Carrier 50SZ Series Installation, Start-up And Service Instructions Manual

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Contents

Step 8—Metering deviceRefrigerant metering devices are fixed orifices and are located inthe inlet header to the indoor and outdoor coils.Step 9—Liquid line strainersThe liquid line strainers (to protect metering devices) are made ofwire mesh and are located in the liquid lines on the inlet side of themetering devices.Step 10—High Flow ValvesHigh flow valves are located on the compressor hot gas andsuction tubes. Large black plastic caps distinguish these valveswith O-rings located inside the caps. These valves can not beaccessed for service in the field. Ensure the plastic caps are inplace and tight or the possibility of refrigerant leakage could occur.Step 11—Time-delay relayThe Time-Delay Relay (TDR) is a solid-state control, recycledelay timer which keeps indoor blower operating for 60 sec. afterthermostat is satisfied. This delay enables blower to removeresidual cooling in coil after compression shutdown, therebyimproving efficiency of system. The sequence of operation is thaton closure of wall thermostat and at end of a fixed on delay of 1sec., fan relay is energized. When thermostat is satisfied, an offdelay is initiated. When fixed delay of 60± 5 sec. is completed, fanrelay is de-energized and fan motor stops. If wall thermostat closesduring this delay, TDR is reset and fan relay remains energized.TDR is a 24-v device that operates within a range of 15-v to 30-vand draws about 0.5 amps. If the blower runs continuously insteadof cycling off when the fan switch is set on AUTO, the TDR isprobably defective and must be replaced.Step 12—Loss of charge switchThe loss of charge switch is located on the outdoor liquid line. Thisswitch contains a Schrader core depressor. This switch opens at 7psig and closes at 22 psig. No adjustment is necessary.NOTE: Because these switches are attached to refrigerationsystem under pressure, it is not advisable to remove this device fortroubleshooting unless you are reasonably certain that a problemexists. If switch must be removed, remove and recover all systemcharge so that pressure gages read 0 psi. Never open systemwithout breaking vacuum with dry nitrogen.Step 13—Check defrost thermostatThere is a liquid header with a brass distributor and feeder tubegoing into outdoor coil. At the end of 1 of the feeder tubes, thereis a 3/8-in. OD stub tube approximately 3 in. long (See Fig. 24).The defrost thermostat should be located on this stub tube. Notethat there is only 1 stub tube used with liquid header, and on mostunits it is the bottom circuit.Step 14—Defrost ThermostatDefrost thermostat signals heat pump that conditions are right fordefrost or that conditions have changed to terminate defrost. It isa thermally actuated switch clamped to outdoor coil to sense itstemperature. Normal temperature range is closed at 30° +/- 3°Fand open at 80° +/- 5°F.NOTE: The defrost thermostat must be located on the liquid sideof the outdoor coil on the bottom circuit and as close to the coil aspossible.TROUBLESHOOTINGRefer to the Cooling and Heating Troubleshooting Chart (Table 9)for troubleshooting information.START-UP CHECKLISTUse the Start-Up Checklist to ensure proper start-up procedures arefollowed.Fig. 21—Defrost Thermostat C99029FEEDER TUBESTUB TUBEDEFROSTTHERMOSTATC99097Fig. 20—Refrigerant Circuit18

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