Carrier SINGLE PACKAGED ELECTRIC COOLING UNITS 50GS Installation And Operating Instructions Manual

Also see for 50GS018 Guide: Manual

Contents

When evaluating the refrigerant charge, an indicated adjust-ment to the specified factory charge must always be veryminimal. If a substantial adjustment is indicated, an abnormalcondition exists somewhere in the cooling system, such asinsufficient 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- andhigh-pressure gauge hoses to low- and high-pressure servicefittings, respectively.3. Start unit in Cooling mode and let unit run until systempressures 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) todetermine desired system operating suction line temperature.See Fig. 15-27.6. Compare actual suction-tube temperature with desiredsuction-tube temperature. Using a tolerance of ±3°F, addrefrigerant if actual temperature is more than 3°F higher thanproper suction-tube temperature, or remove refrigerant ifactual temperature is more than 3°F lower than requiredsuction-tube temperature.NOTE: If the problem causing the inaccurate readings is arefrigerant leak, refer to Check for Refrigerant Leaks section.INDOOR AIRFLOW AND AIRFLOW ADJUSTMENTSFor cooling operation, the recommended airflow is 350 to 450cfm for each 12,000 Btuh of rated cooling capacity.Tables 8 and 9 show cooling airflows at various external staticpressures. Refer to these tables to determine the airflow for thesystem 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 tagbefore changing blower speed. Electrical shock can causeserious injury or death.Airflow can be changed by changing the lead connections of theblower motor.Unit 50GS two- or three-speed motors (except size 030) arefactory wired for low speed operation. Unit 50GS030 is factorywired for medium speed.All 50GX units are factory wired for low speed and may need tobe wired for medium or high speed in the field.FOR 208/230VFor color coding on the 208/230V motor leads, see Table 6.To change the speed of the indoor fan motor (IFM), remove the fanmotor speed leg lead from the time delay relay (TDR). This wireis attached to terminal–3 of TDR for single-phase and 3-phaseunits. To change the speed, remove and replace with lead fordesired blower motor speed. Insulate the removed lead to avoidcontact with chassis parts.FOR 460-V GE MOTORSFor color coding on the 460-v GE motor leads, see Table 7.To change the speed of the indoor fan motor (IFM), remove fanmotor speed lead from the time delay relay (TDR) and replace withthe lead for the desired blower motor speed. The motor speed leadis attached to terminal–3 of TDR. For low and medium speedsblack must be connected to the jumper wire. Insulate removed leadend to avoid contact with chassis parts. To select high speed on460-v GE motors, separate the black female quick connect (QC)from the jumper lead male quick connect (QC) and connect theblack lead to the BR. Insulate the jumper to avoid contact with anychassis parts.COOLING SEQUENCE OF OPERATIONWith the room thermostat SYSTEM switch in the COOL positionand the FAN switch in the AUTO position, the cooling sequenceof operation is as follows:When the room temperature rises to a point that is slightly abovethe cooling control setting of the thermostat, the thermostatcompletes the circuit between thermostat terminal R to terminals Yand G. These completed circuits through the thermostat connectcontactor coil (C) (through unit wire Y) and time delay relay(TDR) (through unit wire G) across the 24-v secondary oftransformer (TRAN).The normally open contacts of energized contactor (C) close andcomplete 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 closeand complete the circuit through evaporator blower (indoor) fanmotor (IFM).NOTE: Once the compressor has started and then has stopped, itshould not be started again until 5 minutes have elapsed.The cooling cycle remains “on” until the room temperature dropsto a point that is slightly below the cooling control setting of theroom thermostat. At this point, the thermostat “breaks” the circuitbetween thermostat terminal R to terminals Y and G. These opencircuits deenergize contactor coil C and relay coil TDR. Thecondenser 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.MAINTENANCETo ensure continuing high performance, and to minimize thepossibility of premature equipment failure, periodic maintenancemust be performed on this equipment. This cooling unit should beTable 6—Color Coding for 208/230–V Motor Leads3-SPEED 2-SPEEDblack = high speed black = high speedblue = medium speed -red = low speed red = low speedTable 7—Color Coding for 460-V GE Motor Leads3-SPEED 2-SPEEDblack = high black = highviolet = jumper blue = jumperorange = medium -red = low red = low18