Carrier WEATHERMASTER III 38HQ - Manual (Page 10)

sor no. 1 starts. At the same time, the outdoor fan
motor (OFM) starts and the defrost timer (DT) is
energized although it is not functional in the
cooling mode; the indoor fan relay (IFR) is
energized and the indoor fan motor (IFM) starts.
Compressor no. 2 does not run in COOL mode.
When the second stage of cooling is satisfied, Cl
opens. The compressor stops; the indoor and out­
door fans stop; DT is de-energized. When the con­
trolled temperature drops approximately 1 F below
the cooling set point, Co opens. RVS is de-energized
and the reversing valve switches to heating (normal
position). The unit is shut down except for the two
compressor crankcase heaters, which remain on as
long as the field power supply is on.
THERMOSTAT CALLS FOR HEATING (The
reversing valve is de-energized, in heating position.)
1. First stage heating thermostat (HI) closes. Com­
pressor contactor no. 1 (Cl) is energized and
compressor starts; outdoor fan motor (OFM)
starts; defrost timer (DT) is energized. Indoor
fan relay (IFR) is energized and indoor fan
motor (IFM) starts. When the outdoor ambient
switch (OA) closes (at first thermal balance
point), compressor contactor no. 2 (C2) is ener­
gized and compressor no. 2 starts. Compressor
no. 1 and compressor no. 2 operate simul­
taneously as long as OA is closed. The crankcase
heaters are de-energized when both compressors
are running.
2. Second-stage heating thermostat (H2) closes and
activates the first accessory heater element
sequencer thru indoor thermostat terminal W2.
The first-stage electric heater element is energized
immediately and the other heater elements are
energized at regular intervals thru the sequencers.
Separate outdoor thermostats may be used to
energize the second sequencer and bring on addi­
tional heater elements if more incremental heat
control is desired.
When the second stage of heating is satisfied, H2
opens and the electric heater(s) shuts off. When the
first stage of heating is satisfied, HI opens and the
unit shuts down, except for the compressor crank­
case heater, which remains on as long as the field
power supply is on.
Unit Controls and Safety Devices
HIGH-PRESSURE RELIEF VALVE is located in
compressor. Relief valve opens at a pressure
differential of approximately 500 psi between
suction (low side) and discharge (high side) to allow
pressure equalization.
INTERNAL CURRENT AND TEMPERATURE
SENSITIVE OVERLOAD resets automatically
when internal compressor motor temperature drops
to a safe level (overloads may require up to 45 min­
utes to reset). When an internal overload is suspected
of being open, check by using an ohmmeter or con­
tinuity tester. If necessary, refer to Carrier Standard
Service Techniques Manual, Chapter 2, Electrical,
for complete instructions.
LOW-PRESSURE SWITCH is located in compres­
sor section on suction line between reversing valve
and accumulator. Provides loss-of-charge protec­
tion by shutting compressor off if suction pressure
drops below setting. Low-pressure switch settings
are: open, 5 ± 3 psig; close, 20 ± 5 psig.
CRANKCASE HEATERS are activated by a relay.
Heaters derive power from contactor no. 2 and are
energized when compressors are off or when only
one compressor is functioning.
The heater keeps the crankcase warm during the
off cycle and thus prevents dilution of the oil with
the refrigerant, assures good lubrication, and pre­
vents loss of oil from crankcase during start-up.
If the electrical disconnect switch to the compres­
sor section has been off for an extended period of
time, the crankcase heater should be energizedfor 24
hours before starting the compressor.
SIGNAL-LOC™ SYSTEM MALFUNCTION
WARNING INDICATOR AND LOCKOUT —
Indoor compressor section is equipped with a solid-
state warning logic circuit that protects the system.
In case of a malfunction (compressors do not oper­
ate due to safety device cutout), emergency heat light
on thermostat comes on and compressors are pre­
vented from restarting. Compressors can be re­
started after resetting thermostat (turn thermostat
off then on). If either compressor malfunctions,
both will be locked out (prevented from restarting).
The emergency heat light goes out when com­
pressors are restarted or when indoor thermostat is
satisfied. If the light does not stay out after two or
three attempts to restart, check for cause of
malfunction.
DEFROST CONTROL, consisting of a defrost
timer, defrost thermostat and defrost relay, inter­
rupts normal system heating operation every 90
minutes to defrost outdoor coil, if the coil saturated
suction temperature indicates freezing tempera­
tures. Defrost control simultaneously stops outdoor
fan, energizes reversing valve solenoid to return
system to cooling cycle (outdoor coil as condenser,
indoor fan-coil unit as evaporator), and activates
accessory electric heater.
For the heat pump to defrost, 2 conditions are
necessary;
1. Defrost timer contacts must be closed.
2. Refrigerant temperature from outdoor unit must
be cold enough to cause defrost thermostat
contacts to close. Contacts close at 27 (± 4) F.
Every 90 minutes of elapsed running time, the de­
frost timer contacts close for 10 seconds. If the
defrost thermostat contacts are closed, the unit
defrosts. The defrost timer limits defrosting period
to 10 minutes. Normally the frost is removed and the
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