Most motherboards (but not all) have basic protection for this, so it's quite unlikely that you break your motherboard electronically that way. That said, blow

Most motherboards (but not all) have basic protection for this, so it's quite unlikely that you break your motherboard electronically that way. That said, blowing compressed air at a fan will spin the fan much faster than what it was designed for. So you still risk breaking the fan mechanically. Always hold the fan when blowing compressed air at it.