94 mustang GT electric cooling fan control

ninjafury · Feb 23, 2008

I'm helping a friend with his 94 5.0 which has been overheating. We replaced the thermo, & radiator cap which seemed to help. The problem is now that the 2 speed electric cooling fan never comes on even when the car gets hot. I heard that there's a recall that has something to do with the fan. I jumped the fan to the battery & it works great. My question is, what should we do next? Is it possible that the head temp sensor is bad? I was considering just buying an adjustable thermal switch & placing it in the radiator then wiring it to CCRM so the fan comes on at the right temp. Correct me if I'm wrong, but the green & purple wire (#17) just controls the fans high speed setting. How can I access the low speed setting?

HISSIN50 · Feb 23, 2008

Someone else recently posted a very similar scenario. Was it your friend?

In any case, check the fan fuse in the underhood fusebox. Check the fan connector to ensure it is mating to the terminals in the fan motor (which are known to char). The ECT (which is the temp sensor that the puter uses for the fan) is on the front passenger side of the engine. If the fan wont come on with the AC turned on, or the ECT momentarily disconnected, the ECT is probably not the problem (or the only problem).

For upstream diagnostics, see the EDF/HEDF portion of this tech note.

If you want to fix the issue, you should be able to. If you want to circumvent the issue, you can. You need to be careful though. If you want to have it function like OEM (two speeds), you will probably need several relays in total (up to you if you reuse the CCRM relays). You do not want to have high and low speed running at the same time. And it isnt ideal to go from off to high. You'd have a power relay for low, one for high and then a control relay. The third will shut off low (which is controlled via the controller you purchase) when the AC is on (or whatever you use to trigger high speed).

If your friend has the funds, consider a Dc Control unit. You'll never look back.

Good luck.

ninjafury · Feb 23, 2008

Thanks a lot for the reply! Very helpful. I would like to restore the stock system to operational, then maybe add an additional thermal switch that comes on at a high temp as a backup. My friend uses his car for his job & he drives it pretty hard, so bullet proof would be nice.

I will check the fuse & change the head temp sensor. Is there anything else that can keep the fan from working? Like air bubbles?

HISSIN50 · Feb 24, 2008

ninjafury said:
Thanks a lot for the reply! Very helpful. I would like to restore the stock system to operational, then maybe add an additional thermal switch that comes on at a high temp as a backup. My friend uses his car for his job & he drives it pretty hard, so bullet proof would be nice.

I will check the fuse & change the head temp sensor. Is there anything else that can keep the fan from working? Like air bubbles?

For your thermal switch back-up, that would work fine. Since it hopefully won't ever be needed, you can probably just tie it into the high speed fan relay input (Pin 17. It gets grounded to turn high speed on). Or also use your own relay and tap into the load-side of the high speed fan circuit.

Air bubbles can affect sensor and sender readings, which would in turn affect the fan. If the system hasnt been opened of late however, chances of air being a factor are slim. Most of us have aftermarket gauges so we know what's going on. Even if temporarily installed and removed, or mounted in the engine bay (if the owner doesnt like aftermarket gauges inside his car), this helps a ton. They even have gauges in radiator caps these days. The stock gauge is just kinda tough to interpolate (esp if one doesnt have a cross reference like the ability to read Pids or datalog, etc).

Couple more random things you can try: if you run self-diagnostics, the first thing the car does is cycle each fan speed. This is a quick tell to see if the circuit is intact.

If you disconnect the ECT electrical connector and start the car, the low speed setting should come on.

If you ground CCRM Pin 17, the fan should come on high.
If you apply fused 12 volts to CCRM Pin 14, low speed should come on.
MAX AC should make high come on.

Checking any or all of that can be telling in narrowing things down.

Good luck.

ninjafury · Feb 24, 2008

Thanks again for all the help! It is very useful information. Hopefully we can get this thing sorted out. I'll post back here once it's done.

earleys94gt · Feb 24, 2008

Look here, #12 in Table of Contents.

http://forums.stangnet.com/showthread.php?t=665335

ninjafury · Feb 25, 2008

I replaced the coolant temp sensor, bled the system, & replaced the cap. The fan works but the motor seems worn out. The car still seems to get little hot, the needle gets up around the A in stop & go traffic. The cooling system is very clean, the water pump is fairly new, the thermostat is a 195. Should we try a 180? or do we need to replace the fan motor? Also, the high speed does not come on with the max AC, any idea where to start?

HISSIN50 · Feb 25, 2008

ninjafury said:
I replaced the coolant temp sensor, bled the system, & replaced the cap. The fan works but the motor seems worn out. The car still seems to get little hot, the needle gets up around the A in stop & go traffic. The cooling system is very clean, the water pump is fairly new, the thermostat is a 195. Should we try a 180? or do we need to replace the fan motor? Also, the high speed does not come on with the max AC, any idea where to start?

If you hear bearing noise from the fan, it might be wise to replace the motor or assembly. This could save a meltdown down the road.

Though it's tough to interpolate the stock gauge, I suppose you could try to infer relative differences. For instance, if the car runs much cooler on the highway, that could signify that the fan is not keeping up. However, the stock fan on temps are so high that this can skew results. Once the fan comes on, it should pull the temps right back down (about 8*F for low speed).

High speed not coming on with the AC can be a couple of things, the most common of which is seems to be the high speed driver in the PCM. That was the deduction I made in my case (my fan would just stay on low speed with the AC). I ditched the stock fan control and never looked back (after exhaustively troubleshooting the circuits).

ninjafury · Feb 26, 2008

Thanks again for the VERY helpful information. The reason we think the car is still running hot is because it used to run around the O & the R, now it's closer to the A & L. Sometimes creeping up uncomfortably close to the L. The car doesn't get hot enough to boil over or ping, but it feels sluggish & sounds lean. I think today we're going to install a mr gasket 180, clean the bugs off of the radiator & install a new fan motor. The A/c definatly is not triggering the high speed fan, the low stays on like yours. What type of fan control did you switch to? Is there a way to wire pin 17 to the A/C controls? I think we might try to keep the stock setup until summer. Thanks again!

HISSIN50 · Feb 26, 2008

ninjafury said:
Thanks again for the VERY helpful information. The reason we think the car is still running hot is because it used to run around the O & the R, now it's closer to the A & L. Sometimes creeping up uncomfortably close to the L. The car doesn't get hot enough to boil over or ping, but it feels sluggish & sounds lean. I think today we're going to install a mr gasket 180, clean the bugs off of the radiator & install a new fan motor. The A/c definatly is not triggering the high speed fan, the low stays on like yours. What type of fan control did you switch to? Is there a way to wire pin 17 to the A/C controls? I think we might try to keep the stock setup until summer. Thanks again!

I treated myself to the Dc Control unit. I figure that if I'm going to do it, do it right (especially since I live in the desert). I never looked back.

If you have Low not switching off for AC, you have a couple of rig-together options. You could just re-pin the fan motor so the 'low speed' wire now connects to the fan's high speed terminal. Now at 208*F or with the AC, high will come on. Not a great solution but it should work for a little while.

You can also ditch the OEM relays and use a cheapo controller with two relays to drive high speed or use 3 relays to maintain two speeds.

Just consider the cost of anything you choose to do. It's easy to toss some cash at junk when for a little more money one could have had a really nice controller. That was my rationale. I now have a PWM'd controller that tells me how much my fan is working (relatively speaking) and allows me to adjust my target temp from inside the cockpit.

ninjafury · Feb 26, 2008

I think the dc controller may be our choice for the near future. I'm not too worried about the A/C right now, we just want the car to drive down the road & not get hot. I thought we were doing better until today, the fan quit again, & now the water pump is leaking! The fan motor seems to work intermittently. I pulled the connector & jumped it, & it would not spin, waited maybe 10 minutes, tried again & it worked. I re connected the plug & we took a short drive through downtown to the dealership to price a fan & it seemed to work the whole time, thats when we noticed the huge puddle of coolant under the car. So the plan for now is a new water pump, & new fan motor. After that, prob new control unit. Also, looks like someone put an aftermarket oil cooler in front of the radiator, where was the stock one located?

HISSIN50 · Feb 26, 2008

A GT does not have a stock oil cooler. If you have an AODE, it might be a trans cooler. Or if it's real small, it might be a PS cooler. You can trace your PS's low side lines (one leaves the rack and goes under the driver side of the radiator and to a PS cooler).

One note on the fan: most of the time the motor separates from the blade ok but like on the last one I did, the blade's bushing (metal) had seized to the motor's output shaft. I broke the fan blade trying to separate it. I mention it as a warning - if you really need this car, you might want to have a spare fan around. I went with a fan from a 3.8L Taurus because they dont seem to have all the meltdown issues that our fans do. They also flow a hair better and are not as thick. The dealership will wipe ya for a fan - a junkyard or ebay will be much easier on the wallet. I dont sweat the used OEM fans too much - they are made to go over 100K miles and most have Siemens motors (a Tier One company).

For now, I'd seriously carry a fire extinguisher with you (we're not kidding). The fuse doesnt seem to blow very often before the wiring harness catches on fire. Depending upon how the fan is failing, you could end up with the motor causing a massive draw.

On your puddle of coolant, do note that coolant expands with regard to heat. If you're running really hot, your overflow might have simply needed to dump excessive coolant out.

The FMS water pump is a nice piece and is about 50 bucks at Summit (same price as parts store stuff and better quality). Stewart Stage one pumps are about 75 and very nice too.

Good luck.

ninjafury · Feb 27, 2008

Progress!!!! Thanks again for all the help. It wouldn't have gone this smooth without these forums & your knowledge & generosity.

We installed a new water pump, mr gasket 180 stat & fan motor. Luckily the fan came off in one piece & we were able to re use it along with the shroud. Now the needle sits religiously on the N. The car sounds & feels great now.

Thanks,

SHANE RED

HISSIN50 · Feb 28, 2008

95WhiteVenom · Feb 29, 2008

Where can I get this DC control unit at JT?
This sounds like an investment I really wanna make.

HISSIN50 · Feb 29, 2008

95WhiteVenom said:
Where can I get this DC control unit at JT?
This sounds like an investment I really wanna make.

Here are ordering instructions. It sounds funny but it's a good thing. It should cut the wait time down (he was getting more orders than he could keep up with). EDIT: He has the same rules for both forums - I just saved the Corral version when I saw it.

Here's an old link with the controllers. I used a FK-35 with our stock fan and with the 3.8L Taurus fan. Brian (the owner) is very very good with recommendations for guys who might upgrade fans, run electric water pumps (some controllers can control pumps too) and so on.

I highly recommend the status LED (it was like ~5 bucks). It changes color as the fan ramps up. And the rheostat is kinda nice to have. I change my target temp from inside the cockpit (in the summer it's lower, in the winter it's higher, etc).

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