Does the freezer need to be on the flow chart as a preventative control

Does the freezer need to be on the flow chart as a preventative control

If you mean HACCP flow, yes it needs to be there and risk assessed- normally part of your prerequisite program.

Would have to see more of your process to know if your freezer is a PC, maybe for you it's just a step in the process

However, ALL steps need to be included on your flow chart, regardless of PC, CCP or a simple process step

Yes

Does the freezer need to be on the flow chart as a preventative control

If you're storing material in it that alone will put it on the flow chart. 

If you're making a claim that your storage temperature is preventing spoilage or pathogen growth, that would be a fairly standard biological preventative control.