Carrier 50WQ - Manual (Page 5)

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CURRENT AND TEMPERATURE SENSITIVE
OVERLOAD (linebreak) internal on all com­
pressors except on 50WQ014 which has external
shell mounted overload. Overload resets auto­
matically when internal compressor motor tempera­
ture drops to a safe level (overloads may require up
to 45 minutes to reset). When an internal overload
is suspected of being open, check by using an ohm-
meter or continuity tester. If necessary, refer to
Carrier Standard Service Techniques Manual,
Chapter 2, for complete instructions.
HIGH-PRESSURE SWITCH opens and shuts
compressor off if discharge pressure rises above
395 psig. Switch closes at 295 psig.
FREEZE-UP PROTECTION — Two controls are
used to prevent unit from operating if water
approaches freezing temperature during heating
cycle.
► 1. Low Water Temperature Cutout (LWTC) —
shuts unit off and energizes lockout relay if
water temperature reaches 37 F.
2. Lockout Relay — locks itself in energized posi­
tion and prevents unit from starting.
The unit can be restored to heating operation if
the water temperature rises to 42 F, where the
LWTC will reset, and if the thermostat circuit is
interrupted either by lowering the thermostat setting
or by moving system switch to OFF or COOL.
Thermostat may then be readjusted to normal set
point.
->HEAT PUMP CIRCUITS shown in Fig. 4 are
refrigerant and water flow diagrams for heating and
cooling cycles. Schrader service port located be­
tween the reversing valve and the heat exchanger
permits field installation of swivel tee (Carrier Part
No. DD44CA051) for connecting water regulating
valves without losing refrigerant charge.
WATER REGULATING VALVES control water
flow to yield optimum performance in both the
heating and cooling modes.
In cooling, the controlling valve is actuated by
head pressure. As the head increases, the valve opens
and allows more water to flow. If the supply water is
very cold, the head pressure will drop, causing the
valve to throttle back.
In heating, the direct-acting valve is closed due to
very low pressure. The other valve is reverse-acting
and opens on a drop in suction pressure. If the water
temperature drops, the suction pressure will also
drop causing the valve to open. This allows more
water to flow, thereby preventing freeze-up. It also
throttles back if the inlet water temperature rises.
HEATING CYCLE COOLING CYCLE
Water In/Water Out can be to a ground water or surface water source
Fig. 4 — 50WQ Refrigerant and Water Flow Diagrams