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Discussion Starter · #1 ·
So I hopped in the car for a trip to the grocery store today, and noticed my AC wasn’t cooling at all when at a stop light. It cooled fine, the second I started rolling again. I clicked on my gauges menu to see what the head temp was, and saw that it would climb rapidly when stopped. I knew right away that the cooling fan wasn’t working.

The car never over heated, but head temp did go to 220°F for a quick second. I altered my route quickly, to avoid stops, and managed to keep temps around 210°F so I’m not worried about the engine. It’s fine. I got the car back home without any overheating issues, but now coms the task of diagnoses.

After checking / swapping all relays, I’m thinking the fan resistor module, or the plug connector has failed. The car has a new (1 year old) SVT 7-blade GT500 fan, as I need the extra CFM to draw more air through my heat exchanger (the fan also drastically improved AC efficiency).

Having never actually had to replace the resistor module before, I wonder if it’s common, or even possible, for it to fail in such a way, so as to lose both high & low side functionality, or is more likely to be the connector / pigtail has melted?

I have a spare fan/resistor module since I kept all of my original parts. I’m hoping I can just use the old resistor module and call it quits. If the whole fan has failed (which I’m praying it didn’t), then I’ll have to put the original 6-blade fan back in, and order another 7-blade model (ridiculously priced).

So, my question goes out to 5LHO regarding removal. Do you think I can simply lay-aside both cooling reservoirs without disconnecting the lines? I’ll be working in 95°F - 100°F weather, with no shade, and in a dirt yard with no grass. It’s going to be miserable. If I can eliminate disconnecting the lines, things will be much less nasty.

UPDATE:
I decided to dig-in and inspect this morning. I was able to move the passenger side reservoir tank just enough to access the fan connector and remove the resistor module. The resistor unit was fine, but the wiring-harness connector was burned and mutilated.

I scraped off the melted plastic, then did a little scraping of the resistor spade connectors. I tried to clean the connectors on the wiring harness, but that proved impossible. However, those connectors looked pretty good anyway.

After cleanup of the aforementioned connections, I put it all back together and tested. Both high-speed & low-speed are now working.

I know this makeshift repair will collapse on me soon enough, but at least I can order the harness pigtail and drive the car until it arrives (hopefully). Then I’ll make a proper repair. I’m considering modifying the connection to prevent a future occurrence of this.
Automotive lighting Bumper Telephone Automotive exterior Telephony


This one isn’t mine, but mine looks EXACTLY like this.
 

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Fans are controlled for speed by resistance so, I'm not surprised it stopped due to that. I recall an occasional issue like you describe with early cars regarding the fan module wiring. It's possible the high demand fan put more pressure on the wiring.
 
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Discussion Starter · #3 ·
Fans are controlled for speed by resistance so, I'm not surprised it stopped due to that. I recall an occasional issue like you describe with early cars regarding the fan module wiring. It's possible the high demand fan put more pressure on the wiring.
I pulled my original fan from before supercharging, the resistor was burned out, and the spade connectors had plastic-slag on them too, so I don’t think it’s the new fan. I think the pigtail should have been replaced when the new radiator and fan were installed, but it got overlooked. I wish I knew how to prevent this from reoccurring.
 

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IIRC, the pigtail being marginal existed with the original fan. I just suggest adding load would not have made the situation better. It's a penny-pinch, 1/2-assed design, sorta like the old Ford 2G alternator plugs on the fox body cars. I wonder what the GT500 connector looks like and/or if it has a better version of the same system?
 
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Discussion Starter · #5 ·
IIRC, the pigtail being marginal existed with the original fan. I just suggest adding load would not have made the situation better. It's a penny-pinch, 1/2-assed design, sorta like the old Ford 2G alternator plugs on the fox body cars. I wonder what the GT500 connector looks like and/or if it has a better version of the same system?
Yeah, I’ve thought about that too. The GT500 uses the exact same connector. The problem persists all the way through 2017 mustangs as well. I’m considering making an improvised upgrade after the connector is replaced. Perhaps a second set of connections by way of additional wires the jumper over/around the connector to reduce the load on the spade terminals.

It may not be the best solution, but I’m kicking it around.
 

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I had to have my 99 Mustang six rebuilt because my cooling fan died - blew a radiator hose, tried to limp home with a hose bandage. Gauge never reached red, kept adding water, with radiator cap loose - but engine started getting oil in coolant intermittently after this, usually around town. One thing I would really like to see is an indicator light that would show you the fan has failed - or is not getting power.
 

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Discussion Starter · #7 ·
I had to have my 99 Mustang six rebuilt because my cooling fan died - blew a radiator hose, tried to limp home with a hose bandage. Gauge never reached red, kept adding water, with radiator cap loose - but engine started getting oil in coolant intermittently after this, usually around town. One thing I would really like to see is an indicator light that would show you the fan has failed - or is not getting power.
I watch my CHT at all times. The dummy gauges are junk. I put a Bandaid on it (cleaned up the connector) and it’s working for now. It’s hot here, and my immediate tell, was the AC not blowing cold. As soon as that happened, I knew what the issue was, and I monitored my CHT closely. It didn’t get anywhere near being overheated, but I knew it would, so I shut it down, figured a new route where I could keep the CFM up, and got home without incident.

My harnesses (body-pigtail) came in from Ford. Unfortunately I got smacked down hard with COVID-19, and can’t even get out of bed at all. The repair will have to wait until I’m well, or dead.
 

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Well, take care of yourself and get well soon!
 
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Discussion Starter · #9 ·
Thanks, VA doc sent some Paxlovid. I’m hoping this will shorten recovery time. The stuff leaves a crap-nasty taste in your mouth 24/7. So far I’m at middle of the road severity.
 

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Discussion Starter · #10 ·
So I finally recovered and did a proper replacement (and some long awaited mods). Car is running stronger than ever. I installed Roush High-Flow Upper & Lower grills. Man it made a huge difference. I realize that some users who installed these updates, got very little benefit. I got such great results, I hesitate to mention, for fear of being called lier.

I suspect my improvement was because my airflow was very restricted. I run a thick racing radiator, and a thick heat-exchanger. These items probably couldn’t reach maximum efficiency with the lesser air-flow of the stock grills. Combine the increased airflow through the new grills, and the heat-extractor in the GT500 hood, and it really moves a lot more air than stock. I can actually feel the difference on WOT pulls, and my CHT’s are drastically lowered across the board.

Next year, I’m considering an even bigger heat exchanger (DOB Titanic), larger cooling lines, beefier HE water pump, and either a modified intake manifold/intercooler with 1.25” coolant lines, or the one made by DOB with those mods already built-in.

I’m just a little hesitant on this because, I’m unsure how the DOB designed intake manifold compares (performance wise) to the Roush intake manifold. I’ll need to do some research on that aspect. Also, I’m so happy with the way my car runs now, I kinda don’t want to tamper with near perfection. It already runs much better than it ever did new, and it has taken some work & tweaking to get it there.

I’m not sure I want to “upset the apple cart”.

Here’s a pic with my new grill-set, and the relocated Foglights.
Car Vehicle Plant Grille Automotive lighting
 

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Serious, definitely. Gotta know when you're happy and stop there, man. What fogs are those? They don't look like the CS jobs I installed on my own car.
 

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Discussion Starter · #12 ·
Serious, definitely. Gotta know when you're happy and stop there, man. What fogs are those? They don't look like the CS jobs I installed on my own car.
They‘re Roush, with the Diode-Dynamics SL1 kit installed. Kind of spendy, but the results are fantastic.
 
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