5168273-YIM-A-1115
38
Johnson Controls Unitary Products
available). For the 18 kW heater 18 kW will be energized, for
the 36 kW heater 18 kW will be energized, for the 54 kW heater
18 kW will be energized, and for 72 kW heater 36 kW will be
energized. In the event that all compressors are locked out by
the UCB, the total available kW of electric heat will be energized
on a call for “W2”. Take note that the MV terminal on the UCB is
constantly monitored while there is a demand for heat. If the
UCB does not see 24vac at terminal MV after six minutes, it
initiates an LCD display alarm, indicating a heating problem.
Without Electric Heat
When the thermostat calls for heating, the low voltage control
circuit is completed between “R” and “W1”. This 24vac signal is
passed through the UCB to the RW1 Relay and the MV terminal
on the UCB. Contacts RW1-1 open, assuring the reversing
valve cannot be energized, except during defrost. Contacts
RW1-2 close. If its ASCD timer is satisfied the UCB will
energize compressor #1 contactor M1. After a two second
delay, it then energizes compressor #2 contactor M2.
Therefore, on a call for heat from W1, both sets of compressors
are always energized, unless one or the other is locked out by
the UCB. Also on the call for heat, the UCB energizes the M4
and M6 contactor, which brings on the condenser fans.
Take note that the MV terminal on the UCB is constantly
monitored while there is a demand for heat. If the UCB does not
see 24vac at terminal MV after six minutes, an LCD display
alarm will indicate a heating issue.
Defrost Initiation
Defrost control implements a temperature differential, demand
defrost algorithm. The heat pump is allowed to operate in the
heating mode until the combination of outdoor ambient
temperature and outdoor coil temperature indicate that
defrosting is necessary. When the coil temperature is
maintained below the initiate point for a given 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.
For defrost, the UCB will signal the energizing of the reversing
valve and de-energizing the systems condenser fan
motor(s).The unit's optional electric first-stage heater is also
energized via a 24-volt VAC output terminal labeled "H2".
Defrost Termination
The UCB terminates the defrost mode when either of the
following two conditions are met;
1.
The outdoor coil temperature sensor reaches 50°F, or
2.
The maximum allowable defrost run time of 8 minutes.
Interval between Defrosts
A timed inhibit feature prevents the system from responding to
a call for defrost less than 40 minutes after the initiation of the
previous defrost. After this inhibit time has expired, temperature
conditions must call for defrost continuously for 4- 1/2 minutes
before another defrost cycle is initiated. A temperature inhibit
feature prohibits defrost if the coil temperature is above 40°F.
All defrost timing occurs only while the compressor is on.
Forced Defrost
A forced-defrost feature puts the system into a defrost cycle
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.
For trouble shooting purposes, the defrost cycle can be
manually initiated by selecting "Test Defrost" in the UCB menu.
Electric Heat Operation Errors
Temperature Limit
If the UCB senses zero volts from the high temperature limit,
the indoor blower motor is immediately energized.
This limit is monitored regardless of unit operation status, i.e.
the limit is monitored at all times.
If the temperature limit opens three times within one hour, it will
lock-on the indoor blower motor.
Safety Controls
The UCB monitors the temperature limit switch of electric heat
units.
Temperature Limit Switch (TLS 1, 2)
This control is located inside the heater compartment and is set
to open at the temperature indicated in the Limit Control Setting
Table 17. It resets automatically. The limit switch operates
when a high temperature condition, caused by inadequate
supply air flow occurs, thus shutting down the heater and
energizing the blower.
Table 17: Limit Control Setting
VOLTAGE
HEATER
Limit Switch Opens, ºF
kW
TLS1
TLS2
208/230
18
140
-
36
140
140
54
140
120
72
140
120
460
18
120
-
36
120
120
54
120
110
72
130
110
575
18
120
-
36
120
120
54
120
120
72
120
120
