 unit.