Carrier 38AK024-044 - Manual (Page 19)

Timer Functions — (See Fig. 14)
1 .
Switch A (contacts A-Al 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.
Switch B (contacts B-Bl and B-B2) starts compressor.
Switch D (contacts D-Dl) bypasses the low-pressure
switch (LPS) for 2.5 minutes at start-up for winter start
control.
(BLACK DENOTES CLOSED CONTACTS) TIMER POSITION DURING
UNIT OPERATION^
OMIN OR
J.P ---------------- 150 SEC ±5 ----------------------
_ A-AI ---------
h-—COMPRESSOR STARTS
A-AZ*^
U— 12 SEC +2 1
® -¡-M f------------------1 SEC io.5 1
------ 5 SEC ±2 1
— E-El -------
----- 40 SEC i5 --------- M 1
— D-DI
'-H I- -2-6SEC 2-6 SEC
D-D2
150 SEC ±5 -5.5 MIN^A--
Fig. 14 — Timer Cycle
Sequence of Operation — At start-up, the thermostat
calling for cooling and all safety devices satisfied, the control
circuit relay ( C R l ) closes. The indoor fan motor starts imme­
diately. With minimal demand for cooling, only TCI 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.
A pump-out relay (FOR) in the control circuit is
energized when thermostat contacts make. A set of normally
open FOR contacts close, completing a compressor control
circuit which bypasses the CRl contacts. As cooling
demand is satisfied, the thermostat contacts break, de­
energizing C R l . The LLS valve eloses, stopping the flo\v of
liquid refrigerant to the evaporator and subsequent suction
gas to the compressor. The compressor continues to operate
because of the CRl bypass with relay T R l . With no
refrigerant returning to the compressor, low side pumpout
takes place and the compressor shuts down on lowrpressure
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 switeh eauses com­
pressor stoppage.
RESTART — The unit recycles and restarts automatically
under the Time Guard® device when power is restored.
Stoppage by DGT, HFS, or compressor circuit breaker
requires manual resetting of the control circuit. To restart
the Time Guard timer when DGT or HFS are tripped,
merely open and then close the thermostat contacts. It is
necessary to manually reset the compressor circuit breaker
at the unit.
If LFS 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
LFS is jumpered (winter start control). It remains jumpered
for 2.5 minutes. Because the LFS 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 LFS has still not closed, the
compressor is again locked out. The timer motor is de­
energized and cannot restart until the LFS closes. The
outdoor fans continue to run as long as there is a call for
cooling. Automatic reset of the LFS 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 OFS 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.
16