EarthLinked SCWD-024-1C, Quick Start Instructions

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SCWD-QS (12/16) Page 62
Appendix B : Functions of the Nano-PLC
Programmable Logic Controllers (Nano-PLC) come standard in all Prime Series units as well as in
the Classic SDH, SCW and SCWD. The Nano-PLC is programmed to ensure different functions
depending on the units; you can find a detailed description of these functions below.
Functions of SCW and SCWD systems equipped with the Nano-PLC
(Hydronic Heat/Cool):
SCW and SCWD units keep the same functions as always for installation and use. The Nano-PLC
simply replaces the analog hardware and adds two performance assurance functions:
1) Performance assurance: There is a 20-second delay on the low pressure switch before it can
set a lock out to prevent early cooling season nuisance calls. The “X” terminal is now a true 24
volt output and enables proper fault indication. Lastly, the compressor is delayed on startup for
10 seconds after the circulate pump starts to ensure that good water flow is established prior
to the compressor starting.