Reset; Heating Sequence Of Operations; With Or Without Electric Heat; Defrost Mode (3 Thru 5 Ton) - York sunline 2000 Installation Manual

RESET

Remove the call for cooling, by raising thermostat set-
ting higher than the conditioned space temperature.
This resets any pressure or freezestat flash codes.

HEATING SEQUENCE OF OPERATIONS

WITH OR WITHOUT ELECTRIC HEAT

When the thermostat calls for the first stage of heating,
the low voltage control circuit is completed between "R"
and "W1". The 24vac signal is passed through the UCB
to the "Y" contact on the Defrost Control (DC) assuring
the reversing valve cannot be energized, except during
defrost. If the ASCD timer is satisfied the UCB will
energize compressor contactor M1.
If the compressor alone cannot satisfy the heating
requirements, a second stage call from the thermostat
completes the circuit between "R" and "W2". This
24vac signal is passed through the UCB to the electric
heat section (if available). The total available kW of
electric heat will be energized on a call for "W2".

DEFROST MODE (3 THRU 5 TON)

The demand defrost control implements a temperature
differential ("delta-T") demand defrost algorithm. The
heat pump is allowed to operate in the heating mode
until the combination of outdoor ambient and outdoor
coil temperatures indicate that defrosting is necessary.
When coil temperature is below the initiate point for the
ambient temperature continuously for 4-1/2 minutes,
the heat pump is put into a defrost cycle. This 4-1/2
minute timer eliminates unnecessary defrost cycles
caused by refrigeration surges such as those that
occur at the start of a heating cycle.
A timed inhibit feature prevents the system from respond-
ing to a call for defrost less than 20 minutes after the initi-
ation of the previous defrost. After the 20 minute inhibit
time has expired, temperature conditions must call for
defrost continuously for 4-1/2 minutes before a defrost
cycle is initiated. A temperature inhibit feature prohibits
defrost if the coil temperature is above 40°F.
FORCED DEFROST
A forced-defrost feature puts the system into a
defrost period every 6 hours and 4 minutes to recir-
culate lubricants, unless the coil temperature is
above 40°F. All defrost timing occurs only while the
compressor is on.
Johnson Controls Unitary Products
During the defrost mode, the defrost control will provide
a 24 volt signal from terminal "W1/66" to the fan control
terminal "W2". This signal will energize electric heat
stage 1, if the unit is so equipped.
For trouble shooting purposes, the defrost cycle can be
manually initiated by shorting the "TEST" pins together
for 5 seconds. Defrost will terminate normally during
the "TEST" mode.

DEFROST MODE (6 TON)

As mentioned earlier, the defrost control (DC) utilizes a
time/temperature defrost scheme. The following two
conditions must be met before the DC will enter a
defrost mode:
The defrost thermostat (SD) must be closed. This nor-
mally open thermostat is mounted on the liquid line and
is set to close at 28 ± 4°F.
Once the defrost thermostat closes, the defrost control
starts a run timer that must be satisfied before defrost
can begin. This is accumulated compressor run time.
The selection pin is factory set at 60 minutes, but is
field adjustable to 30, 60 or 90 minutes.
When the DC enters the defrost mode, it's on-board
defrost relay is powered. This energizes the reversing
valve, de-energizes the condenser fan motor and ener-
gizes the unit's optional electric heater. The DC
remains in defrost mode until either of the following two
conditions is met:
1. The liquid line thermostat is open. It is set to open
at 55 ± 4°F.
2. The maximum defrost run time of 10 minutes is met.
FORCED DEFROST
The processor on the defrost board is only energized
when the defrost sensor (DS) is closed.
To create a forced defrost:
1. The DS must either be closed or a jumper must
be placed across the DFS terminals on the
board.
2. Place a jumper across the test pin terminals on the
board.
Depending on the selected defrost minimum run
time of 30, 60 or 90 minutes, the board will go into
defrost in 7.5, 15 or 22.5 seconds.
The DC will remain in defrost until the jumpers
across the DS and the test pin terminals are
removed.
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