66396-YIM-C-1004
30
Unitary Products Group
(DC)
. If its ASCD timer is satisfied the UCB will ener-
gize compressor #1 and #2 contactor M1. After a two
second delay, it then energizes compressor #3 and #4
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 DC energizes the M4 and M5 contac-
tor, which brings on both condenser fans.
Take note that the MV terminal on the UCB is con-
stantly monitored while there is a demand for heat. If
the UCB does not see 24vac at terminal MV after six
minutes, it initiates a fault code 9, indicating a heating
problem.
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:
1.
The DC must first satisfy its accumulated minimum
run time. This is factory set at 60 minutes, but is
field adjustable to 30, 60 or 90 minutes.
2.
Either of the two defrost thermostats (DF1 or DF2)
must be closed. These normally open thermostats
are mounted on the respective liquid lines and are
set to close at -1°C (31°F).
If neither defrost thermostat is closed at the completion
of it’s minimum accumulated run time cycle, the DC ini-
tiates another run time cycle, which it must complete
before it looks at the position of the defrost thermo-
stats. This action is repeated until, at the completion of
a run time cycle, one of the defrost thermostats is
found to be closed and the DC enters defrost mode.
When the DC enters the defrost mode, it’s on-board
defrost relay is powered. This energizes both reversing
valves, de-energizes both condenser fan motors and
energizes the unit’s optional electric heater. The DC
remains in defrost mode until either of the following two
conditions is met:
1.
Both of the liquid line thermostats are open. Each
is set to open at 13°C (55°F).
2.
The maximum defrost run time of 10 minutes is met.
The DC also contains a set of test pins
.
Placing a
jumper across these pins will result in the following
actions:
•
If the ASCD timer is active, it is now by-passed,
allowing the compressor to run.
•
If the DC is in a lockout condition, the lockout is
reset.
•
If the compressor is running, the DC is forced into
defrost mode. The control will remain in defrost
mode for as long as the jumper is in place. When
the jumper is removed, the control will terminate
the defrost mode in the normal manor as described
above.
NOTE:
The DC has two flashing codes which are only
initiated if the two pressure switch terminals
are open. As used in this unit, there is a
jumper across the pressure switch terminals.
Therefore the field should never experience a
DC lockout mode unless that jumper is
removed or broken.
HEATING 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 sta-
tus, 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 and a flash
code is initiated (See Table 21).
SAFETY CONTROLS
The unit control board monitors the temperature limit
switch of electric heat units.
The control circuit includes the following safety controls:
1.
Temperature Limit Switch (TLS 1, 2).
This control is located inside the heater compart-
ment and is set to open at the temperature indi-
cated in the Limit Control Setting Table 19. 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.
2.
Temperature Limit Switch (TLS 3, 4, 5 and 6).
This control is located inside the heater compart-
ment and is set to open at the temperature indicated
in the Limit Control Setting Table 19. It is a manual
reset limit. These limit switches will de-energize the
heaters should the primary limit fail to open or the
contactors fail to open in a failure mode.
