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Cooling fans

8K views 20 replies 5 participants last post by  sherlock9c1 
#1 ·
hello everyone, so I have a 95 9c1 and both of my cooling fans run at the same time, both fans come on a couple of seconds after start up, so pulled the relays and both are good but when I went to pull fuse I noticed PRI/FAN fuse port is a little melted, how would I go about fixing this problem I have, oh yeah it still works with it being melted, when I pulled the fuse out the PRI Fan turned off right away when I put it back in the fan turned right back on, so I really can’t figure out why both fans run all the time, I have replaced WP, sensor in WP, sensor on passenger side block, thermostat, I haven’t touched the radiator yet, can a bad radiator make both fans run
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#2 ·
The PCM controls the fans so maybe you should start with getting live data out of it. You may have a broken sensor wire. You gave no information on what the dash gauge shows. Is it reading normally?

Do a search of the forum to decide how you want to get data out of the PCM. Laptop and cable or scanner are choices. A diagnostic charge from a mechanic might have been cheaper than the parts you threw at the car. Just be sure they have a OBD1 scanner.
 
#3 ·
It looks like your fuse box has seen better days. Get a fuse box and swap it in. Again this has been talked about before. This current thread has a lot of info, diagrams, ect.

 
#5 · (Edited)
Normally when we want to check that the fans and the PCM work we unplug the temperature sensor and the PCM defaults to fans on for safety. A broken wire would also force the fans to run, So you could unplug the temperature sender and the PCM and test the wire between them.

Again does the temperature gauge work?

The fuse box seems to work from your description but it may fail in the future.

I live in California, LA everyone has an LS motor no one has a LT1 anymore
My understanding is you have to do a emissions test. It is hard to believe only test stations have OBD1 and no one has a OBD1 for repair or pretests.

If you have a laptop, a cable and software cost about the same as a couple of hours of mechanic's fees. I agree it is hard to shop for a scanner but the California population is close to the size of my country's population. I bet someone is selling one now or pretty soon close to you. I had to shop for six months.
 
#6 ·
Your fan relays should not be inside the fusebox (anymore). There is a Tech Service Bulletin that relocates the fan relays OUTside the fusebox by the wiper motor, specifically because they tend to melt in the fusebox.
Gary @ Innovative Wiring makes a fan motor & relay harness specifically to avoid this ever happening again; it improves on GM's Tech Service Bulletin and is worth every penny.

You already replaced the H2Opump temp sensor, but the wiring that leads away from the H2Opump temp sensor back to the pcm may also be compromised even if the sensor itself works.

If something's wrong with the AC pressure sensor, it might also be commanding both fans to stay on, but this is even more unlikely.

Ultimately, you need some kind of OBD1 datalogging to see if either the H2Opump temp circuit is compromised, the AC pressure sensor is misreporting, or some other sensor issue is tricking the fans into staying on constantly. Sorry.
 
#7 ·
....... the wiring that leads away from the H2Opump temp sensor back to the pcm may also be compromised even if the sensor itself works..........
The wiring and connectors get more than their share of discussion about problems with that sensor.
 
#14 ·
That may be GM's TSB for your 2ndary fan, which unfortunately was only implemented on 9C1 models AFTER melting inside the fusebox.

(25 years later, some people continue to insist that they do not need to perform this or that TSB because their car never had the symptom that would warrant it, whereas I needed considerable convincing in my early 20s to NOT have a preemptive appendectomy. I still wonder if I should remove my appendix, but am sure every Ironblock LT1 should disable its AIRpump.)
ANYWAY

Please forgive the following.
Disconnecting the H2Opump's coolant temp sensor makes the pcm say, "the difference between the IAT sensor and the H2Opump sensor is frakken bu11$h!t; run both fans just in case".
However there are several other things that can happen that can make the pcm run both fans just in case, but for the life of me, I cannot remember any of the other conditions that make the pcm do this, and it's been long enough that I cannot remember which forum elder would know.

Nonetheless you should find out WHICH of these specific conditions is causing your pcm to do this.
Ultimately this is why I and others resort to suggesting that you get an OBD1 scanner of some sort.

If you really wanna get your money's worth, get yourself
an OBD1 cable (I'll only endorse TunerCAT's $85 cable, you can find one for less, I hope it's as trouble free)
$EEhack (free, yet still being improved, can do lots more than just help you find out why your pcm is running both fans)
 
#18 ·
That is one helluva better rez of the TSB than the little image I found. Good you confirmed GM's official TSB applied to only one fan, and also in confirming it applied to only 9C1 and SEO. Also appreciate correcting that it (the TSB at least) applied to the primary v. secondary as previously got misstated. I'm not catching much other errant info or misdirected guidance that's been offered.

This TSB never made it to recall status even for the cop cars, and made it 25 years without me hearing about it once. The OP is making out like a bandit with all the background and direction here, and he sounds on it well enough just to closely inspect his own fusebox for signs whether to apply some or all (or with regard to Gary's kits even more than) the TSB to his own problem(s).
 
#19 ·
193504


Lets get back to the OP’s issues.

I suggested replacing the fuse box. Why fuse #7’s space is melted. The OP has made NO mention of melted relay sockets, AND reports that the relays control the fans. It might be in the OP’s interests to provide diagnostic suggestions and leave upgrades until the original problem is solved.

The melted #7 fuse area is connected to the primary fan relay coil. So replace the relay and relocate it like the TSB.

NO. The relay coil draws less than 0.5Amp and a short should have blown the fuse.

Well there is the problem the “crazy GM engineers” used a 10Amp fuse.

No. This fuse is also the power fuse for the A/C clutch coil. The melting may be the result of issues with the A/C clutch system slowly overloading the circuit or persons unknown using a larger fuse while messing with the A/C circuit.

There has been a lot of messing around in this box. Three different relays and the OP is asking about a extra relay outside the box.

Bad temperature information, malfunctioning A/C are issues that should be checked out. They are things that “fool” the PCM to run the fans.

The problem may be complex and the OP could help the forum help him by getting a FSM. Then we could refer to and discuss things without scanning, typing, and posting things that may still be covered by copyright laws.
 
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