Carrier 42QFD048D8S Service Manual page 105

1. IPM Continuity Check
WARNING
Electricity remains in capacitors even when the power supply is off.
Ensure the capacitors are fully discharged before troubleshooting.
1. Turn off outdoor unit and disconnect power supply.
2. Discharge electrolytic capacitors and ensure all energy-storage unit has been discharged.
3. Disassemble outdoor PCB or disassemble IPM board.
4. Measure the resistance value between P and U(V, W, N); U(V, W) and N.
Digital tester
(+)Red (-)Black
P
Resistance value
N
∞
U
(Several MΩ)
V
W

Digital tester
(+)Red
U
V
W
-
Troubleshooting 
Resistance value
(-)Black
N
(Several MΩ)
∞