ENGINE COOLING FAN - ELECTRIC 1990 GENERAL SERVICING Jeep Electric Cooling Fans

Jeep Cherokee 1990 - DESCRIPTION

NOTE:

All 4.0L models with A/C or heavy-duty cooling systems use an auxiliary cooling fan.

An electric cooling fan is mounted behind the radiator. Cooling fan operation is controlled by coolant temperature switch and cooling fan relay.

Jeep Cherokee 1990 - OPERATION

Electric cooling fan is controlled by the cooling fan relay mounted on left inner fender panel. A coolant temperature switch is mounted in the radiator, near the lower radiator hose. When coolant temperature is less than 190?F (88?C), coolant temperature switch contacts are open. When coolant temperature is greater than 190?F (88?C), coolant temperature switch contacts close. This allows current from ignition switch to flow to the relay, allowing contacts of the grounded relay to close. This provides power through the relay for cooling fan operation.

During A/C operation, the Electronic Control Unit (ECU) grounds the A/C relay coil, allowing current to flow through the relay coil. The A/C relay then supplies current to A/C compressor clutch, cooling fan diode assembly and cooling fan relay for cooling fan operation. Whenever A/C is operating, regardless of coolant temperature, cooling fan will operate.

Jeep Cherokee 1990 - TROUBLE SHOOTING COOLING FAN (WITH A/C) COOLING FAN INOPERATIVE

Remove cooling fan relay. See Fig. 1 . Connect battery voltage with 25-amp fuse to Red wire (No. 4 terminal) of cooling fan relay connector. See Fig. 2 . If cooling fan operates, proceed to next step. If cooling fan fails to operate, check continuity of Red wire from cooling fan relay to cooling fan and ground circuit at cooling fan assembly. If continuity exists and ground circuit is okay, replace cooling fan.
With cooling fan relay removed, ensure continuity exists at Black wire (No. 5 terminal) of relay connector and body ground. If continuity exists, proceed to next step. If no continuity exists, repair open or faulty ground.
Connect jumper wire with 25-amp fuse between Red wire (No. 1 terminal) and Red wire (No. 4 terminal) of cooling fan relay connector. Turn ignition on. If cooling fan operates, proceed to next step, leaving jumper wire installed. If cooling fan failed to operate, check for voltage at Green fusible link for cooling fan relay. Fusible links are located near right inner fender panel close to the battery.
Check for voltage at Gray or Orange wire (No. 2 terminal) of cooling fan relay. See Fig. 2 . Ensure voltage exists at Yellow wire of coolant temperature switch connector with ignition on. Install jumper wire across coolant temperature switch terminals.
If cooling fan operates, coolant temperature switch must be checked to ensure continuity exists with coolant temperature greater than 190?F (87?C). If no continuity exists, replace coolant temperature switch and recheck operation.
If coolant temperature switch is okay, check for voltage at Gray or Orange wire (No. 2 terminal) of cooling fan relay. If no voltage exists, replace cooling fan diode assembly.

Jeep Cherokee 1990 - COOLING FAN INOPERATIVE WITH A/C COMPRESSOR

Remove cooling fan relay. Allow engine to idle with A/C turned on. Check for battery voltage at Gray or Orange wire (No. 2 terminal) of cooling fan relay. If no voltage exists, see steps 4) and 5) of COOLING FAN INOPERATIVE under COOLING FAN (WITH A/C).

Jeep Cherokee 1990 - TROUBLE SHOOTING COOLING FAN (WITHOUT A/C) COOLING FAN INOPERATIVE

Remove cooling fan relay. See Fig. 1 . Connect battery voltage with 25-amp fuse to Red wire (No. 4 terminal) of cooling fan relay connector. See Fig. 2 . If cooling fan operates, proceed to next step. If cooling fan fails to operate, check continuity of Red wire from cooling fan relay to cooling fan and ground circuit at cooling fan assembly. If continuity exists and ground circuit is okay, replace cooling fan.
With cooling fan relay removed, ensure continuity exists at Black wire (No. 5 terminal) of relay connector and body ground. If continuity exists, proceed to next step. If no continuity exists, repair open or faulty ground.
Connect jumper wire with 25-amp fuse between Red wire (No. 1 terminal) and Red wire (No. 4 terminal) of cooling fan relay connector. Turn ignition on. If cooling fan operates, proceed to next step, leaving jumper wire installed. If cooling fan did not operate, check for voltage at Green fusible link for cooling fan relay. Fusible links are located near right inner fender panel, close to the battery.
Check for voltage at Gray or Orange wire (No. 2 terminal) of cooling fan relay. Ensure voltage exists at Yellow wire of coolant temperature switch connector with ignition on.
Install jumper wire across coolant temperature switch terminals. If cooling fan operates, coolant temperature switch must be checked to ensure continuity exists with coolant temperature greater than 190?F (87?C). If no continuity exists, replace coolant temperature switch. If cooling fan did not operate, check continuity of wiring from coolant temperature switch to cooling fan relay.

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Fig. 1: Jeep Cherokee 1990 - Component Locations - Cooling Fan Relay Location