Re: !988 4.0 litre Cherokee Aux cooling fan wiring question
 

I have an 88 MJ (Comanche) but the wiring should be the same, so I'll
post that for you.

On Sat, 2 Aug 2003 22:13:13 UTC logon@theors.net (The Or's) wrote:

> Hi there
>
> I have a 1988 JEEP Cherokee Pioneer 4.0 litre. It is an American spec
> model, first purchased in Virginia & then exported to England. It has
> aircon fitted. The chassis number is: 1JCMR7820JT050336.
>
> When I purchased the Jeep the engine auxilary electric cooling fan was
> missing. It had seized on the previous owner & he had removed it but
> not bothered replacing it. I have now bought a replacement fan but am
> having problems with the electrics, as they seem to have been
> damaged/wrongly connected by the previous owner.
>
> My questions are;
>
> 1) What colour are the two wires from the loom to the fan connector
> and where is the loom connector for the fan located?

It should be two wires to a plug that reaches pretty close to the top
of the fan: Red with White trace (hot) and Black (gnd). Both run thru
the loom to the relay panel on the left fender behind the airbox. The
relay is the forward-most relay.

> 2) What colour are the wires from the loom to the radiator temperature
> switch and where is the loom connector for the switch located?

The radiator switch is on the lower left side of the radiator (looking
forward from the cab). The wires are a Yellow from the ignition
switch that is hot (12 volts) in the RUN or START position, 0
otherwise. The other side of the switch is Gray with a White trace
which goes to the Fan Diode Assembly (2 steering diodes). The FDA has
a Green with White trace lead that goes to the fan relay coil and an
Orange lead to the A/C clutch relay.

> 3) What voltages should I expect at each of the fan relay (LHS fender)
> wire connections under the following conditions
> i) Ignition off.

0 volts on terminals except #1 - that one is hot to the battery at all
times.

> ii) Ignition on/Engine cold/aircon off

Same as i)

> iii) Ignition on/engine hot/&or airson on.

Three cases here.
a. Ignition on, engine cold: same as i)
b. Ignition on, A/C on, any temp: Terminal #2 (relay coil) will be
battery voltage - about .6 volts (1 diode drop) and Terminal #1 will
be at battery voltage.
c. Ignition on, A/C in any position, temp above (about) 210 F: same
as b.

> 4) Is there a wiring diagram available online for this vehicle
> anywhere (I have a Chiltons manual, but it does not show the
> electrical layout clearly)

Certainly. (Now I bet you want to know where <g>).

This is from the Factory Service Manual, but I'm not sure you can get
that anymore. I find the Haynes manuals to have better wiring
diagrams than Chiltons.

Test procedure: unplug the radiator temp sensor. Turn the ignition on
and short across the temp sensor plug. Fan should run with the key
on. Ignition on, turn the heater control the the defroster position
and the fan should run. The diode assy could easily be the problem
although a bad relay would be more likely, especially if the original
fan seized. In the same vein, there is a fuse wire ( Green) on the
power distribution center (on the other fender) that would likely be
blown if the old fan seized.

If it gets too grim, email me and I'll scan the FSM schematics for
you. The MJ is the same as your XJ under the hood.

--
Will Honea <whonea@codenet.net>

Re: !988 4.0 litre Cherokee Aux cooling fan wiring question
 

Hi Will

Thanks for your help.

On my Jeep the red/white & black wired connector was connected to the
radiator temperature switch! The temperature switch connector was
left disconnected. I fixed that, replaced the fusible link (which was
missing altogether) with an inline 20A fuse and was getting 12V at the
red wire into the relay (my relay has no terminal numbers, so I'll
talk in terms of wire colours). Unfortunately, I was also getting 12V
out on the red/white wire, even with the ignition off and even with
the relay removed! I traced this to the fact that the red and
red/white wires must've got so hot that the insulation had melted and
they were shorting together. I think the previous guy had tried
replacing the fusible link with a plain piece of wire, to try to get
his fan working again and in fact, in hindsight, there was some
evidence of this.

Anyway, final result is I now have a working aux fan that comes on
with the aircon. My only problem now is I'm not sure about my
radiator temp switch. I've read in some places that it should switch
the fan at 190F and others that it doesn't switch until 210F. Mine
doesn't switch at 190F and I can't get the car any hotter than 210F
exactly, even after idling for 1/2hr.

Does anybody know what resistances I should be seeing at various temps
for this switch?

Once again thanks Will.

Cheers

Darren

Re: !988 4.0 litre Cherokee Aux cooling fan wiring question
 

Sounds like you have it beat. Amazing what some people will do to
machines, isn't it?

The best test for the radiator switch is to pull the plug, short
across the wires and see if the fan comes on when the key is on. The
radiator switch is just that, a switch. It's open until the temp
exceeds about 210 (and that is really ABOUT - don't use it as a temp
guage) then it closes. If you are running with the guage in the
middle of the dial, you are in good shape. Even in 110F temps running
into a 30 mph head wind uphill (5th gear is totally useless, 4th
strains) last summer I never saw the needle past the center mark and
the fan never came on. That includes idling in traffic after a long
run with the A/C going full blast so I have no idea if mine really
works, either.

On Sun, 3 Aug 2003 20:27:30 UTC logon@theors.net (The Or's) wrote:

> Hi Will
>
> Thanks for your help.
>
> On my Jeep the red/white & black wired connector was connected to the
> radiator temperature switch! The temperature switch connector was
> left disconnected. I fixed that, replaced the fusible link (which was
> missing altogether) with an inline 20A fuse and was getting 12V at the
> red wire into the relay (my relay has no terminal numbers, so I'll
> talk in terms of wire colours). Unfortunately, I was also getting 12V
> out on the red/white wire, even with the ignition off and even with
> the relay removed! I traced this to the fact that the red and
> red/white wires must've got so hot that the insulation had melted and
> they were shorting together. I think the previous guy had tried
> replacing the fusible link with a plain piece of wire, to try to get
> his fan working again and in fact, in hindsight, there was some
> evidence of this.
>
> Anyway, final result is I now have a working aux fan that comes on
> with the aircon. My only problem now is I'm not sure about my
> radiator temp switch. I've read in some places that it should switch
> the fan at 190F and others that it doesn't switch until 210F. Mine
> doesn't switch at 190F and I can't get the car any hotter than 210F
> exactly, even after idling for 1/2hr.
>
> Does anybody know what resistances I should be seeing at various temps
> for this switch?
>
> Once again thanks Will.
>
> Cheers
>
> Darren


--
Will Honea <whonea@codenet.net>

Re: !988 4.0 litre Cherokee Aux cooling fan wiring question
 

Hi Will

My original decision to sort my aux fan out was prompted by a spell of
hot weather we had here in England. The temperature was up to 30+C
(85-90F, very hot for here!) During my 10 minute drive home from work
through moderate traffic, with my aircon running, my gauge was nearing
250F. Even without the aircon I was nudging 210F after this 10 minute
journey.

Now, with my fully working fan, the gauge doesn't even reach 190F with
the aircon running.

I guess I'm gonna call it fixed. (If the weather gets hot enough to
cause problems, then I'm probably gonna be running my aircon (& hence
my aux fan) anyway)

Thanks again for your help

Darren

Re: !988 4.0 litre Cherokee Aux cooling fan wiring question
 

On Mon, 4 Aug 2003 18:32:14 UTC logon@theors.net (The Or's) wrote:

> Hi Will
>
> My original decision to sort my aux fan out was prompted by a spell of
> hot weather we had here in England. The temperature was up to 30+C
> (85-90F, very hot for here!) During my 10 minute drive home from work
> through moderate traffic, with my aircon running, my gauge was nearing
> 250F. Even without the aircon I was nudging 210F after this 10 minute
> journey.
>
> Now, with my fully working fan, the gauge doesn't even reach 190F with
> the aircon running.
>
> I guess I'm gonna call it fixed. (If the weather gets hot enough to
> cause problems, then I'm probably gonna be running my aircon (& hence
> my aux fan) anyway)
>
> Thanks again for your help

Hmmm... Sounds like you are in the market for a thermostat in addition
to the fan! Stock thermostat is 195 F and it has to be darned near
that to get the computer in the closed loop mode. If you teeth start
to chatter on the way to work about December, keep that in mind <g>.

--
Will Honea <whonea@codenet.net>

Re: !988 4.0 litre Cherokee Aux cooling fan wiring question
 

Damn. 85-90F is called hot? When I used to go off-roading out in El Mirage (a
dry lakebed in California), 85-90F was the cool of the night 111F and up was
the norm for the day.

>Hi Will
>
>My original decision to sort my aux fan out was prompted by a spell of
>hot weather we had here in England. The temperature was up to 30+C
>(85-90F, very hot for here!) During my 10 minute drive home from work
>through moderate traffic, with my aircon running, my gauge was nearing
>250F. Even without the aircon I was nudging 210F after this 10 minute
>journey.


-Bill (remove "botizer" to reply via email)