Carrier 38AK024-044 - Timer Functions; Sequence of Operation; Complete Unit Stoppage

Timer
Functions
—
(See
Fig.
14)
1. Switch A (contacts A-AI and A-A2) provides Time
Guard Control Circuit function. Start of compressor
is delayed approximately 5.5 minutes after shut-off.
The minimum time between starts of compressor is 8
minutes.
2. Switch B (contacts B-B1 and B-B2) starts compressor.
3.
Switch
D
(contacts
D-D1)
bypasses
the
low-pressure
switch
(LPS)
for
2.5
minutes
at
start-up
for
winter
start
control.
TIMER POSITION DURING
UNIT OPERATION
EMEN 150 SEC +5 5.5 MINA/——.
— KA
—-1--—-———————
COMPRESSOR
STARTS
A-A2
=
12
SEC
#2
|
—
B-BI
—{
———
—»
}e—1SEC
20.5
|
B-B2
_stia
5
SEC
+2
—EEl
———
e
—
40 SEC
$5
—
|
r_n
—
cr
D-DI
Ç]
|<
—
2-6
SEC
—
<
2-6SEC
a awOcacvvsc
D-D2
ER oe === 150 SEC #5 55 MINS/—-
Fig. 14 — Timer Cycle
(BLACK DENOTES CLOSED CONTACTS)
OMIN OR
Sequence of Operation — At start-up, the thermostat
calling for cooling and all safety devices satisfied, the control
circuit relay (CR1) closes. The indoor fan motor starts imme-
diately. With minimal demand for cooling, only ТСІ of the
thermostat is made. The timer motor starts and condenser fan
no. 1 starts. Fan no. 2 starts if high side pressure is higher than
260 psig (1793 kPa). Fan no. 3 (38AK044 only) starts if
outdoor ambient rises above 80 F. After a delay by Time
Guard? circuit of 12 seconds to approximately 8 minutes
depending on the timer position, the compressor starts and the
primary liquid line solenoid valve opens.
With only TCI calling for cooling, the capacity control
liquid line solenoid is not energized, therefore the suction
pressure is such that the compressor unloads on suction
pressure shortly after compressor start-up. The compressor
operates at either 1 or 2 steps of unloading depending on the
suction pressure which is, in turn, dependent on the
evaporator load conditions. As cooling demand increases,
TC2 of the 2-stage thermostat energizes the capacity control
liquid line solenoid causing full surface of the evaporator to
be active, tending to raise the suction pressure so that the
compressor loads.
16
A
pump-out
relay
(POR)
in
the
control
circuit
is
energized
when
thermostat
contacts
make.
A
set
of
normally
open
POR
contacts
close,
completing
a
compressor
control
circuit
which
bypasses
the
СКІ
contacts.
As
cooling
demand
is
satisfied,
the
thermostat
contacts
break,
de-
energizing
CR1.
The
LLS
valve
closes,
stopping
the
flow
of
liquid
refrigerant
to
the
evaporator
and
subsequent
suction
gas
to
the
compressor.
The
compressor
continues
to
operate
because
of
the
CRI
bypass
with
relay
TRI.
With
no
refrigerant
returning
to
the
compressor,
low
side
pumpout
takes
place
and
the
compressor
shuts
down
on
low-pressure
control.
The
compressor
does
not
restart
until
the
thermo-
stat
again
calls
for
cooling.
Complete Unit Stoppage
CAUSES — Interruption of supplied power, open discharge
gas thermostat (DGT), compressor overtemperature pro-
tection, or open high-pressure safety switch causes com-
pressor stoppage.
RESTART — The unit recycles and restarts automatically
under the Time Guard® device when power is restored.
Stoppage by DGT, HPS, or compressor circuit breaker
requires manual resetting of the control circuit. To restart
the Time Guard timer when DGT or HPS are tripped,
merely open and then close the thermostat contacts. It is
necessary to manually reset the compressor circuit breaker
at the unit.
If LPS is not closed within 2.5 minutes after compressor
starts, the compressor locks out and the outdoor fans
continue to run. It stays locked out for 5.5 minutes until the
timer motor comes back to 0 time (see Fig. 14). At 0 time, the
LPS is jumpered (winter start control). It remains jumpered
for 2.5 minutes. Because the LPS is jumpered, the com-
pressor restarts and runs for the 2.5-minute time period. At
the end of this 2.5 minutes, if the LPS has still not closed, the
compressor is again locked out. The timer motor is de-
energized and cannot restart until the LPS closes. The
outdoor fans continue to run as long as there is a call for
cooling. Automatic reset of the LPS causes the timer to
recycle so that the compressor can start.
If sufficient compressor oil pressure has not been built
within 2.5 minutes after the compressor starts, the unit is
completely de-energized until the OPS is manually reset at
the unit.
A CAUTION
If unit or circuit stoppage occurs more than once due
to any safety device, the trouble should be corrected
before any attempt to restart.