Resolved - Hotend temperature spike when Part cooling fan switches on?

[Crazy-Charles]

Whilst monitoring my prints via Octoprint i noticed that after the first layer was complete and the part cooling fan switches on the actual reported temperature spikes.

I can duplicate the issue by manually setting the hotend temp and then switching on the fan as shown below.

The autoreport feature also shows the same thing happening and shows heater power is switched on too.
Send: M106 S255
Recv: ok P15 B15
Recv: T:150.93 /150.00 B:31.73 /0.00 M:36.52 /0.00 @:127 B@:0
Recv: T:160.12 /150.00 B:31.71 /0.00 M:36.46 /0.00 @:127 B@:0
Recv: T:173.64 /150.00 B:31.51 /0.00 M:36.49 /0.00 @:127 B@:0
Recv: T:186.65 /150.00 B:31.43 /0.00 M:36.58 /0.00 @:0 B@:0
Recv: T:189.22 /150.00 B:31.32 /0.00 M:36.58 /0.00 @:0 B@:0
Recv: T:185.54 /150.00 B:31.33 /0.00 M:36.58 /0.00 @:0 B@:0

I am using MPC for hotend management.

Not sure if this is a "bug" or I have managed to break it whilst customising the firmware!

[Crazy-Charles]

Further investigations and tests I narrowed the issue down to the MPC Fan Coefficient setting, I had inadvertently put 0.969 as its value instead of 0.0969 in configuration.h.

So yep, I did break it but its ok now