THERMOSTATIC FANS
Unit consists of a torque-controlled clutch driven fan. System consists of a silicone filled chamber connecting fan to pulley. (Scheme 1) Fan drive is operated by a control valve. Control valve maintains flow of silicone through drive, and is governed by a temperature sensitive bimetallic coil.
When cooling air temperature is low, fan drive limits fan speed. High air temperature causes bimetallic coil to allow greater flow of silicone to enter drive. This increases drag between driven member and driving member, resulting in higher fan speed and increased cooling.
Scheme 1
ELECTRIC FANS
An auxiliary electric fan is used on Cherokee, Comanche and Wagoneer models with a 4.0L engine, A/C and/or heavy duty cooling system. The auxiliary fan is controlled by a relay mounted on the left inner fender panel. Engine coolant temperature is sensed by a radiator temperature switch attached to radiator outlet tank, above lower radiator hose.
When coolant temperature is more than 190°F (88°C), radiator coolant temperature switch closes to allow current to from ignition switch to flow through fan relay to ground, activating relay. When relay is activated, battery voltage is supplied to fan causing it to operate. When coolant temperature is below 190°F (88°C), radiator coolant temperature switch opens to prevent relay from being grounded and electric cooling fan from being energized.
When A/C (if equipped) is turned on, the Electronic Control Unit (ECU) grounds A/C relay coil, allowing current to flow through relay coil. This activates the A/C relay, which then supplies current to the A/C clutch, fan diode assembly and cooling fan relay, causing cooling fan relay to activate and operate fan. Whenever the A/C is used, the auxiliary electric cooling fan will operate regardless of engine coolant temperature.
Note. Cooling system must be in good condition before performing test to prevent excessively high coolant temperature condition.
- Drill a 1/8 INCH (3.18 mm) hole in top center of fan shroud. Insert a dial thermometer with an 8 INCH stem through hole in shroud. Ensure there is adequate clearance from fan blades.
- Connect a tachometer and an ignition timing light (to be used as a strobe light). Block airflow through radiator by securing a sheet of plastic in front of radiator or air conditioner condenser.
- Ensure air conditioner is turned off (if equipped). Start engine and operate at 2400 RPM with timing light aimed at fan blades. Within 10 minutes, air temperature on dial thermometer should read 190°F (88°C).
- Fan drive should engage before or at 190°F (88°C). Fan drive engagement can be distinguished by definite increase in fan drive airflow noise. Increase in fan speed can also be determined by timing light.
- When air temperature reaches 190°F (88°C), remove plastic sheet. Air temperature should drop 20°F (11°C) or more, and a definite decrease of audible fan airflow noise should be noticed. Replace fan drive if it does not function as described.
- If noise or roughness can be felt when turning fan by hand, shaft seal is leaking fluid, or fan drive is frozen. Replace fan drive.
Note. For following tests (Scheme 2)and (Scheme 3) for fan relay connector terminal and fan controls identifications, respectively.
With Air Conditioning
- If electric cooling fan does not work all the time, go to step 3). If electric cooling fan is inoperative when A/C compressor operates, start engine and turn A/C on. Disconnect fan relay connector. Fan relay is located on left inner fender panel.
- Using a voltmeter, check for voltage at fan relay connector terminal No. 2. (Scheme 2) If battery voltage does not exist, replace fan diode assembly.
- Disconnect fan relay connector. Fan relay is located on left inner fender panel. Using a jumper wire with an in-line 25-amp fuse, supply battery voltage to fan relay connector terminal No. 4.
- If fan operates, motor is okay. Go to next step. If fan motor does not operate, check continuity between fan relay connector terminal No. 4 and body ground connections. (Scheme 2)and (Scheme 3). If continuity exists, replace fan motor. If continuity does not exist, repair open and retest.
- Turn ignition switch to the RUN position. Check continuity between fan relay connector terminal No. 5 and body ground connections. If continuity does not exist, repair open circuit. If continuity exists, go to next step.
- Using a jumper wire with an in-line 25-amp fuse, jump across fan relay connector terminals No. 1 and No. 4. If fan motor operates, go to next step. If fan motor does not operate, repair fan relay fusible link.
- Check for battery voltage at fan relay connector terminal No. 2. Connect a jumper wire across radiator temperature switch connector. Radiator temperature switch is located on radiator outlet tank, above lower radiator hose. If fan does not operate, replace radiator temperature switch. If fan operates, go to next step.
- Check for battery voltage at fan relay connector terminal No. 2. If battery voltage is not present, replace fan diode assembly.
Scheme 2
Scheme 3
- Disconnect fan relay. Fan relay is mounted on left inner fender panel. Using a jumper wire with an in-line 25-amp fuse, supply battery voltage to fan relay connector terminal No. 4.
- If fan operates, motor is okay. Go to next step. If fan motor does not operate, check continuity between fan relay connector terminal No. 4 and body ground connections. If continuity exists, replace fan motor. If continuity does not exist, repair open and retest.
- With fan relay connector disconnected, turn ignition switch to the RUN position. Check continuity between fan relay connector terminal No. 5 and body ground connections. If continuity does not exist, repair open. If continuity exists, go to next step.
- Using a jumper wire with a 25-amp in-line fuse, jump across fan relay connector terminals No. 1 and No. 4. If fan motor operates, leave jumper wire connected and proceed to next step. If fan motor does not operate, repair fan relay fusible link.
- Check for battery voltage at cooling fan relay connector terminal No. 2. Connect a jumper wire across radiator coolant temperature switch connector. Radiator coolant temperature switch is located on radiator outlet tank above lower radiator hose. If fan does not operate, replace radiator coolant temperature switch.