Radiator fan won't turn off

[exranger06]

1992 Honda Accord-
I just got the car back from the body shop, so I haven't really driven it in about 2 months. However, upon bringing it home, the fan would not shut off. I realize the fan sometimes runs after the ignition is turned off, but I just hooked the battery back up this morning after the car has sat all night and the fans turned back on for no reason. It is definitely NOT because the engine is hot.

What I've done so far: replaced coolant temp sensor. Did not fix the problem. (Actually, I didn't install it. I just plugged the harness into the new sensor and the fans immediately turned on.)
Swapped cooling fan relay with another one. Did not fix anything.

What else I've noticed: If I turn the ignition on so all the dash lights turn on, the fans stop. As soon as I turn the ignition off, the fans turn on again.

 

[exranger06]

It seems there are several different part numbers for the coolant temp sensor. I have a feeling I may have gotten the wrong one, even though it plugged into the harness no problem. I'll have to ordera different one and wait at least until Monday to get it.

Some other info worth sharing: If I unplug the harness from the sensor, the fan turns off. It only turns on with it plugged in, or if I short the terminals with a paper clip.

 

[SwampSurvivor]

If the ignition is off, it's probably not the coolant temp sensor. Start by checking the relays and wiring.

 

[exranger06]

Well, I'm not sure it's actually a "coolant temp sensor." These different part numbers are actually called different things, even though they all have the same connector and look extremely similar. The other part number I found that I think is the correct part is the "cooling fan switch." It's located on the thermostat housing right where the upper rad hose goes to the engine.

 

[HerrStig]

It would help to take some voltage readings, keep in mind most of these circuits are "failsafe" and will keep the fans ON if a componet quits, rather than burning your engine up because they DIDN'T kick on when they should have. The relay that feeds the fans is kept OFF by the presence of voltage on the coil, to turn ON the fans, voltage is REMOVED from the coil. That way if there is a failure in the sensor circuit it will keep the fans ON.

 

[LeakySeals]

Could be radiator fan relay or the thermo switch.

 

[mechtech2]

You may have replaced the wrong sensor.
Often there are sensors that are separate for the fan and computer.
If it works/doesn't by unplugging it, that is a strong clue to me.
And did you replace the right relay?

 

[Nukeman7]

Originally Posted By: exranger06
Well, I'm not sure it's actually a "coolant temp sensor." These different part numbers are actually called different things, even though they all have the same connector and look extremely similar. The other part number I found that I think is the correct part is the "cooling fan switch." It's located on the thermostat housing right where the upper rad hose goes to the engine.

Yep...this is the correct part:

Fan Switch

It is a switch, not a temperature "sensor".

 

[The_Jeff]

You need to ohm out your new sensor, if it is zero or infinite it's a switch. If you get some ohms it's a temp sensor.

I'm seeing sensors for "with gauge" or "with (overheat) light" as well. You could potentially have three: one for the fan relay, one for the computer, and one for the gauge!

Was the plastic connector on your old or new part the same color? Was the old one a unique color?

 

[Smoky14]

Murphys law #2: he who screwed with it last screwed it up.

What did the body shop do? I'd start looking there.

YMMV

 

[exranger06]

Originally Posted By: eljefino
You need to ohm out your new sensor, if it is zero or infinite it's a switch. If you get some ohms it's a temp sensor.

I'm seeing sensors for "with gauge" or "with (overheat) light" as well. You could potentially have three: one for the fan relay, one for the computer, and one for the gauge!

Was the plastic connector on your old or new part the same color? Was the old one a unique color?

The hew sensor had a black connector. The old one I think was a gray or green color. The new one I ordered is a grayish color. It won't be in until Tuesday.

I'm 99% sure the switch is the problem and that I got the wrong one. I'm also 99% sure this new one I ordered is the correct one and should fix my problem Will keep everyone updated.

 

[exranger06]

Got the new (correct) switch installed. The first one I got was definitely not the right one. I hadn't realized it didn't even have the right thread size.

The fan now stays off as it should. I still haven't driven it yet, though; I need to replace a battery cable and get a new battery. The real test will be seeing if the fan turns ON when it should. I'll be keeping a close eye on the temp gauge when I finally take it out.