Cooling Fan Dilemma

I've been dealing with a small cooling fan problem and have been getting help at jeep forum, but i thought i would throw this up here to see if anyone here has ideas....

The facts...
98 Cherokee 4.0 with a/c

Problem: overheating randomly in heavy traffic in hot weather, pretty sure its only with a/c engaged

What i can test:
-fan is working when current is applied from battery to it and will run with no problems...ran 10 minutes

-ac works and blows cold air, but compressor engages and disengages at its own leisure fan does the same in conjunction with the a/c clutch on and off

-temp gauge works

-when temp reaches 210 aux fan shuts off completley and will not come on with a/c or at all...(this is when it is supposed to be continous)...however it took me a while to get to this point so this has only been tested once. this would explain though that the temp will take a long time to get to 210, but takes very little time to over heat once this temp is exceeded

is this a phantom problem, or does a real solution exist short of installing a manual override. i have no problems wiring, as a theatre electrician, however if anyone has a schematic or easy tips it would be appreciated.

Possible relay?

Dumb question, but bears asking. How old is the fan clutch?

The E-fan isn't enough of an air mover to keep the engine cool by itself. The mechanical fan can kinda keep the engine cool lone-handed, but needs help from the E-fan from time to time. The aircon is supposed to kick the E-fan on when active, since the aircon puts an extra load on the engine (especially at idle) and an extra thermal load on the cooling system (since the condenser is right in front of the radiator.)

Typical service life of the fan clutch in an XJ seems to be 4-5 years, after which the silicone fluid that allows the clutch action loses its body and shears more than it should.

This can be checked with a hair dryer, or by letting the engine idle (hood closed) for 7-10 minutes. Once the fan clutch is heated up and the engine OFF, you should have a difficult time turning the fan blades by hand. If it's easy, and the body of the fan clutch is hot, replace the thing.

I find it helpful to write the date of replacement on a flat spot with a Sharpie pen for future reference when I replace it.

i'm pretty sure the fan clutch needs replaced since i've had the jeep for 4 years and haven't done it...could it be that the engaging and disengaging is doing something to the relay causing it to fault, or is there a problem at the ecm when it tries to engage the fan at 210?

So you're saying the efan works below 210 but it doesn't above 210?

You may want to test the relay as well (they're cheap enough - "test by substitution,") but yes, replace the fan clutch before too long. I'd not be terribly surprised if that solved an awful lot of your problem.

The relay should be either a standard DIN (about 1" cube) or a Mini-DIN (about 1"x1"x1/2"). The DIN relays are easier to find - I may start carrying Mini-DIN relays for projects and spares for people.

You're a 1998, which is OBD-II. That means that all functions for engine coolant temperature (gage, ECU driver, E-fan) are driven by a single temperature sensor. Does your gage work? If it does, then your sensor should still be good.

You should have spare relays in your spares box anyhow (along with fuses, lamp bulbs, ...) so you can test that by substitution.

Some of those e-fans don't kick on til 220*--has it gotten that high?

it got up above 220...i didn't want to let her get too hot and i was tired, so i shut her down...i'm actually going to have to drive her tomorrow, i may stop a few times to check it out. i may have to pick up a spare relay before work tonight...ugh working a double shift was a bad idea today