zfinger Posted July 7, 2014 Share Posted July 7, 2014 I need some wiring help. 1990 4.0L Previous owner had some sketchy wiring I removed and I'm re-doing. The leads into the AC fan have been cut. I remember doing a mod on my 97 XJ that let me turn on the AC fan like an auxiliary fan. I think they had something similar going on. On the drivers side under the air box is a harness with cut red and black wires going nowhere. No current to the red wire with key on. Also theres either a temp sensor or a temp switch in the radiator hose. Is that stock or was that added? Switch or sensor? On the passenger side there are red and black wires coming out of the harness that someone added clips to. Red tests hot and black is a ground with key on. It's my understanding that the AC fan runs when the AC is on, or when the coolant temp reaches a certain point. True or false? If the fan comes on when the coolant temp hits a certain point then why add a switch to the system? Or is the mod to make it so it comes on with coolant temp where it didn't work like that before? Link to comment Share on other sites More sharing options...
yxmj Posted July 7, 2014 Share Posted July 7, 2014 The sensor/switch in the rad hose is not stock.....my guess it was to turn on the aux fan......my guess on the other wires would be a manual over-ride switch....are there any aftermarket toggles in the cab? Link to comment Share on other sites More sharing options...
ParadiseMJ Posted July 7, 2014 Share Posted July 7, 2014 The radiator is a 91+ radiator. A 90 does not have a cap. The 90 also has a bung between the tranny lines. That is indeed some sketchy wiring. My thought is that the PO replaced the radiator, in an effort to make it an open system. Then used a regular old sensor to wire it in. Which won't work, because: There are 3 heat "sensing" devices in a Renix Jeep. The one in the radiator is a switch. It's ONLY to send a message to the aux fan relay to turn on/off the fan...nothing more. The one in the block, below the manifold, is a sensor. It sends info to the ECU to adjust the fuel/air mixture when the engine is cold/hot. The one at the rear of the head is a sender. All it does is run the gauge/light on the dash...nothing more. None of the sensors are interchangeble as they all use different systems to activate/indicate information. The HO models (91-95) used the sender in the back of the head AND the one in the t-stat housing and did not have the one in the radiator. So when you (or the PO) put in a later model radiator without a bung for the stock switch you lose the automatic temp switch function altogether. The later models...after 95/96 intwegrated the switch/sensor/sender into one unit on the t-stat housingYou can't buy a switch that'll work since a.) the relay seems to be gone and b.) it's a switch...not a sensor and c.) it's FUBAR. So, all that being said...whaddya do? Personally (actually this IS what I did) I'd go to the junkyard and find a Renix Jeep, pull the relay off the fender with wiring attached and splice it in to what you have there from the fender to the plug for the switch. Then I'd wire in a manual switch to the dash. Why keep the plug? Because fast-forward 4 years later (or in your case maybe sooner) I replaced the radiator with one that DID have a bung for the switch. The plug in the Jeep was still there, so I also pulled a switch out of an 89 which works perfectly now, plus the switch ALSO works on the dash. You really do need the relay too because when the fan starts up it pulls quite a bit of juice, the relay protects the switch and the fan. Good luck Link to comment Share on other sites More sharing options...
Keyav8r Posted July 7, 2014 Share Posted July 7, 2014 My 88 had the fan switch in the hose as yours is shown. The radiator had been replaced before I bought it and had the bung (where the finger is pointing in ParadiseMJ's post). I replaced the hose (actually, all of the hoses) and moved the switch to the bung in the radiator. Fan works as it should when temp rises. Can't comment on operation with the AC as the AC is inop. Link to comment Share on other sites More sharing options...
zfinger Posted July 8, 2014 Author Share Posted July 8, 2014 So if I take the "switch" that should be in the radiator and relocate it to the hose where there appears to be a "sensor", would that work? All that changes is the location. The AC fan is actuated by coolant temp even if the AC is off correct? I just bought this truck, haven't even heard it run yet. I have no idea if the AC works or not, and that'll determine more on how I fix this. There were remnants of a switch on the dash, two relays under the hood (a 4 and a 5 pin), and 4 ugly fog lights I removed. I got a little aggressive removing non-factory wires thinking they all went to the lights. Apparently some went to the fan. Link to comment Share on other sites More sharing options...
Keyav8r Posted July 8, 2014 Share Posted July 8, 2014 No, your switch will have to stay in the hose fitting because your radiator doesn't have the bung fitting on the tank. My radiator had the bung with a plug in it. I bought all new hoses and planned to cut the lower radiator hose to accept the "tee" for the switch until I noticed the bung fitting on the radiator. Putting the switch there gave me a one piece hose from radiator to pump and eliminated two hose clamps and potential leak points. The truck ran fine before I replaced the hoses and moved the switch and AFAIK that arrangement may have been OEM. Link to comment Share on other sites More sharing options...
ParadiseMJ Posted July 8, 2014 Share Posted July 8, 2014 Sorry, I did not see the switch in the hose in the first picture. I was just looking at the funky wiring. If the switch is wired in through the relay, it should work. But with the birds nest of wiring splices and whatnot* there I doubt it. The switch should activate at a temperature adjusted at the gauge of 218-220 and go back off at 215-217 roughly. I say adjusted because the temp coming out of the bottom hose will be actually lower than the indicated temp on the gauge at the back of the head. That switch and the set-up with the hose should not affect the way the Jeep runs as all it does is turn off/on the fan. It has no connection to the ECU.. When you trun on the A/C on the Renix models the fan should run when the compressor runs (cycles). That, and the noise the compressor makes is why it's noisier under the hood. *I've chastised my son before for constantly using the term whatnot, but here it sure seems to apply. Link to comment Share on other sites More sharing options...
danbyrambler Posted July 8, 2014 Share Posted July 8, 2014 Many prefer the fan switch in the T stat housing - Got a pic of your housing? Link to comment Share on other sites More sharing options...
ParadiseMJ Posted July 8, 2014 Share Posted July 8, 2014 You can indeed just use a 91+ t-stat housing to install a sensor BUT finding a switch that will both fit AND work as a switch is problematic. I first just went and got a sensor but the connector was wrong (and even if you spliced the wires...it's a sensor, not a switch) so I explored using a sender and just splicing the wires (same deal) but I was told that neither the sender or the sensor would work because of neither one was actually a switch. In a 91+ (HO) the sensor and switch are integrated but since the wiring goes to the ECU to tell the fan to activate and the Renix ECU has no such function. The 96+ sensor in the t-stat is also integrated for the gauge, ECU and fan. The Renix switch is just wired into the relay, it does not go to the ECU. There was some information that a GM (Corvette specifically) had a similar working switch but the temp it activated the relay at was somewhere around 190 on the gauge...so in actuality about 150 at the switch. I don't have any real data on that. Link to comment Share on other sites More sharing options...
danbyrambler Posted July 8, 2014 Share Posted July 8, 2014 The switch I used on my 87 was an Airtex 1s4346 - 3/8NPT - single wire - closes 218 F plus/minus 8 - opens 213 F - - - Used it to trigger a relay - - worked fine - -IIRC it actually made at 220/222 & opened around 208/210 according to my IR laser gun - Had to shield the t stat housing wi a piece of cardboard to get readings when fan running Link to comment Share on other sites More sharing options...
ParadiseMJ Posted July 8, 2014 Share Posted July 8, 2014 Well, ya learn something new everyday. I looked all over for a switch that would do just that. So if it works...that would be the way to go...so to the PO get yourself a 91+ t-stat. It'll fit in the same space, same gasket, same bolts...it'll just have a bung in it for the switch. ...and to danbyrambler...I'm saving that p/n for future reference. Thanks for the info. Link to comment Share on other sites More sharing options...
HOrnbrod Posted July 8, 2014 Share Posted July 8, 2014 Here's a list of various temp switches categorized by degree ON/OFF, thread type, and electrical connector type. Take your pick for your application. http://www.airtexve.com/custom_searches/ds_fans.php?showall=yes Link to comment Share on other sites More sharing options...
zfinger Posted July 10, 2014 Author Share Posted July 10, 2014 I opened up the wire loom and traced some stuff. The fan control relay is still on the DS fender and appears to have all factory wiring. The yellow & grey/blk wires going to the switch in the lower radiator hose look correct. The red and black wires are cut and go nowhere. I'm assuming they were meant to go to the fan. I should just be able to hook the red and black wires back to the fan and the fan should operate as it did from the factory. I don't see any reason to have an override switch in the cab. Red out of the relay doesn't get power with the key on. Jeep isn't currently running so I can't bring her up to temp and see if the red wire gets power once the switch reaches temp. I've still got a red and a black wire coming out on the harness on the PS. Red is hot with key on and blacks a ground. Any idea where they go? Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now