Carrier 48MA - Manual (Page 16)

The cooling load for this comparison is the
internal load (lights and people) minus the negative
transmission at the changeover temperature (48 F).
To determine the percent cooling load, compare
this value to the unit design cooling capacity.
Night Setback — Niglit setback control can be
added to a 48MA/50ME unit using field-supplied
components. There are 3 sets of terminals on the
accessory section of the unit zone control board
(see Fig. 18). The terminals are used in combina­
tion to achieve the system desired. Terminal sets
are: cooling lockout (CL), night setback (NS) and
“Short To Close Dampers.” Red jumpers are
factory wired across CL and NS; “Short To Close
Dampers” are bare (see Fig. 19). If the circuit
between CL terminals is broken, 115-v power to
the compressor control circuit liquid line solenoids
and economizer thermostat (if used) is shut off. If
the circuit between NS terminals is broken, 115-v
power to the zone control transformers is shut off.
By replacing both jumpers with appropriate
switches and connecting proper switch across
“Short To Close Dampers,” NS control is attained.
Although many versions of NS are possible, the 3
most common methods are detailed here.
METHOD NO. 1 - HEATING NIGHT SETBACK,
COOLING LOCKED OUT, AND CONTINUOUS
INDOOR EAN OPERATION
This automatic NS system requires a Honeywell
S659A seven-day timer, a Honeywell R8227B fan
center (night setback relay) and a Honeywell
T822D thermostat (heating type) 24-v service. In
this system (see Eig. 20), when the timer reaches
the “Night” position, the switches are as shown.
CL opens, dampers close and NS opens. The fan
continues to operate.
As the temperature falls, the NS thermostat
located in the average temperature space energizes
the NS relay (fan center) which in turn energizes
the zone control transformers. The individual
zones then heat until the NS thermostat is satis­
fied. The dampers remain closed and cooling is still
locked out. If a day/niglrt switch is used, the NS
thermostat is overridden and heating is controlled
by the normal thermostats.
Accessory remote panel assembly and/or ac­
cessory economizer may be used with this system
if desired. Cycling indoor fans with NS thermostat
is possible if the accessory remote panel is not
used. Connect the field wiring to the MU terminals
instead of the NS and the indoor fan contactor will
cycle with the heaters. Although this system does
not provide a time off delay for the fans after
heater shutdown, test experience indicates that this
is not a problem on these units.
METHOD NO. 2 - HEATING NIGHT SETBACK,
COOLING LOCKED OUT AND CYCLING IN­
DOOR EANS
This system requires a Carrier remote control panel
assembly 48MA900041, Honeywell S659A seven-
day timer, Honeywell R8227B fan center (night
setback relay) and a Honeywell T822C thermostat
(cooling type).
The number of candidate systems for NS
increases with the use of the remote accessory
panel. A typical system is shown in Eig. 21. The
use of the master unit relay (MUR) and the master
cooling relay (MCR) requires 24-v wiring only.
Installing the timer and the NS relay in proximity
to the remote control panel results in all wiring
being located inside the building in one area.
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