Carrier 50TJ016-028 Installation, Start-Up And Service Instructions Manual page 31

ELECTRONIC PROTECTION
DETECTION — If the compressor does not operate correctly
during the functional test, this indicates a disturbance in opera-
tion. Perform the following procedure:
1. Switch off unit power at the unit mounted disconnect
and lock out handle.
2. Check the connection of the thermistor leads in the elec-
tronic protection module terminal box for a loose connec-
tion or possible breakage.
3. The resistance of the thermistor chain is measured in a
cold condition (after the motor has sufficiently cooled
down). Measure resistance of the thermistor at the ther-
mistor leads. Disconnect leads from terminals S1 and S2
and measure between the leads. The resistance must be
1250 ohms or lower. If the thermistor has a higher
resistance, it is defective and the compressor must be
replaced.
Use maximum measuring voltage of 3V. Damage to ther-
mistor could occur at higher voltages.
4. If no defect is found with the thermistors, and there is no
loose contact or conductor breakage, the electronic pro-
tection module should be checked. Before checking the
module, remove the connection at terminal M2, then re-
turn control voltage to the module.
a. Check for 24-V between the terminals T1 and T2.
If no voltage is found, check unit wiring.
The voltage should be switched off between voltage tests,
in order to avoid short circuiting or accidental touching of
contacts.
b. With the R lead connected to either Y1 or Y2 as
appropriate, check for 24-V between M1 and chas-
sis ground. If voltage is not found, check unit
wiring.
c. With the thermistor leads removed from terminals
S1 and S2, and 24-V power applied to terminals
T1, T2, and M1, there should not be any voltage
between terminals T2 and M2. If voltage is
present, then the module is defective.
d. With a jumper across module terminals S1 and S2,
and with the R lead connected to either Y1 or Y2
as appropriate, there should be 24 v between termi-
nals M2 and T2. If not, the module is defective.
EVAPORATOR-FAN MOTOR PROTECTION — A man-
ual reset, calibrated trip, magnetic circuit breaker protects
MODULE FAILURE
31
against overcurrent. Do not bypass connections or increase the
size of the breaker to correct trouble. Determine the cause and
correct it before resetting the breaker.
CONDENSER-FAN MOTOR PROTECTION — Each
condenser-fan motor is
overtemperature.
HIGH- AND LOW-PRESSURE SWITCHES — If either
switch trips, or if the compressor overtemperature switch acti-
vates, that refrigerant circuit will be automatically locked out
by the CLO. To reset, manually move the thermostat setting.
FREEZE PROTECTION THERMOSTAT (FPT) — An FPT
is located on the top and bottom of the evaporator coil. It
detects frost build-up and turns off the compressor, allowing
the coil to clear. Once the frost has melted, the compressor can
be reenergized.
Relief Devices —
All units have relief devices to protect
against damage from excessive pressures (i.e., fire). These
devices protect the high and low side.
Control Circuit, 24-V —
tected against overcurrent by a 3.2-amp circuit breaker.
Breaker can be reset. If it trips, determine cause of trouble
before resetting.
EconoMi$er LEDs —
The EconoMi$er control module
has an LED for diagnostic purposes. The flash code identifica-
tion is shown in Table 20.
Optional Hinged Access Doors —
service package is ordered or the if the hinged access doors
option is ordered, the unit will be provided with external and
internal hinged access doors to facilitate service.
Four external hinged access doors are provided. All external
doors are provided with 2 large
bail-type handles. (Compressor access doors have one latch.) A
single door is provided for filter and drive access. One door is
provided for control box access. The control box access door is
interlocked with the non-fused disconnect which must be in the
OFF position to open the door. Two doors are provided for ac-
cess to the compressor compartment.
Two internal access doors are provided inside the filter/
drive access door. The filter access door (on the left) is secured
1
by 2 small / turn latches with folding bail-type handles. This
4
door must be opened prior to opening the drive access door.
The drive access door is shipped with 2 sheet metal screws
holding the door closed. Upon initial opening of the door, these
screws may be removed and discarded. The door is then held
shut by the filter access door, which closes over it.
Replacement Parts —
parts may be obtained from any Carrier distributor upon
request.
internally protected against
This control circuit is pro-
When the optional
1
/ turn latches with folding
4
A complete list of replacement