Carrier 48PG20-28 specifications Protective Devices, Altitude Compensation

Table 32 — Altitude Compensation*

NATURAL GAS

ELEVATION		NATURAL GAS ORIFICE SIZE†
(ft)	Low Heat	Medium Heat	High Heat (6 Cell)	High Heat (8 Cell)
0-1,999	29	30	29	29
2,000	29	30	29	29
3,000	30	31	30	30
4,000	30	31	30	30
5,000	30	31	30	30
6,000	30	31	30	30
7,000	31	32	31	31
8,000	31	32	31	31
9,000	31	32	31	31
10,000	32	33	32	32
*As the height above sea level increases, there is less oxygen per cubic foot of air. Therefore, heat input
rate should be reduced at higher altitudes. Includes a 4% input reduction per each 1000 ft.
†Orifices available through the local Carrier dealer.

PROPANE GAS

ELEVATION		PROPANE GAS ORIFICE SIZE†
(ft)	Low Heat	Medium Heat	High Heat (6 Cell)	High Heat (8 Cell)
0-1,999	35	38	35	35
2,000	36	39	36	36
3,000	36	39	36	36
4,000	37	40	37	37
5,000	37	40	37	37
6,000	38	41	38	38
7,000	39	42	39	39
8,000	40	43	40	40
9,000	41	44	41	41
10,000	42	45	42	42

*As the height above sea level increases, there is less oxygen per cubic foot of air. Therefore, heat input ate should be reduced at higher altitudes. Includes a 4% input reduction per each 1000 ft.

†Orifices available through the local Carrier dealer.

Filter Drier — Replace whenever refrigerant system is ex- posed to atmosphere. Only use factory specified liquid-line filter driers with working pressures no less than 650 psig. Do not install a suction-line filter drier in liquid line. A liquid-line filter drier designed for use with Puron® refrigerant is required for each circuit.

Protective Devices

COMPRESSOR PROTECTION

Overcurrent — Each compressor has internal line break motor protection.

Overtemperature — Each compressor has an internal protector to protect it against excessively high discharge gas temperatures.

High-Pressure Switch — If the high-pressure switch opens, the compressor will shut down and the compressor lockout (CLO) device will energize to block further compressor operation. The high-pressure switch will reset automatically as the refrigerant pressure drops below its reset level. The CLO will remain ener- gized until manually reset or cooling demand is removed.

Low-Pressure Switch — If the low-pressure switch opens, the compressor will shut down and the compressor lockout (CLO) device will energize to block further compressor opera- tion. The low-pressure switch will reset automatically as the refrigerant pressure rises above its reset level. The CLO will remain energized until manually reset or cooling demand is removed.

Freeze Protection Switch — This switch is installed on each evaporator coil section to provide protection against continued unit operation with a frosted evaporator surface. If the freeze protection switch opens, the compressor on this circuit will shut down and the compressor lockout (CLO) device will ener- gize to block further compressor operation. The freeze protec- tion switch will reset as the evaporator tube temperature rises above its reset level. The CLO will remain energized until manually reset or cooling demand is removed.

Compressor Lockout (CLO) Device — The CLO prevents automatic recycling of the compressor as safety controls reset. If the high-pressure switch, low-pressure switch or freeze pro- tection switch opens, the CLO device will energize to block further compressor operation. To reset the CLO (after all safety switches have reset), either open the thermostat to remove the cooling demand signal (and then re-close) or cycle the control power in the unit.

EVAPORATOR FAN MOTOR PROTECTION — A manu- al reset, calibrated 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.

Fuses are also located in the control box and feed power to the condenser fan motors. Always replace blown fuses with the correct size fuse as indicated on the unit fuse label.

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 and are located at the suc- tion line service port. Protect joint during brazing operations near joint.

Control Circuit, 24-V — Each 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. 42-45 for schematics.

Replacement Parts — A complete list of replacement parts may be obtained from any Carrier distributor upon request.

Diagnostic LEDs — The IGC control board has a LED for diagnostic purposes. See Unit Troubleshooting section on page 57 for more information.

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