Carrier 48MA - Manual (Page 19)

In this system, the MUR is energized by the NS
controls. This opens a set of normally closed
contacts and shuts down the unit, including indoor
fans. The outdoor air dampers are also closed by
the MUR. Cooling lockout is attained by energizing
the MCR. Energizing these relays turns the unit off
and the NS system seems to work in reverse.
A cooling thermostat is used on heating NS.
When temperature rises, the thermostat, in series
with the night switch, energizes the NS relay. Its
contacts close and, in series with the time clock
contacts, energize the MUR. As the space tempera­
ture lowers to the NS setting, the NS thermostat
de-energizes the NS relay which de-energizes the
MUR, turning on the unit.
Again the day/night switch overrides the NS
clock and heating can occur because the NS relay is
de-energized. The factory jumpers remain across
CL and NS terminals.
*CONNECT HERE INSTEAD OF NS
TO CYCLE INDOOR FANS
CL — Cooling Lockout
MUR — Master Unit Relay
NS — Night Setback
DAY/NIGHT SWITCH
Fig. 20 — Night Setback, Method #1
SWITCHES SHOWN IN NIGHT POSITION,
rT? m n? m
I A I 1 A| I A I I A|
II5V
FIELD
SOURCE
note : 24V WIRING
BETWEEN CONTROLS
NIGHT SETBACK
THERMOSTAT (COOLING TYPE)
, I-------- T~1
LEGEND
APS — Air Pressure Switch
FRS — Filter Media Runout
Switch
MCR — Master Cooling Relay
MHR — Master Heating Relay
MUR — Master Unit Relay
c=iOR(^ Terminal (Circuit Board,
Field or Accessory Conn )
------------- Accessory or Field Wiring
-------------- Factory Wiring
------ ------- Circuit Board Run
i cb
HI H2
ACCESSORY BOARD
ON BASE UNIT
REMOVE JUMPERS BETWEEN
NC AND R: C AND W
Fig. 21 — Night Setback, Method #2