Safety Devices —
Chillers contain many safety devices
and protection logic built into electronic control. Following is a
brief summary of major safeties.
COMPRESSOR PROTECTION
Circuit Breaker — One manual-reset, calibrated-trip magnetic
circuit breaker for each compressor protects against overcur-
rent. Do not bypass or increase size of a breaker to correct
problems. Determine cause for trouble and correct before
resetting breaker. Circuit breaker must-trip amps (MTA) are
listed on individual circuit breakers, and on unit label
diagrams.
30GTN,R and 30GUN,R070 (50 Hz), 080-110 and 230B-
315B Compressor Protection Board (CPCS) — The CPCS is
used to control and protect compressors and crankcase heaters.
Board provides following features:
• compressor contactor control
• crankcase heater control
• ground current protection
• status communication to processor board
• high-pressure protection
One large relay is located on CPCS that controls crankcase
heater and compressor contactor. In addition, this relay pro-
vides a set of contacts that the microprocessor monitors to de-
termine operating status of compressor. If the MBB determines
that compressor is not operating properly through signal con-
tacts, control locks compressor off.
The CPCS contains logic that can detect if current-to-
ground of any winding exceeds 2.5 amps; if so, compressor
shuts down.
A high-pressure switch with a trip pressure of 426 ± 7 psig
(2936 ± 48 kPa) is mounted on each compressor; switch setting
is shown in Table 34. Switch is wired in series with the CPCS.
If switch opens, CPCS relay opens, processor detects it through
signal contacts, and compressor locks off. A loss-of-charge
switch is also wired in series with the high-pressure switch and
CPCS.
If any of these switches opens during operation, the com-
pressor stops and the failure is detected by the MBB when sig-
nal contacts open. If lead compressor in either circuit is shut
down by high-pressure switch, ground current protector, loss of
charge switch, or oil pressure switch, all compressors in the cir-
cuit are locked off.
30GTN,R and 30GUN,R 130-210, 230A-315A and
330A/B-420A/B — A control relay in conjunction with a
ground fault module replaces the function of the CPCS
(above). To reset, press the push-button switch (near the Mar-
quee display).
Table 34 — Pressure Switch Settings,
psig (kPa)
SWITCH
CUTOUT
CUT-IN
High Pressure
426 ± 7
320 ± 20
30GTN,R Units
(2936 ± 48)
(2205 ± 138)
High Pressure
280 ± 10
180 ± 20
30GUN,R Units
(1830 ± 69)
(1240 ± 138)
Loss-of-Charge
7 (48.2)
22 (151.6)
LOW OIL PRESSURE PROTECTION — Lead
compres-
sor in each circuit is equipped with a switch to detect low oil
pressure. Switch is connected directly to processor board.
Switch is set to open at approximately 5 psig (35 kPa) and to
close at 9 psig (62 kPa) maximum. If switch opens when
compressor is running, CR or processor board stops all com-
pressors in circuit. During start-up, switch is bypassed for
2 minutes.
CRANKCASE HEATERS — Each compressor has a 180-w
crankcase heater to prevent absorption of liquid refrigerant by
oil in crankcase when compressor is not running. Heater power