Carrier 40RR024 - Manual (Page 6)

When the thermostat calls for first-stage cooling (TCI
closed), the indoor-fan motor starts immediately. Compres­
sor no. 1 and outdoor fan no. 1 start after 3 seconds and
before 5 minutes depending on the length of time system is
off after thermostat was previously satisfied. (This time pro­
cess is effective because of the 5-minute Time Guard® II
circuit.) The reversing valve solenoid (RVSl) deenergizes,
causing the reversing valve to shift to the cooling position.
The crankcase heater is off when the compressor is operat­
ing. The liquid line solenoid valve in circuit no. 1 opens,
allowing refrigerant to flow.
When the thermostat calls for second-stage cooling (TC2
closed), compressor no. 2 and outdoor fan no. 2 start. The
reversing valve solenoid (RVS2) is deenergized, causing the
reversing valve to shift to the cooling position. The liquid
line solenoid in circuit no. 2 opens, allowing refrigerant
flow in circuit no. 2.
When the second stage of thermostat is satisfied (TC2),
compressor no. 2 shuts off and outdoor-fan motor no. 2
shuts off. When the first stage of thermostat is satisfied,
compressor no. 1, outdoor fan no. 1, and indoor fan shut
off. The liquid line solenoid valve closes in each refriger­
ation circuit when the corresponding compressor shuts off.
The reversing valves do not shift but remain in the cooling
position until there is a call for heating.
The unit is equipped with a no-dump reversing valve logic.
When the unit is in the cooling mode, the reversing valve
remains in cooling mode position until the thermostat calls
for heating Conversely, when the unit is in the heating mode,
the reversing valve remains in heating mode position until
the thermostat calls for cooling.
NOTE: If a malfunction occurs, causing the high-pressure
switch (HPS), compressor overtemperature (COTP) safety,
or loss-of-charge switch (LCS) to open, the compressor in
the affected circuit is locked out by a Cycle-LOC™ circuit.
This causes the Signal-LOC™ warning light to come on at
the thermostat subbase. The remaining refrigeration circuit
continues to operate. The RVS remains deenergized on the
inactive circuit so reversing valve does not shift. These safe­
ties are reset by adjusting the thermostat up to open TCI
and TC2, or by momentarily switching thermostat subbase
to OFF position. If the compressor oil pressure is lost, or if
oil pressure fails to build on start-up on either refrigeration
circuit, an oil-pressure safety switch shuts off the affected
compressor. The switch must be reset manually at the unit.
IMPORTANT: Do not reset more than once! If oil
pressure switch trips, determine cause and correct. Do
not bypass oil pressure safety switch.
The crankcase heaters are in an electrical lockout circuit.
If a crankcase heater is defective, the compressor is locked
off. The compressor remains off until the crankcase heater
is replaced. This lockout circuit cannot be reset by adjust­
ing the thermostat.
Heating
NOTE: When power is supplied to a system that is off, the
crankcase heaters are energized. The reversing valve may
or may not be energized depending on mode of operation
(heating or cooling) when the thermostat was previously
satisfied.
The following heating operating sequence has both heat
pump circuits connected to a single, 2-circuit fan coil. The
system is controlled by a single 2-stage heat/2-stage cool
thermostat.
Copyright 1992 Carrier Corporation
When the thermostat calls for heating (THl closed), the
indoor-fan motor starts. Compressor no. 1 and outdoor fan
no. 1 start after 3 seconds and before 5 minutes depending
on the length of time system is off after thermostat is sat­
isfied. (The time process is effective because of the 5-minute
Time Guard II circuit.) The liquid line solenoid valve for
circuit no. 1 opens when compressor no. 1 operates and
closes when compressor no. 1 is off. The reversing valve in
circuit no. 1 shifts (RVSl energized) for heating operation.
When the thermostat for second stage of heating closes (TH2),
compressor no. 2 and outdoor fan no. 2 start, liquid line
solenoid no. 2 opens, and reversing valve in circuit no. 2
shifts (RVS2 energized).
When thermostat TH2 is satisfied, compressor no. 2 shuts
off, liquid line solenoid no. 2 closes, and outdoor fan no. 2
shuts off. When thermostat THl is satisfied, compressor
no. 1, outdoor-fan motor no. 1, and indoor-fan motor shut
off, and liquid line solenoid valve no. 1 closes. The revers­
ing valves remain in the heating position until there is a call
for cooling.
If either circuit is locked out, the electric heater (if in­
stalled) will be energized as long as the thermostat contin­
ues to call for heat.
Defrost — An outdoor coil temperature of 28 F (-2 C)
triggers operation of the defrost timer logic on either circuit
so that defrost becomes automatic with a time sequence,
adjustable at 30, 50, or 90 minutes. As long as the outdoor
coil temperature remains below 28 F (-2 C), defrost occurs
every 30, 50, or 90 minutes on that circuit depending on
the time selected. When defrost is initiated, the heat pump
reverts to a modified cooling mode of operation (the out­
door fan for the affected circuit shuts off). This modified
cooling mode utilizes heat rejection from the refrigerant to
melt any ice or frost on the outdoor coil. When defrost is
initiated on circuit no. 1, RVSl is energized and shifts the
reversing valve on this circuit. If defrost is not called for on
circuit no. 2, this circuit continues to run in heating until
enough frost or ice is built up on the coil to initiate defrost.
Circuits no. 1 and no. 2 reversing valves shift indepen­
dently of one another, because the coil temperatures are sensed
independently. (TDFl [thermistor, defrost 1] is attached to
circuit no. 1, and TDF2 is attached to circuit no. 2.)
Defrost for circuits no. 1 and no. 2 is also terminated in­
dependently. When temperature of either outdoor coil reaches
68 F (20 C) or length of defrost time exceeds 10 minutes,
the reversing valve on that circuit shifts back to heating mode
of operation and the outdoor fan on that circuit restarts.
NOTE: If a malfunction occurs, causing the HPS, COTP,
or LCS to open, the compressor in the affected circuit is
locked out by a Cycle-LOC^“ circuit. This causes a Signal-
LOC™ warning light to come on at the subbase. The re­
maining refrigeration circuit continues to operate. The RVS
remains energized so reversing valve does not shift. Signal-
LOC device resets by adjusting thermostat down to open
THl and TH2, or by momentarily switching thermostat sub­
base to the OFF position. If compressor oil pressure is lost
or if oil pressure fails to build on start-up on either refrig­
eration circuit, an oil-pressure safety switch shuts off the
affected compressor. The switch must be reset manually at
the unit.
IMPORTANT: Do not reset more than once! If oil
pressure switch trips, determine cause and correct. Do
not bypass oil pressure safety switch.
If crankcase heater is defective, the compressor in the af­
fected circuit is locked off. The circuit remains off until the
crankcase heater is replaced.
Manufacturer reserves the right to discontinue, or change at any time, specifications or designs without notice and without incurring obligations.
Book 11 PC 111 Catalog No 563-710 Printed in U S. A Form 38QP-5SI Pg 6 11-92 Replaces; New
Tab 5a