Stock electric fan question.

Well start with my first question:

My electric fan doesnt work, If I jump the relay it does work. Checked the sensor and when the rig is hot (above 220) the sensor isnt closing. So I assume that it is bad.

So I went into my Chilton books and if the AC compressor doesnt work, the electric fan wont work. I turn on my AC and no AC compressor, cold ac, or electric fan. I check the relay for the AC compressor and im getting a tiny bit of voltage. (Under a volt) so I would say that was a bad connection somewhere. A really bad one at that.

Id like to know what connections I should check for the AC compressor relay.

My second question is what would the coolant temp sensor cost? And if I dont replace it and just run a switch to the aux fan will there be any reprocussions?

First question....what year/engine?

Whoops, used to having a sig.

1990 with 4.0

I just went through the same thing with my 90, no fan or A/C clutch and low voltage at the relay. Found my problem was a loose connection at the climate control switch, guess I knocked it loose when I replaced the stock radio with my CD player.

summitlt said:

Well start with my first question:

My electric fan doesnt work, If I jump the relay it does work. Checked the sensor and when the rig is hot (above 220) the sensor isnt closing. So I assume that it is bad.

So I went into my Chilton books and if the AC compressor doesnt work, the electric fan wont work. I turn on my AC and no AC compressor, cold ac, or electric fan. I check the relay for the AC compressor and im getting a tiny bit of voltage. (Under a volt) so I would say that was a bad connection somewhere. A really bad one at that.

Id like to know what connections I should check for the AC compressor relay.

My second question is what would the coolant temp sensor cost? And if I dont replace it and just run a switch to the aux fan will there be any reprocussions?

Click to expand...

Sounds to me like you have two problems.
1. A/C needs charged, that's why it don't turn the compressor on.
the A/C test is used because it bypass's the fan switch.
2. Your Fan switch is bad, you could put a toggle switch on it if you don't use the A/C.
A new fan switch is about $20.00

Where is the eye to see if it is "full" or not. I looked around but didnt seem to see anything.

summitlt said:

Where is the eye to see if it is "full" or not. I looked around but didnt seem to see anything.

Click to expand...

You need to check the pressure to tell if it needs charged.
Some systems have the full window but that only works when the compressor is running.

If I remember right there's a can down by the framrail on the passenger side by the front of the block. This is should have a sight glass on top of it to check the AC level.

There is also the electrical connector to the low pressure AC protection switch at the same spot. This keeps the AC compressor from running without freon and oil to prevent the AC compressor from killing itself. For a quick test you can briefly jumper the two terminals of the connector together.

ON my 88 XJ the fan is turned on two ways, it should be the same on your 90. The first is when the AC clutch engages the fan runs, the second way is when the temp sensor in the radiator reaches 190F. Either "signal" comes to a diode pack and then the current goes to the fan relay to engage the electric fan.

The sensor is located in the raditor tank on the driver's side. I will call it the cold tank. It that hex thing between the trans cooler line attachements to the radiator. When the temp of the coolant reaches 190F in that cold tank the switch closes. When the switch closes the relay will engage to run the electric fan.

You may want to make sure the sensor in the radiator is plugged into the chassis harness. If you find the sensor plugged in then you can do a test. With everything off you can jumper the pins in the chassis harness for the switch, turn on the igniton and see if the fan runs. I think it will run even if the engine not running if the ignition is ON. If the fan runs then you know the radiator sensor part of the fan harness is good.

I do not know of a good way to test the switch in the raditor, removing the switch is the only way to test it. This means you will have to drain the coolant out of the radiator.

To test the switch stick it in a pot of water so the portion of the switch in the tank is covered by water, do not fully immerse the switch in water. Then heat the water and wait until the switch closes. You should have a thermometer in the pan and an ohm meter to let you know when the switch closes and the thermometer will tell you the temp. If it 190 it good. My guess is the range is 185-195F. I will have to check my manuals to make sure the temp value is correct.

When I changed my radiator last year I installed a new temp switch instead of recycling my old switch. Made the job go quicker by having the sensor already installed in the new radiator.

You may have a working switch, just your radiator is cooling the coolant enough so it does not switch on the fan. How old is your radiator? Maybe you need to do a replacement, it may be partially stopped up. You could have a lower radiator hose sucking shut if it lacks an internal spring. Could be several things.

I know the sensor is bad, at high temps, (almsot to the "red Zone) it still doesnt close, so im pretty sure its bad.

summitlt said:

I know the sensor is bad, at high temps, (almsot to the "red Zone) it still doesnt close, so im pretty sure its bad.

Click to expand...

Not necessarily so, low flow through the radiator will cause the water to be cool in the radiator tank, even though the engine is hot.