When evaluating the refrigerant charge, an indicated adjust- ment to the specified factory charge must always be very minimal. If a substantial adjustment is indicated, an abnormal condition exists somewhere in the cooling system, such as insufficient airflow across either coil or both coils.
Proceed as follows:
1.Remove caps from low- and high-pressure service fittings.
2.Using hoses with valve core depressors, attach low- and high-pressure gauge hoses to low- and high-pressure service fittings, respectively.
3.Start unit in Cooling mode and let unit run until system pressures stabilize.
4.Measure and record the following:
a.Outdoor ambient-air temperature (°F db).
b.Evaporator inlet-air temperature (°F wb).
c.Suction-tube temperature (°F) at low-side service fitting.
d.Suction (low-side) pressure (psig).
5.Using “Cooling Charging Charts” compare outdoor-air tem- perature (°F db) with the suction line pressure (psig) to determine desired system operating suction line temperature. See Fig. 15-27.
6.Compare actual suction-tube temperature with desired suction-tube temperature. Using a tolerance of ±3°F, add refrigerant if actual temperature is more than 3°F higher than proper suction-tube temperature, or remove refrigerant if actual temperature is more than 3°F lower than required suction-tube temperature.
NOTE: If the problem causing the inaccurate readings is a refrigerant leak, refer to Check for Refrigerant Leaks section.
INDOOR AIRFLOW AND AIRFLOW ADJUSTMENTS
For cooling operation, the recommended airflow is 350 to 450 cfm for each 12,000 Btuh of rated cooling capacity.
Tables 8 and 9 show cooling airflows at various external static pressures. Refer to these tables to determine the airflow for the system being installed.
NOTE: Be sure that all supply- and return-air grilles are open, free from obstructions, and adjusted properly.
Disconnect electrical power to the unit and install lockout tag before changing blower speed. Electrical shock can cause serious injury or death.
Airflow can be changed by changing the lead connections of the blower motor.
Unit 50GS two- or three-speed motors (except size 030) are factory wired for low speed operation. Unit 50GS030 is factory wired for medium speed.
All 50GX units are factory wired for low speed and may need to be wired for medium or high speed in the field.
FOR 208/230V
For color coding on the 208/230V motor leads, see Table 6.
To change the speed of the indoor fan motor (IFM), remove the fan motor speed leg lead from the time delay relay (TDR). This wire is attached to terminal–3 of TDR for single-phase and 3-phase
Table 6—Color Coding for 208/230–V Motor Leads
3-SPEED | 2-SPEED |
black = high speed | black = high speed |
blue = medium speed | - |
red = low speed | red = low speed |
units. To change the speed, remove and replace with lead for desired blower motor speed. Insulate the removed lead to avoid contact with chassis parts.
FOR 460-V GE MOTORS
For color coding on the 460-v GE motor leads, see Table 7.
Table 7—Color Coding for 460-V GE Motor Leads
3-SPEED | 2-SPEED |
black = high | black = high |
violet = jumper | blue = jumper |
orange = medium | - |
red = low | red = low |
| |
To change the speed of the indoor fan motor (IFM), remove fan motor speed lead from the time delay relay (TDR) and replace with the lead for the desired blower motor speed. The motor speed lead is attached to terminal–3 of TDR. For low and medium speeds black must be connected to the jumper wire. Insulate removed lead end to avoid contact with chassis parts. To select high speed on 460-v GE motors, separate the black female quick connect (QC) from the jumper lead male quick connect (QC) and connect the black lead to the BR. Insulate the jumper to avoid contact with any chassis parts.
COOLING SEQUENCE OF OPERATION
With the room thermostat SYSTEM switch in the COOL position and the FAN switch in the AUTO position, the cooling sequence of operation is as follows:
When the room temperature rises to a point that is slightly above the cooling control setting of the thermostat, the thermostat completes the circuit between thermostat terminal R to terminals Y and G. These completed circuits through the thermostat connect contactor coil (C) (through unit wire Y) and time delay relay (TDR) (through unit wire G) across the 24-v secondary of transformer (TRAN).
The normally open contacts of energized contactor (C) close and complete the circuit through compressor motor (COMP) to con- denser (outdoor) fan motor (OFM). Both motors start instantly.
The set of normally open contacts of energized relay TDR close and complete the circuit through evaporator blower (indoor) fan motor (IFM).
NOTE: Once the compressor has started and then has stopped, it should not be started again until 5 minutes have elapsed.
The cooling cycle remains “on” until the room temperature drops to a point that is slightly below the cooling control setting of the room thermostat. At this point, the thermostat “breaks” the circuit between thermostat terminal R to terminals Y and G. These open circuits deenergize contactor coil C and relay coil TDR. The condenser and compressor motors stop. After a 30-second delay, the blower motor stops. The unit is in a “standby” condition, waiting for the next “call for cooling” from the room thermostat.
MAINTENANCE
To ensure continuing high performance, and to minimize the possibility of premature equipment failure, periodic maintenance must be performed on this equipment. This cooling unit should be
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