I got a used Circuit Specialists CSI 860 hot air rework unit. It seems to work OK, except when the power switch is turned off, the air goes on full tilt. Is this normal? I assume no because it then would have to be unplugged when not in use. I'm guessing that maybe, when turned off, the air is supposed to run for a bit to cool off the heater, and that maybe a timer is dead. This was a fairly popular cheapo hot air unit, so I'm hoping someone has one and can tell me how it's supposed to behave, if not what to fix. Photo of the unit is attached.