Carrier 50PQ - Manual (Page 13)

outdoor ambient reaches the outdoor thermostat set point, the
heating element contactor is energized when thermostat
second stage heating contacts close, bringing on additional
electrical resistance heat
50RQ,PQ008/010 - On the 50RQ,PQ008 and 010, 2-
compressor units, when thermostat second stage heating
contacts close, compressor contactor no 2 energizes and
compressor no 2 is brought on Units have a built-in electric
resistance heat lock-out thru the defrost thermostat Above
40 F (approximate) outdoor temperature, electric resistance
heat is locked out and second stage heat is from compressor
no 2 Below 40 F (approximate) ambient, when thermostat
first stage heating contacts close, compressor contacts no 1
and no. 2 energize sequentially thru a time delay and both
compressors (no 1 and no 2) are brought on to satisfy heating
requirements
On a further drop in room temperature (outdoor ambient
below 40 F), thermostat second stage heating contacts close,
energizing electric resistance heat contactor and second stage
heat operates Electric heaters with 2 or more contactors can
have outdoor thermostats wired into the control circuit for
additional staging
Automatic changeover — When the system selection switch is
set at AUTO , unit automatically changes from heat operation
to cooling operation when the temperature of the conditioned
space rises to the cooling lever setting When the temperature
of the conditioned space fails to the heating lever setting, unit
automatically changes from cooling to heating operation (with
a 3 F deadband in between)
Continuous air circulation — Unit power on System control
set at OFF, fan switch set at ON Indoor fan contactor is
energized thru the thermostat switch and the indoor fan runs
continuously When controls are set at HEAT, COOL, or
AUTO , operation is as above and indoor fan runs
continuously.
Defrost cycle
50RQ/PQ006 — The defrost thermostat on the outdoor coil
activates a defrost timer which energizes electric resistance
heaters and de-energizes the reversing valve relay and the
outdoor fan motor When the defrost thermostat is satisfied or
when 10 minutes have elapsed, the reversing valve solenoid
energizes and electric heaters de-energize The defrost timer
prevents defrost again for 90 minutes
50RQ,PQ008/010 — Operation is same as above, except both
reversing valve relays de-energize or energize simultaneously
off the defrost timer and thermostat
On the 008 and 010 units, the defrost thermostat in
conjunction with a time delay relay prevent electric heat
operation above an ambient temperature of approximately
40 F (depends on coil frost conditions) If defrost thermostat
closes, the time delay relay energizes and pulls in compressor
contactor no 2 Both compressors now operate off of W1 and
W2 controls electric heat
Economizer operation
Unit power on, thermostat set at COOL or AUTO , outside
temperature
below setting of outside air changeover
thermostat
Upon a rise in room temperature, cooling contact no 1 in
the thermostat closes Indoor fan motor starts and outside air
damper modulates to maintain mixture of outside air and
return air at present temperature Cooling is provided with
outside air Mechanical cooling is locked out
At temperatures above outdoor air changeover thermostat
setting, outdoor air damper moves to VENT position whenever
fan is running, and cooling operation is as described for base
unit When heat is energized, outdoor air damper moves to
VENT position Outdoor air damper closes when fan is not
operating
Signal-LOC^'^protection with "LK-OUT" light
If unit operation is interrupted by an open high-pressure
switch, low-pressure switch, indoor coil freezestat, or by the
compressor internal line break device (overcurrent or over­
temperature), and the compressor is calling for either cooling
or heating, Signal-LOC simultaneously locks out the unit and
lights a warning light (LK-OUT) on the thermostat Unit is
restarted by manually turning room thermostat OFF and then
ON If any of the protective devices open again, unit continues
to lock out until corrective action is taken
Accessories
Emergency heat
If the compressor is inoperative due to a tripped safety device
(high pressure, low pressure, indoor coil freezestat, overcurrent
or over-temperature), Signal-LOC locks out the compressor and
lights the warning light (LK-OUT) on the room thermostat
When the switch is on, the thermostat is moved to the EM.
HT. position, the compressor circuit and the outdoor thermo­
stats are bypassed and the second stage of the thermostat
energizes the indoor fan and the electric resistance heaters.
Time Guard®
The accessory Time Guard control circuit provides a 5-minute
delay of compressor restart after the desired space temperature
has been attained and the room thermostat has shutdown the
compressor Assuming that the compressor has been off for at
least 5 minutes due to room thermostat action, the Time
Guard control sequence is as follows
With the fan selector switch at AUTO , a call for cooling
from the room thermostat causes the indoor air fan to start
immediately, the compressor and outdoor air fan start 15
seconds later When the room thermostat is satisfied, the
compressor shuts off The Time Guard timer motor then runs
for 4 minutes and 45 seconds, at which point its internal
switches reset so the normal sequence can begin again
The base unit contains as standard equipment, a factory-
installed Signal-LOC compressor protection device If the
overload protector causes the compressor to shut off, the
compressor remains locked out until the control circuit is
manually reset Reset manually by moving the system selector
lever on the room thermostat to OFF momentarily and then
return it to the cooling position After the standard 5-minute
Time Guard delay, the compressor can restart
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