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527929-BIM-F-0911
4.
When the heating demand is satisfied, the 24 volt "W" signal
is removed and the electric heat is de-energized. The M1
contactor is de-energized when the 24 volt "Y" signal is
removed. If the fan switch on the thermostat is in the "ON"
position, the blower will continue to run at 75% of the rated
airflow. If the fan switch is in the "AUTO" position, the blower
will continue to run for a short period as determined by the
"DELAY" jumper setting on the CFM Selector board.
Please refer to Tables 14 and 15 for more information.
Defrost Operation
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 responding to a
call for defrost less than 20 minutes after the initiation 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.
A forced-defrost feature puts the system into a defrost period
every 6 hours and 4 minutes to recirculate lubricants, unless the
coil temperature is above 40 °F. All defrost timing occurs only
while the compressor is on. During the defrost mode, the
defrost control will provide a 24 volt signal from terminal "W1/
66" to the fan control terminal "W1". 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.
Demand Defrost Selection
Demand defrost jumper is factory set at position #2.
22
1
2
3
4
DEMAND
X/L
DEFROST
SELECTION
R
JUMPER
(JUMPER
C
IS SHOWN
Y
IN POSITION
#2)
O
W
W2/66
REV
VALVE
Figure 10: Demand Defrost "Curve" Selection Jumper
Heat Pump Safety Switch Operation
The unit is equipped with a safety package. The refrigeration
system will be protected against high or low refrigerant
pressure. If either of these safety switches opens, the unit will
be shut off for the 5 minute anti-short cycle time. Once this has
expired, a six hour elapsed run timer begins. If a second
opening of a safety switch occurs during this six hour period,
the compressor will be locked out. Resetting the lockout
function is accomplished by:
1.
Removing power from the control's thermostat 1st stage
(Y) input for a time not to exceed 5 seconds (ON-OFF-ON).
2.
Removing power from "R" for more than 2 seconds.
3.
Shorting the "TEST" pins together for more than 2 seconds.
Electric Heat Limit Switch Operation
The limit switch responds to over-temperature conditions in the
air duct. Opening the device results in dropping power to the
relays. The control logic will also respond by turning off the
relays. After four limit cycle trips the unit goes into a 1 hour soft
lockout period. If the control "sees" another limit cycle during
this period, the unit will go into a hard lockout condition. Once in
a hard lockout state, the fan is locked on and the heaters are
disabled. Only a power cycle will clear this state.
During the soft lockout period, the fan responds to thermostat
input but the heaters are enabled. This is to sense a failed
heater relay. The limit cycle count is reset at the start of a heat
request. If the limit remains open for period of 80 seconds or
more, the control is immediately put into a hard lockout
condition. Only a power cycle will clear this state.
TEST
PRESSURE
M
SWITCH
Johnson Controls Unitary Products
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