rok-jeep

So I'm at a loss. The aux. electric fan on my 1998 XJ is not working. I got a new relay and put that in...nothing. I checked the 40amp fuse in the distribution block....its fine. I connected the fan to the battery with some wire and the fan works that way.....so the motor is good.

The temp gauge has been acting funny the last few years. When crawling it would climb to 220* then jump to 260* but nothing would be boiling over and the overflow bottle is not full. If I rev up the engine for a while it will eventually drop back down to 220*. This started a few years ago but would only happen once or twice a summer. But last year it was rather frequent like once or twice a trip. For example, I couldn't get through the Box on the Con without it happening.

I thought it was strange the overflow bottle was empty when I started looking at it but its been dry since I got the jeep 7 years ago. I never thought anything of it but I have since topped it off to the full mark. There is no coolant in the oil, I checked that too.

Last summer I put on a new thermostat, fan clutch, water pump and flushed the radiator with water. Then refilled the system with the heater running on high. Temp gauge still did the same thing.

I'm wondering if there is an air pocket getting trapped in the thermostat housing causing the temp to spike up?

I put in a new temp sensor yesterday thinking that would help. I didn't have time to get the jeep to operating temp when running but the the fan will not kick on when I turn on the AC like it should. Very strange.

Any other ideas? I'm going to try to get the Jeep to operating temp today and see if that does anything.

Relay-good
fuse-good
fan motor-good


I'm at a loss right now.

Firestorm500

It's not an air bubble.

It may be the dedicated temperature sensor for the fan.

SeriousOffroad

Does the fan come on when you turn on your Defrost or A/C?
Have you tried disconnecting the connector at the water temp sensor and starting the engine?

djb383

The coolant recovery bottle MUST always have coolant in it. If it doesn't, air is drawn into the radiator when the motor is cools. Coolant level in the bottle should fluctuate between the upper/lower marks.....motor hot/cold. Radiator cap is the key to the system and must function properly. Sounds like it may be time for a new radiator.

freegdr

this done yet? if ac compressor does not kick on fan will not either...

CCKen

Here's some info I put together concerning the radiator fan operation. You may want to read through it and see if it makes sense to you.



Did you check the fan relay coil fuse in the Junction Block? Here's a pic that shows its location.



Here's a pic showing the AC pressure switches being jumpered. I used a paperclip (real technical - LOL)





Here's a pic of the 470 Ohm resistor jumping the ECT sensor connector.

rok-jeep

In the junction block on the kick panel in my 1998, fuse #10 is empty and shows "empty" in the manual. I couldn't find any other "fan coil relay" fuse anywhere listed in the manual. That info must be for an earlier jeep.

yarom

Lucky you. Mine has never stopped working since day one. Very noisy.

It has been on as long as the car is on - always. I have never seen it shut down, ever...

CCKen

Sorry about that. It's for a '99 XJ. The '97, and presumably the '98, use fuse 11, 20A, for the fan relay. It's the next one down from the red 15 Amp fuse. However, I don't think it's blown because it also powers the ASD relay, Fuel Pump relay, and a whole bunch of other goodies.

CCKen

If you tried the connector jumping shown in post #6 and the fan still won't turn on, it may be an open in the ground wire from the PCM to the fan relay coil. The fan relay coil is powered through the start-run bus fuse (11 in your case) at relay socket #86. THe PCM provides a ground to this coil at relay socket #85. When the PCM receives an AC select signal or a high coolant temp signal it will provide a ground to the coil, pulling the relay contacts closed and proving power, from the 40 Amp fuse, to the fan.

If the PCM ground wire (C27 18 DB/PK) from pin C2 of PCM connector C3) is open, no ground will be provided to the fan relay coil.

Here's a pic of the relay socket configuration:



Check these pin numbers against the pin numbers on the bottom of your fan relay to confirm this is the type relay you have.

To troubleshoot an open in the PCM ground wire you'll need to detach PCM connector C3, remove the fan relay, and using an Ohmmeter, read between relay socket 85 and PCM C3 socket C2. You should read continuity.

Here's C3. Disregard the darkened pins, that was for a different problem. If this is not your C3 pin configuration let me know. Shown is a '99 C3 pinout. The '97 ('98?) C3 pinout is the same, as far as the cavity (CAV)numbering list goes, but it the illustration of the connector cavity numbering is different. A Chrysler thing I guess. You're looking for an 18 Ga. Dark Blue/Pink wire.

djb383

Sorry for the hi-jack but, if I'm understanding correct, the compressor and efan will not engage when ambient below freezing is sensed?

CCKen

Correct.

Per the FSM:

The low pressure cycling clutch switch contacts are
open when the suction pressure is approximately 141
kPa (20.5 psi) or lower. The switch contacts will close
when the suction pressure rises to approximately 234
to 262 kPa (34 to 38 psi) or above. Lower ambient
temperatures, below approximately -1° C (30° F), will
also cause the switch contacts to open. This is due to
the pressure/temperature relationship of the refrigerant
in the system.

SeriousOffroad

Incorrect.
The fan will come on passed on the temperature of the coolant 9213deg f. or greater) or if the pressure in the A/C system are such that they cause the contacts in the pressure switches to remain in the closed position.

Ambient temperatures are not measured by the PCM with regards to A/c compressor operation. Low ambient temperatures will cause the fan to cycle on an off only because of the effect that cold air has on the refrigerant passing through the condensor coil. the fan will cycle off to allow the hi-side pressure to rise so that adequate head pressure is achieved, this allows for an acceptable pressure drop as the refrigerant passes from the high side of the system to the low pressure side of the system.

DFlintstone

It had seemed to me you guys are saying about the same thing.

Ambient temperatures are not measured by the PCM with regards to A/c compressor operation. Low ambient temperatures will cause the fan to cycle on an off only because of the effect that cold air has on the refrigerant

And;
contacts to open. This is due to
the pressure/temperature relationship of the refrigerant
in the system.

True, temperature isn't what makes mercury rise in a thermometer, it's actually the pressure that does it.

Or maybe I'm completely missing something. Anyway I just wanted to chime in and thank Ken for helping clarify the SPDT, (Single Pole, Double Throw), relay where all the action converges. At that socket you can, *Power the fan directly, *check for power to both the fan, and the relay coil, *and check that the PCM is grounding the relay to activate the fan.

djb383

I'm totally confused now.