Unit installation

6
The H Series units use an integrated defrost control to manage the
following control functions of the system:
1. Off and on functions of the outdoor fan during the defrost and
heating mode.
2. Off and on functions of the reversing valve during the defrost
and heating mode.
3. Off and on functions of the auxiliary heat relays during the
defrost mode.
The control is a time-and-temperature type with selectable defrost
time intervals of 30, 60 and 80 minutes. Control circuit voltage at the
control is 24 volts input and output. The outdoor fan relay is SPNC
(single pole normally closed) and controls the fan motor.
BASIC SEQUENCE OF OPERATION
COOLING MODE
Low-voltage thermostat terminal R is connected to Y and O, at the
unit low-voltage terminal board.
The system reversing valve is powered during the cooling mode.
Power is supplied to the reversing valve solenoid through the low-
voltage O terminal. The low-voltage Y terminal to the control will
energize the contactor latch coil (causing the contactor to energize
the compressor). The low-voltage Y terminal to the control will also
energize the control's timer. During the cooling mode, the defrost
thermostat is open (coil temperature is above 30°F) and will not
allow the time to be accumulated to initiate the defrost mode. The
outdoor fan is wired through the N/C points of the control’s relay and
the N/O points of the contactor. The fan motor will be energized
whenever the contactor is energized (except during defrost).
HEATING MODE
Low-voltage terminal R is connected to Y and G, at the unit low-
voltage terminal board.
The system reversing valve is not powered during the heating mode.
With the thermostat system switch turned to heat, the low-voltage O
terminal is now disconnected, turning the reversing valve solenoid
off (switching the reversing valve to the heat position). The Y
terminal will energize the contactor and outdoor fan and the G
terminal will energize the indoor blower.
DEFROST MODE
To prevent heavy ice build-up on the coil during the heating mode,
as the outdoor coil temperature falls below 30°F ± 5°F, an outdoor
defrost thermostat closes. (This thermostat is located on a coil tube.)
When the thermostat closes, the timer on the defrost control starts
accumulating the compressor run time. After the selected time (30,
60, or 80 minutes) has been accumulated, the controller will start the
defrost cycle regardless of the outside temperature. During the
defrost cycle, the system is switched back into the cooling mode by
the control energizing the reversing valve solenoid. The N/C pole of
the control fan relay is opened, turning off the outdoor fan to allow
the outdoor coil to be warmed (defrosted) faster. The defrost control
energizes the indoor auxiliary heat relays through the W2 terminal to
temper the indoor supply air. This terminal should be connected to
W2 (second-stage heat) on the thermostat.
After the defrost thermostat reaches 65°F ± 5°F, the defrost cycle
will end. The control has a defrost default at 10 minutes that will not
allow the defrost to continue longer than 10 minutes.
DEFROST TIME SELECTION
The defrost control has three selectable time intervals: 30, 60 and
80 minutes. The timing is factory set at 60 minutes. This timing has
been determined by testing to provide the best operating efficiency.
In areas where the humidity is lower than normal, the timer may be
set to a higher time (80 minutes). To change the time, move the
timer jumper to the post marked 30 for 30 minutes, 60 for 60
minutes, or 80 for 80 minutes.
DEFROST TEST POST
The defrost control has test posts to speed up the defrost time
setting by a factor of 256.
If you want to initiate a defrost without waiting for the time to
accumulate, you can jumper the two test pins (marked test). If the
coil temperature is above 30°F you will need to jumper the DFT
(defrost thermostat) terminals to simulate a closed thermostat. The
defrost cycle should occur in 7 seconds for a 30-minute setting, 14
seconds for a 60-minute setting, and 17 seconds for an 80-minute
setting. If the jumper is removed immediately when the defrost cycle
starts, the cycle will end if the defrost thermostat is opened (coil
above 65°F). If the test pins remain jumped, and the defrost
thermostat is closed, the defrost will end in 2.3 seconds, which is the
10-minute default.
DURING THE ABOVE TEST, DO NOT CONTACT OR SHORT
ANY OTHER PIN. THIS MAY DAMAGE THE CONTROL.
FIELD CHARGING
Compared to a cooling-only unit, a heat pump is difficult to field
charge correctly without the use of charging scales. It is
recommended the charge be weighed in with an accurate charging
scale. The correct charge weight can be found on the unit name
plate.
H Series units are equipped with a high pressure switch. This switch
is wired through a lockout relay to lock out the system if the high side
pressure exceeds 425 psi. If the system is locked out by the
pressure switch, it can be reset by cycling the indoor thermostat off
and back on. The high side pressure MUST be below 300 psi before
the system can be reset.
M. DEFROST CONTROL
N. HIGH PRESSURE LOCK OUT