Carrier 38MGR Series Service Manual page 63

DIAGNOSIS AND SOLUTION (CONT)
The cooling operation or heating operation does not operate
Probable cause:
4-way valve faulty
Check the 4-way valve. See "4-Way Valve" on page 68 for more information.
When cooling, the heat exchanger of the non-operating indoor unit frosts. When heating, the non-operating indoor unit gets warm.
Probable causes:
• EXV faulty
• Wire and tubing connected in reverse
• Check the EXV.
Temperature Sensor Checking
Disconnect the temperature sensor from PCB, and measure the resistance value with a tester.
Fig. 67 — Tester
Temperature Sensors
Room temp.(T1) sensor,
Indoor coil temp.(T2) sensor,
Outdoor coil temp.(T3) sensor,
Outdoor ambient temp.(T4) sensor,
Compressor discharge temp.(T5) sensor.
Measure the resistance value of each winding by using the multi-meter.
63
38MGR-04SM Specifications subject to change without notice.