Aux fan won't turn on (I've tested & searched)

[fiatslug87]

'89 2WD MJ, 4.0, AW4, without AC

I've tested the Cooling Fan Relay according to the FSM:
Continuity between terminal 5 and ground - continuity OK
Jumped terminals 1 and 4 - fan operated
Checked voltage at terminal 2 with 1 & 4 jumped - 0.13 volts (my '90 had similar voltage and it works properly)
Jumped the radiator fan switch harness connector – fan operated
Checked continuity of cold radiator fan switch – no continuity (expected)
Checked continuity of hot radiator fan switch – no continuity ==> Bad switch
Replaced with new one, checked its continuity when hot - continuity OK
BUT fan still won’t turn on even at >240°

Swapped the relay with the one from my '90 - fan didn't operate

If I jump the harness connectors I can get it to run so maybe I’ll hook up a manual switch as a last resort but I’d rather not.

Any ideas? :repair:

 

[summitlt]

No ideas, but I did a manual switch on mine and have no problems. Just have to remember to turn it on in the city. I used a factory fog light switch, so it looks facotry and the light comes on telling me its on.

 

[MJmk]

By unplugging the radiator switch, jumping it, and having the fan operate, you have eliminated a problem with anything up to that point. All that is left is the possibility of a bad connection where the radiator switch plugs into the harness, or the switch itself (unlikely since you replaced it), or the hot coolant isn't circulating to the switch to close it. Any chance you got a stuck thermostat? Does the radiator get hot?

A friend of mine has a '89 MJ he bought new, 4.0L, no a/c with the standard cooling system, and it does not even have the aux. fan!

 

[Lou]

I don't have an FSM for the '89, and given the inconsistency of Jeep's relay number scheme, and I'm looking at a Chilton schematic for a 87-88............but, isn't there suppose to be 12V on the number 2 pin(red wire) that is fed through a fusible link.

If so, you should have 12V not 0.13V.

 

[fiatslug87]

Re: Aux fan won't turn on (I've tested & searched) Eagle?

possibility of a bad connection where the radiator switch plugs into the harness

I thought of a bad connection at the switch/harness so I cleaned the harness connector and crimped them slightly to provide a tighter fit but that didn't help.

the switch itself (unlikely since you replaced it), or the hot coolant isn't circulating to the switch to close it.

Since the new switch shows good connectivity when the engine is hot (and open when cold), I have to assume the hot coolant is hitting it.

Any chance you got a stuck thermostat? Does the radiator get hot?

I'm pretty sure the thermostat is working; the temp rises to ~ 210-220 then drops to 210 as the thermostat opens. The radiator seems to heat up.

The temperature only gets too high if I sit in traffic and drops as I start moving (fan clutch?). I revved it at ~2500 in the driveway to get the temp up to see if the auxiliary fan started, but it never did, that's what started this whole saga.

 

[fiatslug87]

I don't have an FSM for the '89, and given the inconsistency of Jeep's relay number scheme, and I'm looking at a Chilton schematic for a 87-88............but, isn't there suppose to be 12V on the number 2 pin(red wire) that is fed through a fusible link.

If so, you should have 12V not 0.13V.

I too was concerned about this, the FSM (it's for a '90) doesn't say what the voltage should be (in fact it says to continue to step "f" but there isn't one) that's why I tested my '90MJ and it too was low. Where is the fusible link and how can I test it? Thanks.

 

[MJmk]

:laugh3: I must be missing something here! If you unplug the radiator switch from the harness, jump across the harness terminals, the relay closes and the fan comes on every time? If that's the case, seems like it has to be the switch, or the coolant in the switch side of the radiator isn't getting above 190' to close the switch!

 

[treedoc]

i put a switch on mine last year, love it.