I have a freezer coldroom with two seperate systems.
A control panel for each system. One system has a conventional defrost timer with built in fan delay and an eliwell controller (stat only) ie 1 relay. There is an evap
termination stat as well.

The other system has an eliwell 974 controller - 3 relays fan def comp.

The problem is they defrost at different times. so one maybe cooling while the other is defrosting.

What would be the best way to adapt them to defrost together.

Many thanks andy