12
CONTROL SEQUENCE
A built-in microprocessor in the chiller-
heater controls the external pump
demand signals in response to the
cooling and heating load. The operating
sequence of each pump and the cooling
tower fan after start-up, during normal
operation, and after a normal stop or
abnormal shut down is shown in Fig. 10.
It is important that the chiller-heater have
control over the pumps to allow for
controlled shut down under normal and
abnormal conditions.
Running the chilled water pump at all
times is discouraged as the chiller-heater
logic will expect to see the flow switch
open when the “P” dry contacts are
opened. If it does not open, the chiller
assumes the flow switch has failed and
will generate error code E016.
Fig. 10
– General Control Sequence
CP = Cooling Water Pump Demand Relay
CTF = Cooling Tower Fan Demand Relay
P = Chilled/Hot Water Pump Demand Relay
