Component Tests and General Diagnostics

Thermo Sensors

Fig. 17 Testing Single Terminal Thermo Sensors:

1. Drain cooling system, then remove thermo sensors from radiator.
2. Submerge sensor end of thermo sensor as shown in Fig. 17.
3. Connect ohmmeter across thermo sensor terminal and casing, then heat water.
4. On Radiator fan motor thermo sensor, when water temperature reaches approximately 189-199°F, the thermo sensor contacts should close and continuity should exist between sensor terminal and casing.
5. On condenser fan motor thermo sensor, when water temperatures reach approximately 207-217°F, the thermo sensor contacts should close and continuity should exist between sensor terminal and casing.

Relay Testing

Fig. 18 Radiator Relay Terminal Identification. 1989-90 Sigma:

Fig. 19 Condenser Relay Terminal Identification. 1989-90 Sigma:

1. With radiator fan relay disconnected, use suitable ohmmeter to check for continuity between terminals 2 and 4 Fig. 18, continuity should exist. Check for continuity between terminals 1 and 3, continuity should not exist.
2. Apply battery positive voltage to terminal 2 and battery negative to terminal 4, then check for continuity between terminals 3 and 4, continuity should exist.
3. With condenser fan relay disconnected, use suitable ohmmeter to check for continuity between terminals 2 and 4 Fig. 19, continuity should exist. Check for continuity between terminals 1 and 3, continuity should not exist.
4. Apply battery positive voltage to terminal 2 and battery negative to terminal 4, then check for continuity between terminals 3 and 4, continuity should exist.
5. If relays do not perform as outlined above, replace.

Thermo Sensors

Fig. 20 Relay Terminal Identification. 1989-90 Sigma:

1. Disconnect fan motor connection.
2. Apply battery positive voltage to terminal 6 and battery negative to terminal 3, as shown in Fig. 20. Motor should operate smoothly.