Electric Fan...

I seem to be having trouble with my electric fan. I won't come on when it needs to. I am not against wiring a switch but would like to trouble shoot the problem first. I need to know a couple of things first. I have the schematic so tracing the gripe should be easy.

1. Cooling fan relay location?
2. Fan diode assembly location?

Pretty certain I know where the radiator temp switch is.

Any other thoughts from the pros would be appreciated.

It is an 87 4.0 Auto 4wd (Laredo model if that is a any relevance)

8700XJS

Looked up locations for you. The relay is located on the left (drivers) inner fender in the engine compartment. The fan diode assembly is in the wiring harness from the relay to the fan on just down from the relay. I would first jump 12 volts directly to the fan (yellow tan wire)from the battery (using a 30 amp fused lead) repeatadly to see if the fan motor has a dead spot. If it does o.k. after 30 times or so I would then check to ensure that the relay is recieving signal. using a digital volt meter or a test light check that the orange wire is providing 12 volts to turn the relay on and that the black wire has a good ground. If that is good check for voltage out of the red tan wire of the relay. This wire turns to yellow tan before it gets to the fan. If you do not have 12 volts that means the relay is bad. If you do not then either the diode assembly is bad or the temp switch is not functioning. You can test coolant sensor by geting the temp of your engine to 230 degrees and testing for voltage on the grey wire. If you have voltage on the grey wire it is o.k. if not replace the switch. If you have voltage to from the switch to the diode but no vlotag out of the diode the replace the diode. The red wire that goes to the relay is the supply voltage for the fan. There is a green fusable link on that wire that may be damaged it would hurt to check that either. I myself would bet on the fan itself or the relay. Good luck. any more questions just enquire.

Joe

Definately check the wiring. An easy way to check the system is to just jump the 2 wired that go the the fan switch on the drivers side of the radiator. The most common problem I have seen is that the radiator is slightly restricted. Since the fan senses the temp of the coolant after it has passed through the radiator, the restriction is causing the coolant move slower and has more time to cool down. Feel around the radiator when then engine is fully warmed up and check for any cold spots. This will indicate where the restiction may or may not be.

Bryan

SOOLONG said:

Looked up locations for you. The relay is located on the left (drivers) inner fender in the engine compartment. The fan diode assembly is in the wiring harness from the relay to the fan on just down from the relay. I would first jump 12 volts directly to the fan (yellow tan wire)from the battery (using a 30 amp fused lead) repeatadly to see if the fan motor has a dead spot. If it does o.k. after 30 times or so I would then check to ensure that the relay is recieving signal. using a digital volt meter or a test light check that the orange wire is providing 12 volts to turn the relay on and that the black wire has a good ground. If that is good check for voltage out of the red tan wire of the relay. This wire turns to yellow tan before it gets to the fan. If you do not have 12 volts that means the relay is bad. If you do not then either the diode assembly is bad or the temp switch is not functioning. You can test coolant sensor by geting the temp of your engine to 230 degrees and testing for voltage on the grey wire. If you have voltage on the grey wire it is o.k. if not replace the switch. If you have voltage to from the switch to the diode but no vlotag out of the diode the replace the diode. The red wire that goes to the relay is the supply voltage for the fan. There is a green fusable link on that wire that may be damaged it would hurt to check that either. I myself would bet on the fan itself or the relay. Good luck. any more questions just enquire.
Joe

Click to expand...

Ok I am getting the 12 volts to the relay and 12 volts out of the relay when the AC is on. On the red and white wire. The aux fan also turns on when the AC is on. I switched the relay with my O2 relay since they are the same relay. I am not getting 12 volts at the orange wire. I jumped the fan to the battery with my meter leads and the fan runs fine. Doesn't look like there are any bad spots in the fan. After looking at my schematic it seems to me that the diode and relay are good. The switch is either bad or there is a bubble. I have seen alot about bubbles in the old system but one thing that is not clear to me is if I have good water flow could there still be a bubble? My temp goes up but not to the red and when the thermostat opens it drops back down to around 180 it then goes back up and back down. It does this until I have driving around for a while eventually it barely goes down below 210 so I would say normal driving temp for me is 210-220. I have replaced my temp sending unit to the gauge, Radiator (triple core), water pump, t-stat, bottle (yesterday), and the heater control valve. All of this has been with in the last year.

I would like to hear your thoughts on the fan working with the AC and not by itself? Are my conclusions correct about the diode and relay? If I need to check my diode so be it. Is it the little orange plastic thing sticking out ot the wire bundle in that area? If it is and I am going to check it, how do you get it apart to check it? I have never had to take one of those things apart.


Thanks,
8700XJS

Bryan C. said:

Definately check the wiring. An easy way to check the system is to just jump the 2 wired that go the the fan switch on the drivers side of the radiator. The most common problem I have seen is that the radiator is slightly restricted. Since the fan senses the temp of the coolant after it has passed through the radiator, the restriction is causing the coolant move slower and has more time to cool down. Feel around the radiator when then engine is fully warmed up and check for any cold spots. This will indicate where the restiction may or may not be.

Bryan

Click to expand...

I felt around as much as I could and there were no spots that felt hotter or cooler than another. I also gave the upper rad hose a little squeezing and I could hear and see water going into the bottle. I then did the same thing to the lower rad hose and got the same result. When I squeezed the upper hose I grabbed the lower hose and could feel the pressure changes with every squeeze. I did the same thing again in reverse and could feel the pressure from the lower hose to the upper hose. Not sure what I am trying to say other than I don't believe my new radiator to be clogged.

8700XJS

If you have a new radiator then I would say it is good. Did you replace the fan control switch in the radiator? I posted before about just jumping the 2 wires that go to the fan switch. Did the fan turn on when you did this? If all the wiring checks out, I would suspect a bad fan control switch.

Bryan

The fan "sensor" in the driver's side radiator tank is nothing but an ON/OFF switch. Disconnect it from the wiring harness, connect your multimeter, let the Jeep idle for awhile and see if the switch closes. If necessary, block off the grille with a blanket or something to make the cooling system heat up faster.

What temperature thermostat do you run? The aux fan is supposed to turn on at something like 217 degrees, I think. If you run a cold t-stat maybe you're not reaching the activation point.

I've lost a couple of these switches, so I just end up wiring in a toggle switch in parallel with the thermal switch in the radiator. Even when you replace the switch, you will still have the ability to override the system and turn the fan on at will.

The aircon will trip a separate signal to the fan relay, so it is correct for the fan to come on when the aircon is turned on. There are two signals for the auxiliary fan - the thermal switch and the aircon fan signal.

The easy way to add the override switch is to run both wires to a toggle switch on the panel in a convenient location. I've actually got my hands on some OEM switches, and installed one in a blank location for the bypass switch.

5-90

Eagle said:

The fan "sensor" in the driver's side radiator tank is nothing but an ON/OFF switch. Disconnect it from the wiring harness, connect your multimeter, let the Jeep idle for awhile and see if the switch closes. If necessary, block off the grille with a blanket or something to make the cooling system heat up faster.

What temperature thermostat do you run? The aux fan is supposed to turn on at something like 217 degrees, I think. If you run a cold t-stat maybe you're not reaching the activation point.

Click to expand...

Eagle I did in fact let it heat up as much as I thought it would take to open the switch. It was definitely higher than it used to be for the fan to come on.

I am running the 195t-stat. I have to admit I am not exactly sure when the fan quit. I chanaged my radiator. Then I changed the sending unit to the gauge because mine would start out showing about 140 degrees when dead cold. Shortly thereafter I changed my cluster for one with a tach.


Bryan C. I did not jump the connector yet to see if the fan turns on. I will do that today.

Bryan C. said:

... Did you replace the fan control switch in the radiator? I posted before about just jumping the 2 wires that go to the fan switch. Did the fan turn on when you did this?...

Bryan

Click to expand...

OK I did not replace the switch when I did the radiator. Should have.

The fan did turn on when I jumped the connector. Time for a new switch.

5-90: I would like to put a switch in and am thinking about using my rear defrost switch. I live in the desert and don't really need it more than twice a year. I have all four of the switch locations filled in my XJ.

I want to thank everyone for the replies.

8700XJS

The rear defog switch is a "momentary" type, so it would be a little more work. If you can get a regular "on-off" type (like for the OEM driving lights or perhaps the rear windscreen wiper) you will save some componentry and work for yourself.

If you use the rear defog switch, you will need to cook up a "latching" relay ckt that will "make" when you push the switch up, and "break" when you push the switch down. It's doable, but I don't remember how offhand (although I'm sure someone else here does...)

5-90

5-90 said:

The rear defog switch is a "momentary" type, so it would be a little more work. If you can get a regular "on-off" type (like for the OEM driving lights or perhaps the rear windscreen wiper) you will save some componentry and work for yourself.

If you use the rear defog switch, you will need to cook up a "latching" relay ckt that will "make" when you push the switch up, and "break" when you push the switch down. It's doable, but I don't remember how offhand (although I'm sure someone else here does...)

5-90

Click to expand...

Ya know I forgot about that. I could just got radio shack or the Zone and get a nice switch and use it. One thing I did think of doing was getting an old floor mount bright switch and using that. Anyways I will come up with something cool.

8700XJS