The DEFA control unit is "the heart" of controlling the DEFA WarmUp system. By using the control unit you are able to turn the WarmUp system on only for the few hours that are necessary. This reduces the consuption of electricity. The DEFA control unit is programmable, with a choice of three manual heating times or automatic operation. The control unit is also small enough to be easily fitted to virtually all types of dashboard. If preferable, it can be fitted to the sun visir, to keep it entirely out of sight. A specially designed harness mat makes the electrical connections extremely simple and virtually foolproof.

In automatic operation, the system measures the external temperature and determines the optimum heating start-up time. The control unit also displays the charging voltage of the battery, the outside temperature and has a built-in freezing-zone warning.