Carrier 48TJ016-028 - Manual (Page 43)

Gas Valve Adjustment
NATURAL GAS — The gas valve opens and closes in re­
sponse to the thermostat or limit control.
When power is supplied to valve terminals D1 and C2, the
main viilve opens to its preset position.
The regular factoiy setting is stamped on the v;ilve body
(3.3 in. wg).
To adjust regulator:
1. Set thermostat at setting for no call for heat.
2. Turn main gas valve to OFF position.
3. Remove Vs-in. pipe plug from manifold or gas valve
pressure tap connection. Install a suitable pressure­
measuring device.
4. Set main gas valve to ON position.
5. Set thennostat at setting to call for heat.
6. Remove screw cap covering regulator adjustment screw
(see Fig. 56).
7. Turn adjustment screw clockwise to increase pressure or
counterclockwise to decrease pressure.
8. Once desired pressure is established, set thermostat set­
ting for no call for heat, turn off main gas valve, remove
pressure-measuring device, and replace Vs-in. pipe plug
and screw cap.
REGULATOR
ADJUSTMENT
SCREW
(REMOVE
COVER)
Fig. 56 — Gas Valve
Main Burners — For all applications, main burners are
factoiy set and should require no adjustment.
MAIN BURNER REMOVAL
1. Shut off (field-supplied) manual main gas valve.
2. Shut off power to unit.
3. Remove unit control box access panel, burner section ac­
cess panel, and center post (see Fig. 4 and 5).
4. Disconnect gas piping from gas valve inlet.
5. Remove wires from gas valve.
6. Remove wires from rollout switch.
7. Remove sensor wire and ignitor cable from IGC board.
8. Remove 2 screws securing manifold bracket to basepan.
9. Remove 2 screws that hold the burner support plate
flange to the vestibule plate.
10. Lift burner assembly out of unit.
CLEANING AND ADJUSTMENT
1. Remove burner rack from unit as described in Main
Burner Removal section above.
2. Inspect burners, and if dirty, remove burners from rack.
3. Using a soft bnjsh, clean burners and crossover port as
required.
4. Adjust spark gap. See Fig. 57.
5. Reinstall burners on rack.
6. Reinstiill burner rack as described above.
Filter Drier — Replace whenever refrigerant system is
exposed to atmosphere.
Protective Devices
COMPRESSOR PROTECTION
Phase Protection — On 48TJ016 and 020 units, the phase
monitor relay (PMR) will monitor the sequence of the 3-phase
electrical system to provide phase reversal protection. The
PMR will also monitor tlie 3-phase voltage inputs to provide
phase loss protection for tlie 3-phase device.
Overcurrent — Each compressor has internal line break motor
protection, except the circuit no. 1 on the 48TJ028 units. Com­
pressor no. 1 on the 48TJ028 unit uses an electronic module,
located witli the compressor junction box, to provide motor
protection. Tliis electronic module monitors winding and dis-
chaige temperatures. If tliese temperatures reach tlie trip val­
ues, the module interiupts the control line and causes the
compressor to switch off.
Crankcase Heater — Only the 48TJ028 unit and units with
optional MoistureMiSeff^* dehumidification system are
equipped with a 70-watt crankcase heater to prevent absorption
of liquid refrigerant by oil in the crankcase when the compres­
sor 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 horn's before stint­
ing the compressors.
Compressor Lockout — If any of the safeties (high-pressure,
low-pressure, freeze protection thermostat, compressor internal
tliermostat) trip, or if tliere is loss of power to tlie compressors,
tlie cooling lockout (CLO) will lock the compressors off. To
reset, manually move the thermostat setting.
EVAPORATOR-PAN MOTOR PROTECTION — A man­
ual reset, ciilibrated trip, magnetic circuit breaker protects
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 internally protected against
overtemperature.
HIGH-PRESSURE AND LOW-PRESSURE SWITCHES ^
If either switch trips, or if the compressor overtemperature
switch activates, that refrigerant circuit will be automatically
locked out by the CLO. To reset, manually move the thermo­
stat setting.
FREEZE PROTECTION THERMOSTAT (PPT) — An PPT
is located on the top and bottom of the evaporator coil. They
detect frost build-up and turn off the compressor, allowing the
coil to clear. Once the frost has melted, the compressor can be
reenergized by resetting the compressor lockout.
Relief Devices — All units have relief devices to protect
against damage from excessive pressures (i.e., fire). Tliese
devices protect the high and low side.
Control Circuit, 24-V — This control circuit is pro­
tected against overcurrent by a 3.2 amp circuit breaker.
Breaker can be reset. If it trips, determine cause of trouble
before resetting. See Fig. 58 and 59 for typical wiring diagram
and component ai'rangement.
Replacement Parts — a complete list of replacement
parts may be obtained from any Carrier distributor upon
request.
Diagnostic IGC Control LEDs — Tlie IGC bomd
has LEDs for diagnostic purposes. Refer to Troubleshooting
section on page 48.
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