Quick bypass switch for stock aux. electric fan

Credit for this quick fix goes to Bob Loose (BLoose) for this one!

My '96 was having an overheating issue and I needed to provide more air to the radiator but simply clicking the A/C on would only keep the fan on while the compressor cycled. I knew I could "hot wire" the fan to run off the battery, but I hate cutting into the factory harness. '96 OBDII also doesn't like it when you simply ground out the sensor lead... this is where Bob comes in....

While on the trail, he bent up a piece of stiff wire to jump the power terminals to the fan relay in the fuse box. That worked, but the wire gets hot and not easy to pull out when you wanna shut the fan off.

Well, while shopping at an Ace Hardware in Telluride for some bolts, Bob snags something off the shelf in the electrical isle and mumbles "Hmmm this just might work." Here's what he came up with:

Locate the fan relay and remove it:



Purchase 2-pole 15 amp switch, cut off snap tabs and bend blades like so:



Insert into slot for the fan relay - presto! easy on/off fan switch to get me through the rest of the week 'wheeling!



Sorry it's blurry, but you can see it fits perfectly and you can tuck the relay into an unused slot below and to the left so it doesn't get lost/damaged.

I thought this was just brilliant! Made it much easier than having to pull a hot wire from the terminals. This will cause a code and check engine light, but it goes away after replacing the relay and disconnecting the battery for 30 seconds.

Keep the switch in your glove box for those overheating emergencies! :thumbup:

I'm not sure that I would trust a switch that is only rated for 15A max to not melt trying to handle a 40A load. If the wire you was using to jumper the relay termanls was getting hot then it wasn't heavy enough. I've done that on a few occasions to mine and on others using a piece of 14AWG wire, and never had it get hot to the touch.

A/C on would only keep the fan on while the compressor cycled.
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There SHOULD be a high temp sensor that will kick the aux fan in when the coolant temp reaches a point. Fix it or let this senor do it's job. No code, no switch melt down, no early aux fan burn out. No unnecessary load on the charging system. longer battery life (maybe) etc etc.
Keep the switch handy in case the sensor/relay go south on you.

just pull the a/c relay and then turn your a/c on and it will run the fan but the compressor wont run

badron said:

A/C on would only keep the fan on while the compressor cycled.
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There SHOULD be a high temp sensor that will kick the aux fan in when the coolant temp reaches a point. Fix it or let this senor do it's job. No code, no switch melt down, no early aux fan burn out. No unnecessary load on the charging system. longer battery life (maybe) etc etc.
Keep the switch handy in case the sensor/relay go south on you.

Click to expand...

I woulda thought so to.... but I replaced both the sensor in the t-stat neck and the one at the back of the cyl head before the trip. Is there another one I'm missing? There isn't one in the radiator. Anyone know what temp it's supposed to kick on?

96GreenXJjeep said:

just pull the a/c relay and then turn your a/c on and it will run the fan but the compressor wont run

Click to expand...

I'm gonna try that - might be a better way to go.....

YELLAHEEP said:

Anyone know what temp it's supposed to kick on?

Click to expand...

On at 218* and off at 209*.

218 and 209 huh? Well then something isn't working. With new sensors in place, what else could be wrong? It turns on with the A/C, cycles with the compressor, but won't come on when it's hot......

Looks like fuse 18, a 15 amper, provides power to one side of the fan relay primary coil with the key on. The other side of the primary coil is run by a pcm switched ground. You've already verified the output wires of the relay socket both work with BLoose's gizmo.
There's some other circuitry to be looked at if the fuse is OK but my online diagram source isn't getting it done there.
edit: disregard, looks like the same relay is used for both a/c and temp activated purposes so it must be in the wiring between the switch and pcm or a bad switch itself, though it's new- you could always jumper the two pins together and see what happens. I don't know if the temp switch is controlling power or ground to the pcm since that part of the diagram is awol. Guess I'm not much help

i think thats good for when you're in a situation and need it to get home, but i wouldnt run it every day

IslanderOffRoad said:

i think thats good for when you're in a situation and need it to get home, but i wouldnt run it every day

Click to expand...

Exactly - it was put to use to get me thru the event until I can replace the radiator.

I have to admit a mistake--on a 1996, it's 217* (not 218*) and 208* (not 209*). From 1998-on is when the previous numbers would be correct.
Edited for clarification.

Just for information on the rating of a switch. Did you notice the difference in rating vs voltage. The rating is a combination rating that takes into account the amount of metal transferred from the contacts at make and break due to arcing. The rating insures a significant lifetime of switching on and off. If the switch is ON and is not being switched ON and OFF, the DC resistance of the switch actually becomes the rating issue. The switch in question would probably handle 40 amps forever with no issue. The limiting factor is how much heat is generated at the contacts due to the resistance.

96GreenXJjeep said:

just pull the a/c relay and then turn your a/c on and it will run the fan but the compressor wont run

Click to expand...

Ive "got" A/C but the fan doesnt turn off when i put it in the A/C or fan position. Is there something that needs to be plugged in to the AC compressor that im missing?

Is the compresor on the 96 hard wired? I had the same stuation a month or so ago and just unpluged the compresor and ran the AC. Fan on, compresor off.

BBeach said:

Ive "got" A/C but the fan doesnt turn off when i put it in the A/C or fan position. Is there something that needs to be plugged in to the AC compressor that im missing?

Click to expand...

I've got the exact same problem, and the engine overheats when I idle for longer than like 5 minutes. The fan does not click on when the temperature gets past like 220 or even 230. What should be the first thing I check?

I tried unplugging the AC condensor and it still didnt work. Any ideas?

The fan doesn't turn on, or doesn't turn off?

Robert

sorry, double post...

you can run wires into the connectors you have the switch in and run the wires into the cab (with an inline fuse) to a toggle---then you can turn the fan on/off as needed.