Product data

27
Defrost (50TFQ004-007 and 50HJQ004-007) —
As frost builds up on the outdoor coil, the coil temperature
drops below 28 F. When this outdoor-coil temperature
drop is sensed by the defrost thermostat (DFT) and the de-
frost timer is at the end of a timed period (adjustable at 30,
50, or 90 minutes), the unit operates in a defrost cycle
controlled by the defrost timer and thermostat. During this
cycle, the reversing valve solenoid (RVS) is energized and
the outdoor fan shuts off. The electric heaters (if installed)
will be energized.
The unit continues to defrost until the coil temperature
as measured by DFT reaches 65 F, or the duration of de-
frost cycle completes a 10-minute period.
At the end of the defrost cycle, the electric heaters (if in-
stalled) and the reversing valve will be deenergized, and the
outdoor-fan motor will be energized. The unit will now op-
erate in the Heating mode.
If the thermostat is satisfied during a defrost cycle, the
unit will continue in the Defrost mode until the time or tem-
perature constraints are satisfied.
Defrost (50TFQ008-012 and 50HJQ008,012) —
When the temperature of the outdoor coil drops below 28 F
as sensed by the defrost thermostat (DFT2) and the defrost
timer is at the end of a timed period (adjustable at 30, 50,
or 90 minutes), reversing valve solenoids (RVS1 and RVS2)
are energized and the OFC is deenergized. This switches
the position of the reversing valves and shuts off the out-
door fan. The electric heaters (if installed) will be energized.
The unit continues to defrost until the coil temperature
as measured by DFT2 reaches 65 F, or the duration of de-
frost cycle completes a 10-minute period.
During the Defrost mode, if circuit 1 defrosts first, RVS1
will oscillate between Heating and Cooling modes until the
Defrost mode is complete.
At the end of the defrost cycle, the electric heaters (if in-
stalled) will be deenergized; the reversing valves switch and
the outdoor-fan motor will be energized. The unit will now
operate in the Heating mode.
If the space thermostat is satisfied during a defrost cycle,
the unit will continue in the Defrost mode until the time or
temperature constraints are satisfied.
Sequence of operation — 50HJQ014,016
Cooling, units without economizer — With unit main
power on, set thermostat to COOL position and desired
room temperature. Set fan switch at AUTO. (on demand)
or ON (continuous) position.
On a rise in room temperature, cooling contactor no. 1
in the thermostat closes. The indoor and outdoor fan mo-
tors start. If the 5-minute compressor time-delay (CTD) on
the defrost board (DB) is satisfied, then compressor no. 1
(50HJQ016) or unloaded compressor (50HJQ014) con-
tactor is energized and compressor will start. Compressor
cycles on demand of the thermostat to satisfy room condi-
tions. Each time the cooling contactor no. 1 opens, the
CTD starts the 5-minute delay.
On 50HJQ016 units, with an additional rise in room
temperature, cooling contactor no. 2 in the thermostat clos-
es, energizing compressor contactor no. 2. Compressor
no. 2 starts and cycles on demand of the thermostat to sat-
isfy the occupied space demands.
On 50HJQ014 units, compressor runs fully loaded on a
call for second-stage cooling.
Cooling, units with economizer — Upon a call for
cooling, when outdoor ambient temperature is above the
temperature control setting, the indoor and outdoor fans
and compressor(s) energize. The economizer damper
moves to vent position.
Upon a first-stage call for cooling, when outdoor ambi-
ent temperature is below the temperature control setting,
the indoor fan starts and economizer damper modulates to
maintain mixed-air temperature. The compressor(s) re-
mains off.
Upon a second-stage call for cooling, compressor no. 1
(50HJQ016) or loaded compressor (50HJQ014) is ener-
gized and mechanical cooling is integrated with economiz-
er cooling. Compressor no. 2 (50HJQ016) is locked out. If
the air temperature is below 50 F, a cooling lockout switch
prevents the compressor(s) from running.
When supply-air temperature drops below a fixed set
point, the economizer damper modulates to maintain the
temperature at the fixed set point.
A freeze protection thermostat (FPT) is located on the
indoor coil. It detects frost build-up and turns off the com-
pressor(s), allowing the coil to clear. Once frost has melted,
the compressor can be reenergized.
Heating, units without economizer — With unit main
power on, set thermostat at HEAT position and desired
room temperature. Set fan switch at AUTO. (on demand)
or ON (continuous) position.
On a drop in room temperature, heating contactor no. 1
in the thermostat closes, energizing heat relay (HR), revers-
ing valve relay (RVR), reversing valve solenoids (RVS1 and
RVS2) and compressor no. 2 contactor. Compressor (size
014) or compressor no. 2 (size 016) and indoor and out-
door fan motors start. If the 5-minute CTD on the DB is
satisfied, then compressor no. 1 contactor is energized and
compressor no. 1 will start.
On units equipped with electric heat, when additional
heat is needed, heating contactor no. 2 in the thermostat
closes, energizing W2.
Heating, units with economizer — With unit main
power on, set thermostat at HEAT position and desired
room temperature. Set fan switch at AUTO. (on demand)
or ON (continuous) position.
On a drop in room temperature, heating contactor no. 1
in the thermostat closes, energizing heat relay (HR), revers-
ing valve relay (RVR), reversing valve solenoids (RVS1 and
RVS2) and compressor no. 2 contactor. Compressor no. 2
(016) and indoor and outdoor fan motors (014,016) start.
If the 5-minute CTD on the DB is satisfied, then compres-
sor (014) or compressor no. 1 (016) contactor is energized
and compressor (014) or compressor no. 1 (016) will start.
The outdoor-air damper stays at vent position while the in-
door fan is operating.