Unable to hit hot end temperature with part cooler on I'm unable to use the parts cooler I printed. Every time I turn it on, the hot end temp drops too low, and for some reason the PID can't seem to get it back up:



This is a test to simulate the issue. The first drop is the fan kicking on, then the last bump is me turning the fan off. It's almost as if the set point drops when the fan kicks in. Any ideas? The PID is tuned (I ran the autotune) and works well without the fan on. This is a RepRap Guru Prusa clone.
This effect you describe is a commonly known problem that occurs when the print part cooling fan is not correctly positioned, i.e. if it blows air directly onto the nozzle or heater block and is best solved by printing an alternative part cooling fan duct. Alternatively you could insulate the heater block with some insulation cotton or silicone socks that fit over the heater block.