User Manual

Sequence of Operation
Operation Diagram – RTU with Three Cooling Stages and Three Heating Stages.
15
Siemens Industry, Inc.
Application Note, App 14900
140-1231
2020-02-11
If HTG STG NUMBER = 3, the application controls HTG STG 3 (O/B) as follows:
● If IndoorTempEff is less than the switching on point of the third heating stage
(HeatingSp – 1/2 HeatingDB – StgDifHt*2), the third heating stage has been OFF
for at least the time set in MIN OFF, and the Inter-stage Delay (StgDlyHt) timer
has expired, HTG STG 3 (O/B) is turned ON.
● If IndoorTempEff is greater than the switching off point of the third heating stage
(HeatingSp + 1/2 HeatingDB – StgDifHt*2), and the third heating stage has been
ON for at least the time set in MIN ON, HTG STG 3 (O/B) is turned OFF.
Operation Diagram – RTU with Three Cooling Stages
and Three Heating Stages.
Figure 2: RTU with Three Cooling Stages and Three Heating Stages.
Fan Operation
AUTO Mode – The fan relay is energized upon a call for heating or cooling per the
operating sequence. When there is no demand for heating or cooling (none of
heating/cooling stages are activated) the fan relay is de-energized.
The fan will turn ON when one of the following conditions has been met:
● In Heating mode, when the compressor or stage of electric heat is ON.
● In Cooling mode, 15 seconds before the first stage of cooling is energized.
The fan will turn OFF only after the following condition has been met:
● The compressor and stages of electric heat have been OFF for at least 30
seconds.