Refrigeration System Startup - LG AR-DR11-08A Installation And Operation Manual

Rooftop dedicated outdoor air systems doas 650 to 12,000 cfm

Table of Contents

GAS HEATER CONNECTION AND STARTUP /

Normal Operation

1. Turn ON electrical supply to unit at

disconnect switch.

Operating and Safety Controls

Combustion Air Pressure Switch

An air pressure switch is provided as part of the control system to verify airflow through induced draft fan (ID fan) by monitoring the differ-

ence in pressure between the ID fan and the atmosphere. If sufficient negative pressure is not present, indicating lack of proper air move-

ment through the heat exchangers, the switch opens shutting off gas supply through the ignition control module. On units with two (2) speed

draft inducer operation, a dual air pressure switch is used, monitoring high and low speed pressures. The air pressure switches have fixed

settings and are not adjustable.

Roll-out Switch (Manual Reset)

The furnace is equipped with manual reset roll-out switches in the event of burner flame roll-out. The switch will open on temperature rise

and shut off gas supply through the ignition control module. Flame roll-out can be caused by insufficient airflow for the burner firing rate (high

gas pressure), blockage of the vent system or in the heat exchanger.

of roll-out condition is identified. The roll-out switch can be reset by pressing the button on the top of the switch.

Primary High Limit Switch

To prevent operation of the furnace under low airflow conditions, the unit is equipped with a fixed temperature high limit switch mounted

on the vestibule panel. This switch will shut off gas to the heater through the ignition control module before the air temperature reaches

250°F. Reduced airflow may be caused by restriction upstream or downstream of the circulating air blower, such as dirty or blocked filters or

restriction of the air inlet or outlet to the unit. The high limit switch will shut-off the gas when the temperature reaches its setpoint and then

automatically reset when the temperature drops to 30°F below the setpoint, initiating a furnace ignition. The furnace will continue to cycle on

limit until the cause of the reduced airflow is corrected.

Ignition Control Module

Ignition control modules are available having a number of different operating functions.

Refrigeration Charge

Upon startup, refrigeration charge must be verified on each circuit by checking superheat and subcooling. Superheat must be measured

at the suction line port nearest the compressor. Subcooling must be measured at the liquid line port nearest the thermal expansion valves

(TXV). All compressors on the circuit must be on at 100% when checking superheat and subcooling. Readings must fall within the ranges

outlined in the table below.

Table 17: Subcooling and Superheat Reading Ranges.

Stage

Subcooling

Superheat

Record superheat and subcooling readings on the startup form. If readings do not fall within the desired ranges, refrigerant charge or thermal

expansion valve adjustments may need to be made. Refer the "Troubleshooting Refrigeration Table" in the Troubleshooting Section on page

112.

When adding refrigerant charge, only use R410A, otherwise the product will be damaged and will malfunction.