Carrier 50CR Detail A, SystemInformation, Troubleshooting, Start-Upchecklist

Step 14—System Information

LOSS-OF-CHARGE SWITCH

The loss of charge switch is a protective device wired into control circuit (low voltage). It shuts off the compressor if abnormally low pressures are present in the refrigeration circuit.

NOTE: Because these switches are attached to refrigeration system under pressure, it is not advisable to remove this device for troubleshooting unless you are reasonably certain that a problem exists. If switch must be removed, remove and recover all system charge so that pressure gauges read 0 psi. Never open system without breaking vacuum with dry nitrogen.

CHECK DEFROST THERMOSTAT

There is a liquid header with a brass distributor and feeder tube going into outdoor coil. At the end of one of the feeder tubes, there is a 3/8-in. OD stub tube approximately 3 in. long (See Fig. 27). The defrost thermostat should be located on stub tube.

NOTE: There is only one stub tube used with liquid header, and on most units it is the bottom circuit.

The defrost thermostat signals heat pump that conditions are right for defrost or that conditions have changed to terminate defrost. It is a thermally-actuated switch clamped to outdoor coil to sense its temperature. Normal temperature range is closed at 30° ± 3°F and open at 80° ± 5°F.

TROUBLESHOOTING

Refer to the Cooling and Heating Troubleshooting Chart (Table 7) for troubleshooting information.

START-UP CHECKLIST

Use the Start-Up Checklist at the back of this manual.

Unit Top

Defrost

Sensor

Detail A

See

Detail A

A06068

Fig. 27 - Defrost Sensor Location

28