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Swapped a new sensor into my secondary fan rad sensor and fusible links started smoking


The_Ginger_Stig
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I've been having a ton of cooling problems in the Arizona heat, gauge gets close to 3/4 and I have to panic park and wait . So I figured replacing the secondary fan sensor that was broken (it spun inside the housing) would maybe help alleviate some heat. I ordered a 180 degree thermo-sensor because the goal was to get both of the fans to come on to try and cool it down a little. While I was checking the secondary fan by simply grounding out the connector I noticed something weird. The AC fan turns on (fan in front of the ac core) but the secondary fan itself does not. I thought it was weird but I decided to test it all anyway just to see. After getting the car up to temperature and having the primary fan kick on, the secondary never did work which is weird because the switch should be the same temperature. However, my fusible links started smoking and I immediately cut the ignition and waited a bit. I tried again without the AC fan plugged in and no smoke, but the secondary fan never did kick in after letting it warmup again and having the primary kick in. Is there any place that the AC fan relay and the secondary fan relay are connected? And why would the AC fan draw enough amperage by itself to start overheating the links? My links are old, but I've never had them overheat or smoke before. Any tips and help is appreciated thank you :)

notes on my current cooling situation:

  • cxracing starion radiator (fan grounds are securely bolted into the rad)
  • stock 3 electric fans
  • undertray is currently off and has been because it's easier to work under there
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I have gone over almost all of the grounds in the engine bay and cleaned them a while back but I can try cleaning them again. Do you or anyone else know why the AC fan might kick on when the secondary fan has power? I remember reading something a while back that said something along the lines of them having a fail safe in case the engine  was way too hot but I can't find the post nor the wiring diagram for the fans in the FSM

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update, tested the secondary fan as per the FSM suggests and it's dead. Makes me grateful that it didn't work if only the AC fan almost burned down the car. For anyone else searching for similar answers on why the secondary and AC fan kick on together, their relays are wired together so if one kicks on the other will too.

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Dang that's a good place to start looking thank you. If I measure the resistance between the two terminals would I be looking for super low resistance from a potential short? Since oem replacement motors are around $250 right now would I have a chance at rebuilding it?

Edited by The_Ginger_Stig
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Good to know. My car never overheated when it was in Washington state but as soon as the Arizona weather hit it's been a constant struggle. Even with that giant aluminum radiator CXRacing makes it still gets hot sitting in traffic. The car only has around 45k miles so I hope it's not losing its head or head gasket, but I've started to doubt anything on these old cars will last another 3 years haha.

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Secondary fan and the AC fan are wired in parallel. Take a look at page 90 HERE

I would grab a meter and check resistance through that secondary fan. If it was a dead short or close to it. That would cause the issue. You can pull the secondary fan relay out and let it warm up again. Should see the AC fan come on close to when the primary comes on. 

Edit: posted before I saw your response. Sounds like you found the issue though!

Edited by psu_Crash
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@psu_CrashStill haven't found the issue :(, just responding to TexasQuest. I'll check the secondary fan as soon as I can. If I'm reading the wiring diagram on page 90 right, it looks like pulling out the secondary fan relay would bypass any power going to the secondary rad fan until the pressure switch, dual pressure switch, or the engine coolant temperature switch closes right? So if I pull the secondary rad fan relay out and the AC fan comes on immediately when the ign swt is turned on it suggests that 1 or more of the 3 previously mentioned sensors might be faulty?    However, if I pull out the secondary rad fan relay out and the AC fan doesn't immediately turn on and instead it turns on around the time that the Primary fan turns on, it suggests that there might be a fault in the secondary rad fan relay correct?

I'll be checking the resistance of the fan and will update within the hour.

 

I'm terribly sorry if that was too many questions or worded too poorly, I'm battling against time in college right now and I didn't get much time to read through the diagram.

I'll drag this car kicking and screaming to a daily driver status but it might take awhile :)

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17 hours ago, The_Ginger_Stig said:

@psu_CrashStill haven't found the issue :(, just responding to TexasQuest. I'll check the secondary fan as soon as I can. If I'm reading the wiring diagram on page 90 right, it looks like pulling out the secondary fan relay would bypass any power going to the secondary rad fan until the pressure switch, dual pressure switch, or the engine coolant temperature switch closes right? So if I pull the secondary rad fan relay out and the AC fan comes on immediately when the ign swt is turned on it suggests that 1 or more of the 3 previously mentioned sensors might be faulty?    However, if I pull out the secondary rad fan relay out and the AC fan doesn't immediately turn on and instead it turns on around the time that the Primary fan turns on, it suggests that there might be a fault in the secondary rad fan relay correct?

I'll be checking the resistance of the fan and will update within the hour.

 

I'm terribly sorry if that was too many questions or worded too poorly, I'm battling against time in college right now and I didn't get much time to read through the diagram.

I'll drag this car kicking and screaming to a daily driver status but it might take awhile :)

Not too many questions at all. We will get you there :)

If you pull out the relay that will take the fan out of the equation, but the AC fan will still run. 

With the relay out your AC fan should come on normally with either thermosensor 2, dual pressure or the pressure switch. Engine coolant switch isn't tied to the AC fan. You could jump ground to each of those, or any of those for testing purposes without having to let the car run. 

If that all works as it should with the relay pulled, then yes, you have an issue with either the fan 2 relay or the fan itself. I would put my bets on the fan motor or potentially wiring going to it. 

Edited by psu_Crash
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Oh boy. So I pulled out the 2nd rad fan relay (the relay on the right from the group of two relays with rubber shielding behind the horn)  as indicated by the FSM here, and none of my fans ever turned on. I got a used but good fusible links box for the head, tails, eci, etc and have all new links in it. The links didn't smoke or even get too hot so that solves the original problem I guess, but now I don't know why the primary fan and AC fan won't turn on. I did discover a massive new exhaust leak though :(. Did I end up pulling out the wrong relay?

I currently have the AC fan plugged in but I had the 2nd rad fan unplugged to avoid running power through it because if it's shorted then it'll probably just burn up the new links right? Looking at the wiring diagram on pg 90 of the FSM it looks like the only way that the "Radiator fan air condition relay (1)" can get power is through the 2nd fan motors connector but some of the other relays should have closed right? To restate: Primary fan and AC fan never came on even after the car was fully warmed up and a bit past half way on the coolant temp on the dash. My primary has never failed to come on at exactly halfway on that gauge so I'm completely stumped.

 

edit: I retried getting the fans to work at all with the secondary fan plugged in this time and without the secondary fan relay and still no dice. Fuse links didn't get too hot with the secondary fan plugged in though.

 

Side note for anyone that needs some NLA fusible links, I actually found some wire on the jungle site.

The oem Mitsubishi quick connect terminals are a little bigger than standard sizes so I just ordered a

pack of standard size terminals and opened them up and adjusted them.

This wire can be used for "green"  fusible links, .5mm^2

This wire can be used for "red" fusible links, .85 mm^2

Edited by The_Ginger_Stig
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The problem has been found! When I bought a new primary thermosensor to replace the secondary, I made the mistake of trusting a cheap ebay listing that had the right part number. The reason the secondary and ac fan are always on is the sensor is always grounded. As I understand from the FSM, the sensors should only ground when they're at a specific temperature. My next adventure is finding a real primary sensor and probably a replacement secondary fan because mine sounds pretty unhealthy but I'm pretty sure the issues have been found and can be resolved. As for the reason my links were smoking... oh man I feel pretty bad for this one but I had the primary link going off the battery probably 2.5 X the length of the original one 😕 After it's been replaced with a fresh one and cut to the appropriate length it still gets hot-ish but normal link hot-ish. If anyone has a known good primary sensor or a good secondary fan I'll take both. Thank you to everyone that helped me 👍

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31 minutes ago, The_Ginger_Stig said:

The reason the secondary and ac fan are always on is the sensor is always grounded

That will do it every time 😉

Just go to summit, jegs or the like and find a thermoswitch that has the correct threads. I picked one up at the local NAPA... 10+ years ago. Might get lucky though!

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Thanks Texas, I just ordered this thermosensor because it looks like it has the on off temp inscribed on the outside and has MB007639 in its description so maybe it'll actually work. I also ordered the one from CoolCat to keep as a spare or use if the other one doesn't work. Drove a decent bit today and the car seemed to be doing really good on temps (under the halfway mark), but it was still only around 75 this morning so we'll see how it holds up after the heat hits. The bearings in the secondary fan seem to be crying for help so I'll probably end up using a "slim" ebay fan that uses the same amperage or less eventually.

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