View Full Version : New to the SC, Need info on low speed fan circuit.

10-09-2016, 02:28 AM
I recently purchased a 1991 SC with blown head gaskets... After I repaired that, I realized the low speed fan is not running. I have verified the fan works in both speeds by running direct power and I'm not sure if my code scanner is commanding both speeds to run since I only here one click when the fan starts... So now, I need some info or tips on where to go from here.

sam jones
10-09-2016, 04:30 AM
Good morning and welcome

The attachment below will help in troubleshooting the IRCM. It can be repaired (relays) or purchased from this forum or parts outlets (i.e. Rock Auto).


Good Luck.

10-09-2016, 11:17 AM
I like the self-test feature, but I've found it makes it hard to detect sequential clicks. Keep in mind that the fan should normally be started in low speed (high pulls too many amps otherwise) and when the high speed is turned on the low speed should be turned off at the same time. Point is I'd not condemn the low speed circuit just on that point alone.

Last time I had a problem with just the low speed it turned out to be at the connector as the ears had been broken off in the past and the connector wasn't seating together reliably.

Other tests (perform separately)
- engine running, turn on A/C...the fan should run on low

- engine off, unplug the harness at the ECT (pass. side in front of the oil filler cap), then with engine running, the fan should run

- If you want to check the IRCM low and high relays in the car, and if I remember correctly... you can stab a pin in the #14 wire (see diagram linked above; tan/orange), then connect to ground for low fan circuit (circuit hot), and then put 12v into the wire #17 (pink, circuit hot) for high. If you do this, be sure the IRCM is mounted so it can ground.

10-09-2016, 12:40 PM
Thanks for the info guys....

Let me ad, when I self test with the scan tool, the fan comes on in high speed I believe and ramps up to high speed with no pause in between. When I do the same test on my 95 mustang, there is a clear pause of 2 seconds between low and high speed fan operations.

The AC has low charge and won't turn on, I suppose I can jump at the pressure switch and see if the high speed fan comes on, correct?

When I pull the coolant sensor plug, the fan comes on... Is this high speed or low?

I'm sure I can repair the control module if it's at fault, but I'm also concerned the ECU might not be sending the command so I would like to verify that.

Any tips, shortcuts, or personal experiences would be greatly appreciated.

10-09-2016, 12:55 PM
Is the fan on your mustang the same motor/torque/blade design/weight, etc.?

If you hot wire just the high speed circuit at the fan connector, you'll see just that circuit spin up - is that the same response as when you self-test?

No idea how to force test when no freon in circuit...I'd skip it.

When you pull the ECT, I believe that is low speed. The system is not designed to power high just on it's own, without low already having pre-spun the fan, but ECT sensor fail does run fan on an emergency basis, so...

As for repairing our IRCMs, the boards are printed circuit and the relays are electronic. If something has failed, I'd suspect a capacitor. If you're comfortable working board-level and sourcing those components, you should have no trouble. Details via search. Easier to just swap out, I think.

My opinion, tho, is that the IRCM is frequently/incorrectly faulted, when the issue is actually the fan connector/motor, ECT, ECT connector, air trapped at the ECT sensor, etc. I had a pin plunge in a new ECT sensor and not make connection when connected - spent way too much time looking at the ICRM before I found that ;) It's always been a connection/harness issue for me - now I have 4 spares that were originally faulted, but test ok now that I have a better process.

Good luck.

10-09-2016, 01:04 PM
I understand both circuits of the fan should not be energized simultaneously so what I did was make a few pig tails to allow me to energize the low speed fan, deenergize it, then energize the high speed fan. I compared the operation of the SC fan to operation of the fan on both my mustangs, 95/2000 and all seemed to operate the same.

I also swapped the ECT sensor with a good know working unit with the same result. The ECT from the SC worked fine in my mustang triggering fan operation at the correct temp.

10-09-2016, 01:11 PM
I also swapped the ECT sensor with a good know working unit with the same result. The ECT from the SC fine in my mustang, triggered fan operation at the correct temp.

What process did you use to avoid trapped air at the ECT when testing?

Sounds like you've eliminated it from the issue, however.

What is the general condition of the wiring on the front/top of the SC motor?

As part of the HG repairs, did any of the accessory brackets/heads get painted? Is the ground from the pass. side motor mount to the body new?

Did you ground pin 14 on the IRCM?

energize the low speed fan, deenergize it, then energize the high speed fan

It's my understanding that on the SC, the system turns one relay on, and one off at the same time, so two clicks, can sound like one when self-testing...at least that's how it works in my case. Individual testing at the wires 14 & 17 helps to isolate/verify. The only (IRCM related) actionable conclusion when self-testing is if the fan doesn't spin at all.

10-09-2016, 01:20 PM
Heads were media blasted and painted when rebuilt, all other finishes are original.

Wiring poly loom is dry but intact, wiring is good and seems to have continuity throughout.

I'm not fimiliar with the ground strap, can u please expand on that topic.

As for bleeding trapped air, I tried several procedures including cold to warm startup operation with the car lifted at front on stands, bleed as per described in the repair manual, and manual bleeding at the sensor.
If u have any tips on bleeding, I'm all ears!

As for grounding pin 14, no. I'm new to this car but I'm a ford guy by heart. I'm super good with 1979/2004 mustangs and am fimiliar with CCRM issues.

10-09-2016, 01:31 PM
Let me stress that the SC relies on grounds more than any other vehicle I've worked on. Couple this w/Ford's penchant for using grounds to make/break circuits and it's easy to have hard to find issues on the SC. Welcome to the joys of troubleshooting an SC.

The factory installs a ground strap from the pass. side motor mount over to the body, just below the air box, inboard. That strap and body connection can corrode and hide ills - best to replace, not clean, as they are decades old now. As well, the accy. brackets carry required ground paths, and bolt to the heads, so any paint on either may hamper proper (vs. casual) grounds.

Your issue, of course, is trying to decide if outright fan system failure caused the HG issue (not likely if at least the high speed circuit worked at that time?), or arose post-repair. Any idea, or did this car just fall into your lap as-is?

10-09-2016, 01:48 PM
I'm aware of the headaches a faulty ground can cause, they are the major fault I'm most electrical repairs I perform at work. I will remove and inspect the ground straps in a few minutes and if need be, make some high quality straps to replace them tomorrow at work.

This car literally fell in my lap, it's a one owner 85k mile automatic car that was towed to my house as is for a $450 price tag... I heard the engine run for about 1 minute before it was delivered, and know nothing else about its running issues. It was a gamble that could pay off if I repair it correctly and make it a decent driving reliable car.

10-09-2016, 01:51 PM
Have fun & update if you fix any issues.


10-11-2016, 10:09 PM
Just to update...

I checked the engine to chassis ground, the strap was useable but the bolt holding it to the inner engine bay was completely covered in corrosion and I'm sure it was a faulty contact. I cleaned the strap, recrimped the ends and reinstalled it with another ground lead I fabbed on top of it. I also drilled through the hole and installed a larger bolt with better clamping force.

I also inspect the IRCM mounting bracket/connector and found that someone has previously drilled the rivets and opened it since I could clearly see the drill marks on the cover, the rivers were cheap aluminum and not installed straight and flush.

I plan to test the car again tomorrow from cold to operating temp and see if there is any change in behavior... I was not able to start the car since the flu got the best of me on Sunday and layed me out!

Any more leads and tips would be greatly appreciated.

XR7 Dave
10-11-2016, 10:46 PM
Why are you so sure that the fan isn't working? If you hear it ramp both speeds during self test, then it's working and the EEC is able to command it on when it wants to. Yes, the SC test procedure is different than a Mustang, don't compare the two. It can be hard to identify both fan speeds exactly during the self test but if it starts and then ramps up, it's probably working fine. All the things you have stated indicate no malfunction.

You do realize that the low speed fan isn't engaged until 220 deg, right? It may well be that you just aren't getting it warm enough. About the only thing remaining to prevent the fan from coming on is if a low temp condition actually exists at the sensor and that most commonly points to an air pocket. The best way to verify that air pockets have been fully purged is to vent the radiator cap via a lever release and listen/watch for bubbles in the overflow tank. After the system has been open, it's not uncommon to require 4-5 heat cycles and vent releases to purge air. Once you get it to where you can open the lever and releasing pressure results only in fluid but no air coming into the overflow tank, then you are good.

10-11-2016, 11:10 PM
I cleaned the strap, recrimped the ends

And left the corroded wires, inside the sheath, in play....ouch. I'll let someone else explain how electricity travels over the wire's surface, not like water inside a pipe.

If you touch/suspect a ground wire on your SC, replace it - don't try to clean/doctor/repair or otherwise reuse it. Otherwise you're just wasting your time.

Please take this advice seriously - the SC lives and dies on it's grounds. Take chances, cut corners, assume half-measures are ok, all at your own risk. Don't let experiences with any other car color how you work on this one - you'll live to regret it, I promise.

As for the flu.... Captain Jack is your friend ;)


10-12-2016, 09:19 PM
I only left the ground strap installed in order to move the car since it was in parked in my driveway, I made a better quality strap at work this morning and will be installing it tomorrow after I get the car back in the garage. My problem with the low speed fan is not that it's not working but that it's not coming on at the correct temperature which I verified with a external gauge I use for diagnosing... It's definitely coming on late, consistently but late. I keep reading threads online about the ECU malfunctioning and not signaling low speed fan controls at a conservative temp level but have only dealt with this issue on GM cars so this is new on FORD for me. I deal with blowers the size of a small fridge daily and know that heat is not a good characteristic, I have seen damage caused by heat that leads me to air on the side of caution instead of assuming a cooling system is up to par without verifying.

10-12-2016, 09:22 PM
Also, thanks for the tips on burping the system, il give them a try tomorrow then post how it goes...