Carrier 50DL - Manual (Page 15)

Fig. 20 — Setting the 7-Day Time Clock
NOTE: Dial turns clockwise when power is
connected and time clock is operating.
2. Hold tripper firmly against the edge of dial and
tighten knurled screw by hand. (Do not use
pliers.)
3. To set OFF (UNOCCUPIED) operation, use
OFF tripper and repeat steps 1 and 2, setting
the time desired for the switeh to turn off.
(Normally open contacts open and normally
closed contacts close.)
4. Time cloek can be set for up to 3 ON-OFF oper­
ations per day or 21 per week. To omit operation,
do not place trippers on the dial for that day(s).
NOTE: Minimum time from an ON operation to an
OFF operation is 3-1/2 hours.
Minimum time from an OFF operation to an ON
operation is 3-1/2 hours (limited by the width of the
trippers which cannot be set closer).
Setting the Time of Day (Fig. 20)
1. Apply power to timer motor.
2. Turn time dial clockwise until the TIME pointer
is aligned with correct time and day. Do not
turn time dial counterclockwise and do not
move the TIME pointer.
Time clock has a spring wound carryover me­
chanism to keep timer on schedule during power
failure up to 10 hours. When power is restored,
mechanism automatically rewinds.
VARIABLE VOLUME OPERATING SE­
QUENCE (with accessory electric heat) — Clock
in remote control box switches controls to DAY
(OCCUPIED) mode. Indoor air fan runs for one
minute before any other control can function. (This
allows sensing of unit discharge air to start from the
conditioned space ambient rather than initial unit
ambient.)
If return air is below adjustable set point of first
stage of the morning warmup thermostat, heaters
energize. Outdoor air dampers remain elosed.
Normally open contacts in base unit override the
field-supplied VAV terminal controls and room ter­
minals remain open during heating.
When first stage of morning warmup thermostat
is satisfied, heaters shut down, indoor air fan runs
eontinuously and outdoor air dampers remain
closed.
When conditioned space temperature rises to
adjustable set point of second stage of morning
warmup thermostat, unit switches to COOLING
mode. Outdoor air dampers go to at least the mini­
mum position. (Once the unit has gone into cooling
mode, heat cannot come on during OCCUPIED
time period set on the clock.)
If outdoor air enthalpy is below setting of
enthalpy controller, economizer modulates open.
(If outdoor air enthalpy is above enthalpy set
point, economizer remains at minimum position.)
Economizer acts as first stage of cooling, providing
“free cooling” with outside air. If outside air alone
eannot satisfy cooling requirements of the condi­
tioned space, economizer cooling is integrated with
mechanical cooling.
Compressor(s) will start, stop, load and unload
and economizer will modulate to maintain an
average discharge air temperature. If outside air
temperature drops below the adjustable setting
(normally 50 F) of the low ambient lockout, the
compressor(s) will shut down.
At end of DAY (OCCUPIED) mode on the clock,
unit enters the NIGHT (UNOCCUPIED) mode.
The outdoor air damper closes and indoor fan and
compressors shut down.
If a field-supplied night thermostat is installed
in the conditioned space, indoor air fan runs only on
a call for heating or cooling. Dampers open only on
a call for cooling. On a call for cooling, economizer
cooling occurs first and then integrates with me­
chanical cooling to meet the cooling requirement.-
A 5-hour, manual bypass timer is provided in
remote control box. This timer, when manually
set by building occupant, overrides the UN­
OCCUPIED mode and places unit in OCCUPIED
mode for up to 5 hours.
Constant and Variable Volume Units
TIME GUARD® CIRCUIT — Timer sequence
for a particular unit depends on unit and com­
pressor arrangement. The Time Guard device pro­
vides a delay in compressor start-up after thermostat
closes. On normal unit start-up, outdoor air fans
energize 15 seconds before the compressor. If com­
pressor shutdown is due to satisfied thermostat or
automatic resetting of a safety device, the com-
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