Carrier ZONE-MIZER 50ME - Manual (Page 32)

Electriccü data
(cont)
Operating sequence
When unit power is on and no zone thermostat is calling for
cooling or heating, the indoor air fan and crankcase heaters
are on. The outdoor air dampers are at the preset position,
the burner pilots are lit and the forced-draft fan is on.
Cooling — On call for cooling from a zone, compressor no.
1 with 2 unloaders starts; a liquid line solenoid for that
zone evaporator coil(s) opens and outdoor air fan motor
no. 1 starts. Compressor will load or unload in response to
suction pressure as required. If additional cooling is re­
quired (i.e. more zones call for cooling), compressor no. 2
(no unloaders) will be energized and cycle as required.
If the heat load is not sufficient to maintain operation of
compressor no. 1 in an unloaded condition, the hot gas
bypass valve will meter hot gas to the outdoor air evap­
orator coil to supply additional load The Motormaster®
head pressure control will vary speed of outdoor air fan
motor no. 1 to regulate the airflow across the condenser
coil.
As required, outdoor air fan no. 2 (and no. 3 on 034 and
040) will cycle on and off in response to head pressure via
a fan cycling switch.
■ Gas heating — On call for heating from a zone, the gas
valve is energized. The heat exchanger for that zone will
be at full-rate firing. Reheat humidity control can be
achieved by wiring a humidistat in parallel with the cooling
thermostat. If zone temperature drops below setting of
heating thermostat because humidistat is closed, heating
mode will be energized to maintain zone space temperature.
Electric heating — On call for heating from a zone, the
first-stage heating relay activates the first-stage contactor
which energizes the first-stage heating clement. On call for
additional heating, the second stage of the thermostat
activates the second-stage relay, contactor and heating
element. If unit has 3-stage heat, the third (last) stage of
heat can be energized only if the outdoor air temperature is
below the outdoor air thermostat setting (adjustable). If the
outdoor air temperature is above the outdoor air thermo­
stat setting, the last stage of heat is locked out on all zone
modules. The heating elements are connected so that the
load on the 3-phase power supply is always nearly balanced.
Electric heat lockout — If any zone module is operating
on mechanical cooling (compressor is operating as de­
scribed previously) one heating element in each zone
module is locked out and cannot be energized.
Hot water/glycol heating — On call for heat from a zone
thermostat, the heating relay and heating coil solenoid valve
for that zone are energized. If 2 or more zone modules are
joined to serve a common zone, stage 2 of the heating
thermostat may be used to provide staged heating capacity
control.
Reheat humidity control can be achieved by wiring a
humidistat in parallel with the cooling thermostat. If the
zone temperature drops below setting of heating thermo­
stat because humidistat is closed, heating mode will be
energized to maintain zone space temperature.
Modulating outdoor air control (economizer) — When
outdoor air temperature drops to outdoor thermostat
setting (55 F adjustable), the compressors are locked out.
When a zone calls for cooling, the mixed air thermostat
(58 F adjustable) modulates the outdoor air dampers to
permit cooling with outdoor air.
Exhaust air dampers — When unit is in economizer
mode, the exhaust relay energizes the outdoor air fans at
full speed As the outdoor air dampers open and the return
air dampers close in response to the mixed air thermostat,
the exhaust air dampers open to permit power exhaust of
returning indoor air.
Roll filter — As filter media becomes clogged, an air
pressure switch activates a drive motor to automatically
advance clean filter media into the return airstream. A
filter light can be used to indicate that filter media roll has
been expended.
Remote control panel — This central station control will
operate the unit or override zone thermostat settings to
lock out heating or cooling. Panel has a DAY/NIGHT
switch and a damper position knob for in-space central
^ control of these functions, and a FILTER light to indicate
' reduced airflow and need for clean filters.
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