CARRIER-PLANETARY 7T7377 - Caterpillar

Diagnostics
Check the pressure. See "Specifications".
If the pressure is more than the low pressure or less than the high pressure, proceed to Step 3. If the pressure is less than or the same as the low pressure, or the pressure is greater than or the same as the high pressure, proceed to Step 4.
Check the cooling cycle.
Disconnect the connector from the sensor.
Measure for continuity between the two terminals of the pressure switch.
If continuity does not exist between the two terminals proceed to Step 7. If continuity does exist between the two terminals, proceed to Step 8.
Replace the pressure switch.
Disconnect the harness from the control unit.
Measure the voltage between terminals 4 of the control unit and the body ground. See "Specifications".
If the voltage values are incorrect, proceed to Step 11. If the voltage value is correct proceed to Step 12.
Replace the control unit.
Check for power at wire BK/RD and check for ground at wire BK of the sensor connector while the harness is connected to the control unit.
If power and ground are found the circuit is not open. Proceed to Step 15. If power and ground are not found, proceed to Step 14.
Check the harness and repair the harness between the connectors at the control unit to the connectors at the sensor for wire BK/RD and wire BK.
Reconnect the harness to the sensor.Specifications
Low pressure ... 0.20 MPa (29 psi)High pressure ... 2.9 MPa (420 psi)System voltage ... 24 Volts