Carrier 38AH044-134 - Manual (Page 47)

Fig. 45 — Accumulator and Fusible Plug
Timer Functions — (See Timer Cycle, Fig. 47.) Each
refrigeration circuit is controlled by an independent timer
which allows for the independent operation of each refrig­
eration circuit.
NOTE: Unit 38AH044-084 optional single-circuit units have
one timer which controls the lead compressor. Lag compres­
sor is controlled by CCPS (capacity control pressure switch).
SWITCH A — The timer is energized through contacts A-Al
or A-A2. This establishes the Time Guard® function which
prevents compressor short-cycling. Start of compressor is de-
i layed approximately 5.5 minutes after shutdown.
^' SWITCH B — The compressor is initially energized through
contacts B-Bl.
SWITCH D — Contacts D-Dl provide a 2*/2-minute bypass
of the low-pressure switch at start-up for winter-start con­
trol. On 38AH044-084 optional single-circuit units, contacts
D-D2 control start-up of compressor A2.
SWITCH E — Contacts E-EI provide a 40-second bypass
of the oil pressure switch at start-up. If oil pressure does not
build to the required minimum pressure in 40 seconds, the
compressor shuts down and the control circuit locks out.
On 38AH044-084 dual-circuit and 38AH094,104 units, lag
circuit B start-up is delayed 60 seconds after a call for cool­
ing is made to the circuit. This prevents compressor(s) in
both lead and lag circuits from starting at the same time.
Control Circuit Reset — The control circuit locks out
if the unit shuts down because of low oil pressure, high dis­
charge gas temperature (DGT), or excessive high-side pres­
sure. To reset the control circuit, open and close the fan cir­
cuit breaker (FCB). This resets the timer, and the unit restarts
under Time Guard control. At start-up, if the low-pressure
switch (EPS) does not close after 2'/2 minutes, the unit shuts
down. When the pressure builds enough for the EPS to cut
in, the control circuit is energized automatically and start-up
proceeds under Time Guard control.
TO PREVENT REFRIGERANT LEAKAGE)
Fig. 46 — Pressure-Actuated Capacity Control Valve
CONTROL
Sequence of Operation — Units are controlled with
electromechanical components. Each refrigeration circuit
(except 38AH044-084 optional single-circuit units) is oper­
ated by an independent timer which controls the operation
sequence of each circuit.
On a call for cooling, first stage cooling thermostat TCI
closes. Condenser fans and timer (TM) are energized. After
approximately 7 seconds, timer contacts E-El close. Ap­
proximately 12 seconds after TCI closes, normally-open timer
contacts B-B1 close for 1 second. This energizes compres­
sor A1 contacts CAl and starts the compressor. At the same
time, solenoid drop relays (SDRs) and liquid line solenoid
valve no. 1 (EES-A for 38AH044-084 dual-circuit units;
EES-Al for all other units) open, and timer relay no. 1 (TR2)
is energized. Normally open TR2 contacts close, completing
a circuit around B-Bl and through compressor A1 contac­
tors to maintain compressor operation when B-Bl contacts
open. Contacts E-El remain closed for approximately 40 sec­
onds to bypass the oil pressure switch (OPS). If oil pressure
is insufScient when contacts E-El open, the compressor stops,
the timer cycles off, and the control circuit locks out. At start­
up, timer contacts D-Dl are closed, bypassing low-pressure
relay contacts EPR-A for 21/2 minutes. This provides a win­
ter start-up feature.
Approximately 2V2 minutes after TCI closes, timer con­
tacts D-Dl open and D-D2 close. If pressure is insufficient
to close the low-pressure switch, the low-pressure switch re­
lay is open, the compressor shuts down, and the Time Guard
control is initiated. (Time Guard control prevents compres­
sor from restarting for 5 minutes after the demand for cool­
ing is satisfied.)
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