It is as designed, it is due to the enclosure anticipating the start of the blades, as normally the enclosure won't be ran with no blades installed. So when you power on the enclosure it starts the blowers waiting for you to start the blades. This is why you don't see the same thing when powering down the enclosure, as it isn't expecting the blades to be powered on when it is shut down.  May I ask why you're wanting to run the enclosure with no blades running?
Hi, I have a question regarding the PWM of the blowers in the VRTX. I have latest version of the CMC. When the chassis is turned on, but no blades turned on the blowers insist on running @ 20%. First I thought it was because I had AIC's installed, but it persist even if I remove the AIC's. As I can see from the design of the VRTX, the blower fans seems to be designed to cool the blades only and the fans the remaining parts. So why is it when the blades are turned off that the blower fans are still running @ 20%. I have set no offset for the fans and enhanced cooling mode has not been enabled. I would think the blower fans would either turn off or go even lower down in PWM. I know its possible to control the fans of dell servers in general via ipmi, but it seems like the CMC does not have an ipmi interface. Is there any way to make the blower fans run slower? Supposedly the VRTX should be able to be run under the desk, but I guess you have to be deaf to be able to handle the noise.
VRTX Blower PWM