Aux. Cooling Fan Not working?

[bremery88]

I have a 1988 Cherokee with the 4.0 inline six. I have a stock auxillary a/c cooling fan that will not turn on. It just stopped working. The fan unit works (I hotwired it), and I replaced the thermosat. I looked for the relay and replaced the one right near the windshield washer tank on the driver's side.

was this the right one? Are there fuses and circuit breakers that I can check? (All the fuses under the dash look great)

Also is there a way to test the sensor in the radiator with a V.O.M.? or I need to pull it?

Any info will be appreciated.
-Brandon

 

[savin]

I just went through this samething on my 88. There is a temp switch in the radiator. It's on the drivers side below the hose outlet. I bet this is your problem. It's a pain in the a$$ to get to, unless you remove the radiator or air cleaner box. The worst thing, if you opt to remove the radiator, is to get all the air pockets out of the heating system so that it will still flow. Good Luck :roll:

 

[XJNick]

Hi,

Ok Let's take a step backwards here...

Does the fan run while the A/C is on? Keep in mind this fan should be running ANYTIME the A/C is on. It should NOT run with the A/C OFF under normal engine temperatures. Instead, the fan is designed to kick-in only if the engine is beginning to overheat (greater than 230 degrees i think).

The Aux. Fan is NOT run through any fuses or circuit breakers, but instead pulls its power through a fuseable link by the starter relay. It is doubtful that the link went bad unless the motor shorted out.

More likely, would be that either the fan relay went out (I believe this relay is on the driver's side fender by the air-box). Another possibility is that the fan's DIODE trio burnt up. This assembly of diodes is located in a tiny orange box with three wires attached. This assembly can be found near the airbox and close to the fan it self.

You can test the relay with a voltmeter, and the Diode assembly with a Multimeter that's set to measure resistance.

Good Luck :mrgreen:
-Nick :!:

 

[bremery88]

I replaced the relay and ran the A/C and the fan did not come on. I could not see the diode trio, but I will look again. Thanks for the suggestions.

-Brandon

 

[savin]

With the engine off but the ignition on, unplug the connector to the switch in the radiator and short them out with a short wire. If you here a clicking sound but the fan does not come on, that means you have power to the relay but not to the fan. If you here nothing, the whole system has no power and you will have to trace out why. If you need the wiring diagram, let me know and I will e-mail you a copy. If the fan comes on, replace the temp switch in the radiator.

 

[bremery88]

The new radiator switch did not work. I can not get the fan to come on. I believe I have some air in the system, so I bleed the system multiple times. The jeep is not over heating, but is running at 210. I know this is normal, but it ran a lot cooler before, because I took out the A/C condenser. (The fan worked after I did this).

I am not sure what to check next.

-Brandon

 

[XJNick]

Hi,

You need to check each post of the Fan Relay with a voltmeter to find which have voltage and which don't. Doing so will greatly help you determine the cause of the non-working fan.

The Relay pin-out is as follows:

#30 = Constant Hot power from fuseable link
#87 = Hot output to fan motor (switched by relay)
#87a = Not used
#85 = Hot Trigger signal from heat switch or A/C switch (activates the relay)
#86 = Chassis Ground

If you have no power at terminal #30, suspect a bad fuseable link.
If you have no power at terminal #85, suspect bad heat switch, bad A/C clutch relay, bad diode assembly, or loss of power from ignition switch.
If you have no power at terminal #87, suspect a loss of power to terminal #85 or a bad radiator motor relay.

Hope that helps :mrgreen:
-Nick :!: