Testing Relays - Komatsu PC88MR-10 Shop Manual

Testing relays

(PC220-K5FE-001-K-00-A)
Place the machine on a level ground, lower the work equipment to the ground and stop the engine.
Turn the battery disconnect switch to the OFF position and remove the key.
a Note the connector numbers and installed positions before disconnecting wiring harnesses and hoses.
Testing
(PC88MR-K5FE-360-K-00-A)
a If air conditioner compressor is normal (air is cooled), skip the test.
Compressor clutch relay R21:
Turns the air conditioner compressor (clutch) ON/OFF.
a See Step 2 in "Parts and connectors layout".
1. Check the condition of contact of connector R21. (Check whether it is securely in place.)
2. Turn the starting switch ON (engine stopped), turn on the main power to the air conditioner, then turn the
air conditioner switch ON. The compressor relay is turned on if the air conditioner status is normal. Check
that a click is heard.
a The air conditioner controller will not turn on the compressor clutch relay in the following cases.
When the evaporator temperature is 3 °C or below (indicated by the evaporator temperature sensor)
When the dual pressure switch detects abnormal pressure (the dual pressure switch is OFF)
Checking relay unit
a Since no T-adapter is available, it is impossible to check the relay while the voltage is applied to the coil
actually.
Compressor clutch relay (R21), air conditioner compressor connector (AC03)
Coil resistance between terminals (1) and (2) is 300 to 500 z
While voltage (20 to 30 VDC) is not applied between terminals (1) (+) and (2), terminals (3) and (4) are
connected.
While voltage (20 to 30 VDC) is applied between terminals (1) (+) and (2), terminals (3) and (5) are
connected.
PC88MR-10
80 Appendix

Testing relays

80-47