Carrier 50TJ016-028 Installation, Start-Up And Service Instructions Manual page 30

BOTH CIRCUITS
ALL OUTDOOR FANS MUST BE OPERATING
Fig. 42 — Cooling Charging Chart — SI
BOTH CIRCUITS
ALL OUTDOOR FANS MUST BE OPERATING
Fig. 43 — Cooling Charging Chart — English
Filter Drier —
Replace whenever refrigerant system is
exposed to atmosphere.
Protective Devices
COMPRESSOR PROTECTION
Overtemperature — Each compressor has an internal protec-
tor to protect it against excessively high discharge gas
temperatures.
Overcurrent — Each compressor has an internal line break
motor protection, except the circuit no. 1 on the 50TJ028 unit.
Compressor no. 1 on the 50TJ028 unit uses an electronic mod-
ule located with the compressor junction box, to provide motor
protection. This electronic module monitors winding and
discharge temperatures. If these temperatures reach the trip
values, the module interrupts the control line and causes the
compressor to switch off.
Crankcase Heater — Only 50TJ028 and units with
MoistureMiser are equipped with a 70-watt crankcase heater to
prevent absorption of liquid refrigerant by oil in the crankcase
when the compressor is idle. The crankcase heater is energized
whenever there is a main power to the unit and the compressor
is not energized.
IMPORTANT: After a prolonged shutdown or servicing,
energize the crankcase heaters for 24 hours before starting
the compressors.
Compressor Lockout — If any of the safeties (high-, low-
pressure, freeze protection thermostat, compressor internal
thermostat) trip, or if there is loss of power to the compressors,
the CLO (Compressor Lockout) will lock the compressors off.
To reset, manually move the thermostat setting.
ELECTRONIC MOTOR
(SIZE 016-028 UNITS) — The electronic protection module
is used on compressors on 50TJ units. This system utilizes the
temperature dependent resistance of thermistors to read motor
winding temperature. Four thermistors, connected in series, are
embedded in the motor windings. An electronic module pro-
cesses the resistance values and trips a control relay depending
on the thermistor resistance.
For protection in case of blocked rotor, a thermistor (for
each phase) is embedded in the winding heads on the upper
(suction gas) side of the compressor motor. A fourth thermistor
is located in the winding head at the lower end of the motor. A
fifth sensor is located in the discharge port to control discharge
gas superheat.
The thermistors are connected to the electronic protection
module at terminals S1 and S2.
When the resistance of any thermistor reaches tripping val-
ue, the electronic protection module interrupts the control line
and causes the compressor to switch off. The control line con-
tacts between M1 and M2 are normally open, and close when
24v power is applied to T1 and T2. The electronic protection
module will open the contacts between M1 and M2 if the resis-
tance is in excess of 4500 ± 900 ohms, and will reset at 2750
± 450 ohms.
After the thermistor has cooled off sufficiently, its resistance
will drop to the reset value. The electronic protection module,
however, resets after a time delay of 30 minutes. In addition,
the compressor lockout will need to be reset in order for the
compressor to re-start. Resetting of the lockout is accomplished
by briefly removing power from Y1 and Y2.
ELECTRONIC PROTECTION MODULE FUNCTIONAL
TEST — Prior to start-up of the compressor, a functional
check of the electronic protection module should be done. Per-
form the following procedure to complete the functional
check:
1. Switch off unit power at the unit mounted disconnect
and lock out handle.
2. Disconnect one terminal, either S1 or S2, from the elec-
tronic protection module.
3. Return power to unit. Compressor should not start. If
compressor starts, perform electronic protection module
failure detection procedure below.
4. Switch off unit power.
5. Reconnect the disconnected thermistor lead.
6. Return power to unit. Compressor should start. If com-
pressor does not start, perform electronic protection mod-
ule failure detection procedure below.
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PROTECTION MODULE