Carrier 50HQ - Manual (Page 7)

I
meter or continuity tester. If necessary, refer to
Carrier Standard Service Techniques Manual,
Chapter 2, for complete instructions.
HIGH-PRESSURE SWITCH closes and shuts
compressor off if discharge pressure rises above 395
psig. Switch opens at 295 psig.
FREEZE-UP PROTECTION — Two controls are
used to prevent unit from operating if water
approaches freezing temperature:
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 position
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. 8, are
refrigerant and water flow diagrams for heating
and cooling cycles.
SERVICE
Refrigerant Charging — Unit refrigerant system
is factory charged. When recharging is necessary
during heating or cooling season, weigh in total
charge indicated in Table 4. Remove any refrigerant
remaining in system before recharging. If system has
lost complete charge, evacuate system to 500
microns (29.7 in. vacuum) before recharging.
Service port connections are provided on high and
low sides of refrigerant system for evacuation and
charging. (See Fig. 8 for service port location.)
Dial-a-charge charging cylinder is an accurate
device used to recharge systems by weight. These
cylinders are available at refrigeration supply firms.
To check and/or adjust refrigerant charge during
cooling season, use correct Cooling Cycle Charging
^ Chart (Fig. 9, 11, 13, 15,17,19,21,22,23) or Carrier
Chargemaster® charging device (Carrier Part No.
38GC680004). Charging charts or Chargemaster
may also be used as alternate methods of recharging
system. Charging methods are described below.
To cheek system operation during heating cycle,
use correct Heating Cycle Operation Check Chart
(Fig. 10, 12, 14, 16, 18, 20). These charts indicate
whether a correct relationship exists between unit
operating pressures and water temperature leaving
heat exchanger. If pressure and water temperature
lines do not intersect on chart, the system refrigerant
charge may not be correct or other system abnor­
malities may exist. Do not use Operation Check
Charts to adjust refrigerant charge. Weigh charge
into system.
COOLING CYCLE HEATING CYCLE
Fig. 8 — Refrigerant and Water Flow Diagrams — 50HQ,VQ