2004 Mustang GT Overheating

[Snow White 2v]

I have a 2004 GT with full bolt ons. It’s been getting really hot in the city (210-225). Whenever I’m on the highway temps drop to about 185. I’ve discovered it’s because my fan isn’t running properly, if at all, when overheating. My car will be at 225 degrees sitting still with the fan not running. Yet when I turn on the ac eventually it comes on but it doesn’t seem to stay on.

I’ve replaced the thermostat, water pump, and coolant temp gauge. It doesn’t seem to be leaking from anywhere because the coolant levels stay reasonable. I’m nearly positive it’s because of the fan not coming on. Any ideas of what to check and where to start looking?

 

[tsemmett]

Based on what you're describing, I'm not sure it's your fan. When mine failed to come on, it boiled over on me (I was stuck in traffic at the time). But, between the fan and some A/C troubleshooting I had last year, I've touched pretty much everything related to this, so I offer some advice here.

If you have a tuner, you might check and see if you can adjust the fan temps (set them to come on sooner and see if they do), or even test the fan. Otherwise, you'll need to do some wiring diagnosis.

If you want to confirm whether or not your fan is the issue, I would do something like:

1. Test the fan itself with a battery. Red/Orange wire is low speed (+12v), Orange/Light Blue is high (+12v), and black is ground. Connect one of the +12v pin and the ground to a battery to confirm it comes on, then do the same with the other. It's a high amp circuit (50A), so don't hold it for long, and don't connect both +12v pins at the same time.

2. If the fan comes on, move to the wiring. Is the connector damaged? I've heard of them melting, but in my case, one of the pins backed out (the seal on the back was sticking out). If it looks good, turn the car on with the AC running and unplug the fan to test for voltage. You should have at least 12V between the high speed and ground pins. Drive the car around and get it hot enough that you think it should come on, then do the same for the low speed.

3. If there is no power at one of both of the fan inputs, unplug your CCRM and test for a break between it and the fan. The CCRM is under the passenger fender (pull the tire and pull back the fender liner, you'll see it towards the top), and has an odd side (5.5mm) retaining bolt on the plug.

Pins 1 and 2 (Red/Orange) should be your low speed output (+12v), Pins 6 and 7 (Orange/Light Blue) should be high speed. Use a multimeter to tone test between the CCRM connector and the fan connector (both pins for each speed should connect to the wire for that speed at the fan). That will confirm the wiring between the two is okay.

4. Confirm the CCRM is getting power from the fan circuit. Pins 3 and 4 (Black/Orange) should be input (+12v). Test for voltage between them and Pin 15 (Black/White), which is the CCRM's ground.

5. If all these are good, the only other test I can think of would be to test the internal relays on the CCRM. This I haven't tried, but based on the wiring diagram, you should be able to ground pin 15 and apply power to pin 14 (Dark Blue) to engage the low speed relay (at which point you should be able to tone test between Pins 1/2 and Pins 3/4), and then apply power to pin 17 (Light Green/Purple) to engage the high speed relay (connecting pins 6/7 to 3/4).

 

[wmburns]

My vote. The low speed fan is not working. The reason that that there's a delay when the AC is on is because the high speed fan runs when the AC head pressure is above a certain limit. So because the low speed fan isn't working, it's only a matter of time before the AC head pressure will go through the roof thus making the high speed fan run.

Further if asking for an educated guess, the low speed ballast resister has failed. But If this were my car, I would test and confirm exactly what's wrong before replacing any parts.

 

[Snow White 2v]

Thank you very much for the informative posts guys I really appreciate it! I’ll start diagnosing and see what I can find.

 

[Snow White 2v]

My vote. The low speed fan is not working. The reason that that there's a delay when the AC is on is because the high speed fan runs when the AC head pressure is above a certain limit. So because the low speed fan isn't working, it's only a matter of time before the AC head pressure will go through the roof thus making the high speed fan run.

Further if asking for an educated guess, the low speed ballast resister has failed. But If this were my car, I would test and confirm exactly what's wrong before replacing any parts.

Where is the low speed ballast resistor located and where could I purchase it? Can’t find anything about it online. Just the blower motor resistor.

 

[wmburns]

Where is the low speed ballast resistor located and where could I purchase it? Can’t find anything about it online. Just the blower motor resistor.

A ballast resister is just another name for a heavy duty resister used to drop voltage and slow the fan down. As to where it's located just follow the wire from the fan connector. Do you see fat spot in the wire? Usually someplace where the fan can also blow cooling air over the resister.

Have you tested to see IF both speed fans work when driven directly from the battery with a fused jumper?

It's also possible to solve the problem by just buying a whole new fan assembly which will come with a new resister.