no heating or cooling medium flows through heat exchanger 1 1 for example if the heating cooling control 20 is disconnected for example by interrupting heating of dye through or vat 1 the module 20 provides an output signal at line 20 1 which is applied to the temperature command monitor 12 and to the temperature programmer 10 a switching signal from terminal 20 2 is also applied to control transfer of selector switch 9 to the broken line position so that temperature program integrator 11 will then be controlled by a search program cycle within unit 10 and by the temperature command monitor 12 rather than by comparison at 7 of the actual dye exhaustion rate signal 6 1 with respect to the command signal nominal exhaustion rate applied at terminal 7 1 the output from integrator 11 applied to temperature controller 19 through combining comparator circuit 17 1 then can be utilized to reconnect module 20 for example by initiating a cooling cycle subsequent to a heating cycle as for comparison of the actual result obtained by comparator 7 a typical heating and cooling cycle is shown in fig5 the control system of the invention incorporates apart from its main facility i e control of the exhaustion rate a conventional preselectable temperature program with high regulating accuracy for a preheating phase a predetermined temperature can be selected with maximum heating up rate and this be maintained constant over a variable holding period the dyestuff exhaustion phase can be preselected through the described exhaustion control system but should this not be utilisable the system can be run with a temperature program and two selectable heating up rates minimum heating up rate 0 2.