Loss-of-Charge — A pressure switch connected to high side
of each refrigerant circuit protects against total loss-
of-charge. Switch settings are listed in Table 18. If switch
is open, unit cannot start; if switch opens during operation,
unit locks out and cannot restart until switch is closed. Low
charge is also monitored by the processor when an EXV is
used.
A low charge is detected by monitoring EXV position and
superheat entering the compressor. If EXV is wide open, super-
heat is greater than 50 F (28 C) and saturated cooler suc-
tion is less than 55 F (13 C), circuit is stopped and locked
off.
Relief Devices —
Fusible plugs are located in each cir-
cuit to protect against damage from excessive pressures.
HIGH-SIDE PROTECTION — One device is located be-
tween condenser and filter drier; a second is on filter drier.
These are both designed to relieve pressure on a temperature
rise to approximately 210 F (99 C).
LOW-SIDE PROTECTION — A device is located on suc-
tion line, designed to relieve pressure on a temperature rise
to approximately 170 F (77 C).
PRESSURE RELIEF VALVES — Where relief valves are
installed, there is one in each circuit. The valves are de-
signed to relieve at 450 psig (3103 kPa). These valves should
not be capped. If a valve relieves, it should be replaced. If
valve is not replaced, it may relieve at a lower pressure, or
leak due to trapped dirt from the system which may prevent
resealing.
The pressure relief valves are equipped with a
3
⁄
8
-in. SAE
flare for field connection. Some local building codes require
that relieved gases be removed. This connection will allow
conformance to this requirement.
Other Safeties —
There are several other safeties that
are provided by microprocessor control. For details refer to
Controls and Troubleshooting literature.
Copyright 1996 Carrier Corporation
Manufacturer reserves the right to discontinue, or change at any time, specifications or designs without notice and without incurring obligations.
Book 2
Tab
5c
PC 903
Catalog No. 533-005
Printed in U.S.A.
Form 30GT-50SI
Pg 68
12-96
Replaces: 30GT-45SI
