Other ideas on cooling...

[Sarge]

I do believe that your auxiliary fan doesn't work because your AC is discharged.

Odd. My 1993's AC was "removed" when my daughter took out a tree and a fence but the aux fan still works great.

Sarge

 

[sjx40250]

Fishburn, The diod is in the wire harness down by the front of the air box. It is a goofy looking thing that is not "serviceable". I tried to get a replacement and was told that I needed a new harnesss! The only way to replace it, it will come out of the holder, is to get one at the yard.

Sarge, 91 and newer have different cooling sensor configuration. The fan is turned on buy the ECU, IIANM, and the sensor is on the thermostat housing. That sensor is not an off/on switch but varies resistance with water temp. That is why the aux fan still works without the A/C.

 

[fishbum]

thanks - at least I can "prick" the wires and see if the voltages are right....

 

[Fred]

Just an update. After replacing the radiator on the 88 MJ with a two row closed system from Performance Radiator, the temperature never went high enough to turn on the auxiliary fan, and turning on the AC did not turn on the auxiliary fan. The AC was discharged, and the clutch for the compressor was disabled by a low pressure cutoff. I finally charged the system with a 134a conversion kit, and the auxiliary fan did activate when the compressor clutch kicked in. The auxiliary fan is activated to draw air over the condenser when the air conditioner is on, not as an aid to cooling, although it does that as an aside.

The conversion kit seems to work fine. I did learn that the valves on the compressor are rightey loosey, lefty tighty, and I had to turn the low pressure input on the compressor which took a 1 1/8 inch wrench, also the apparent schrader valve on the adapter does NOT prevent leakage of the gas. :dunce:

Even with low gas, it seems to work well.

Fred

 

[skipc]

Check the relay, which may not be energizing because of the AC, but mine went bad and I had the same problem. The diode block IS removable (on my 89) - just wiggle it out of its little socket. It's small, so you can miss it. I almost thought mine was bad, but it tested OK. I was going to make a replacement with 2 RadioShack power diodes and splice them in if bad. Then I thought it was the socket because I could tap/wiggle the relay and it worked. Cleaned it up and it lasted a few days, then the relay went bad permanently. Replaced it with a generic "Bosch type" and runs fine ever since.

The better option might be to run a wire from the switched 12v bus through a toggle switch inside the car, to another relay with the contacts in parallel with the fan relay. Then you have a fan that runs all the time, but you can turn it off when you want.

I never get in weather cold enough to even run a heater - fans are good ;-)

 

[fishbum]

Ok, it turns out that my system is now running well enough that it never got hot enought to turn on the aux fan - EXCELLENT!

I towed my boat for a test ride to see if the engine got hot, and it stayed rock solid at about 212 degrees, so we went to the launch... Parked the XJ idling while waiting for the ramp to clear, and when I came back the aux fan was whirring away! Very Cool!!! (no pun)

The fan would not turn on with the A/C switched on because it was discharged, and I took the cooler off the vehicle.

Final analysis: Removing the A/C cooler from in front of the radiator dropped the temp 5 degrees. New OEM thermostat dropped the temp another 10 degrees so now I'm running consistently just slightly above 210. It's a little cooler today (60F), so when driving to work the gauge sat right on 210.

At least I can relax knowing the cooling system is now in good shape and I can safely tow with the added tranny cooler.

thanks to everyone for all their help and suggestions. Debugging these systems is not the simplest task with so many variables to consider....