Do we need ISO 17025 certification to certify the freezer?

You asked 

Do we need that certification to certify the freezer?"

I assume you are referring to your company having ISO 17025 accreditation (it is not certification)? It depends on the customers needs. 

The requirement that could be applicable to your situation is that the client needs the performance of the device verification to be done by an ISO 17025 accredited laboratory. In that case, the accredited laboratory would have to be accredited for the specific scope (type of test) they require. There are various ISO and National standards and regulations related to fridges and freezers, depending on their purpose. For example, the National Health regulator could have requirements for storage and monitoring conditions for vaccines. There is difference between certifying the performance of a device on manufacture (technical specification) to assure stability and verifying and monitoring the operational performance. For example refer to WHO requirements https://apps.who.int/immunization_standards/vaccine_quality/pqs_catalogue/categorypage.aspx?id_cat=17 The customer must clarify exactly what they need.

Different vaccines require different storage conditions, provided by the vaccine manufacturers provide recommended storage temperatures for their products.

Regarding the tests performed and the certificate of calibration, see the CDC requirements as an example, at https://www.cdc.gov/vaccines/hcp/admin/storage/toolkit/storage-handling-toolkit.pdf

For ISO 17025 calibration report requirements, refer to the ISO 17025 document template: Calibration Report and Certificate Requirements Procedure at https://advisera.com/17025academy/documentation/calibration-report-and-certificate-requirements-procedure/