Need help how to fine tune the old arduino brew pi

here’s the deal, i made a glycol cooler that will run on brewpi to ferment my beer. the glycol will be constantly pumpt thru the coil in the beer and be kept at the desired temp profile.

thing is i cant get my head around how to fine tune the brewpi.

this is how the graph look now


how do i get i to behave more stable. i just don’t know where to start. i’ve been looking in the fora but it seems all the info is for the new brewpi

The Arduino version of BrewPi has hardcoded minimum cooling times and the heater can only turn on or off, no PWM.
The Photon version would be able to cool and heat with less than full power for tighter control.

You can try to reduce Kp, but you will still have the minimum cooling and heating time.

That said, it is very strange that your fridge setpoint is in the wrong direction. What is your Kp? Is it negative? It shouldn’t be.

pwm isn’t needed the pump will always be on. i just need to get my head around the pid settings. i’ll adjust the kp and see what happens.
i’ll be very happy if i can get the temp swing withing +/- 0.3 of a degree

thanks for the input