Carrier 42V - Manual (Page 59)

59
Thermostatic 2-Pipe Auxiliary Electric Heat with Valve
Control — This system, also called twilight or intermediate
season electric heat, goes a long way towards solving the
spring and fall control problems of 2-pipe systems.
Chilled water can be run late into the fall, turned on early in
the spring and heat will still be available to all units whenever
required.
In winter the system is switched over to hot water. Two
changeover devices are required for this. One device switches
the action of the thermostat and the other locks out the electric
heat when hot water is in the coil.
With this system, the fan runs continuously unless manually
switched to OFF position. Fan must be on before thermostat
can send signal to open chilled water valve or turn on electric
heater.
Two control methods are available:
1. Use the standard automatic changeover thermostat with a
dead band between heating and cooling.
2. Use a manual changeover thermostat. With this method
only one changeover is required.
Be sure to include a 2-way or 3-way electric valve with this
system.
NOTE: Wiring diagrams are for 120-v power supply. If other
voltages for heaters or controls are specified, wiring may differ
from that shown. See Fig. 57 and 58 for line voltage control.
See Fig. 59 and 60 for 24-v control.
Fig. 57 — 42SG,SH,SJ,VA,VB,VC,VE,VF 2-Pipe Heating and Cooling with Auxiliary Heat —
Unit-Mounted Thermostat (Line Voltage)
a42-4066
120-V WHT ALL OTHERS BLK

NEC CLASS 1 WIRING