Electrical High Speed Fan Working Intermittently, Help!!

Discussion in 'SN95 4.6L Mustang Tech' started by stprorolla49, Sep 2, 2012.

  1. Let me preface this by saying, I have had constant intermittent fan issues for the last 3-4 months. It started out with the car blowing the 50 amp fuse in the engine bay fuse box. I replaced the fuse a few months ago, and had no issues for about 2 months. Then about a month ago, I blew 2 fuses in one day, right after the other. I did some testing, replaced the fan assembly, the low speed fan resistor, and put a new fuse in. The car has been solid up until this last Friday when the high speed fan decided not to come on.

    When I had the car tuned, Kevin set it for low speed to come on at 188 and high speed to come on at 194. Low speed has been working fine but once the car calls for high speed, the fan completely stops. The problem is, this is very intermittent. It could work fine for a month, then not work, then start working again in the same day.

    Here is my Sunday update with my latest diagnostics:

    OK, so let me outline where I am currently at to see if this helps.

    - I start the car cold, fans are obviously not on.
    - I turn the a/c on MAX (car still cold), and the fan comes on as it should.
    - I shut the a/c off, fan shuts off.
    - With the a/c off, car still cold, I unplug the coolant temp sensor on the intake manifold, fan turns on.
    - I plug the coolant temp sensor back in, fans shut off.


    - Wait for car to get to ~188 deg where the tune calls for the low speed fan to come on, which is DOES.
    - Low speed fan runs fine until 194 deg where the tune calls for the high speed fan to come on which is DOES NOT and the fan shuts off completely.
    - At this point I checked the 50 amp fuse in the main engine fuse box and it is NOT blown.


    - Fired the car back up at ~188 deg where the low speed fan should come on which it DOES.
    - 30 seconds later when the car gets to 194 deg when high speed is supposed to come on, it does NOT and the fan shuts off completely.
    - At this point, turning on the a/c on max does NOT turn the fan on, nor does unplugging the coolant temp sensor.

    LS1KILR mentioned the a/c compressor might be going south so I tested that as well with the car COLD.

    - With the car running, I turned the a/c on max, and unplugged the sensor mounted on the a/c line directly underneath my powerpipe. The compressor kicked off. I plugged the sensor back in and audibly heard the compressor kick back on.
    -With the sensor plugged in, I also jiggled it back and forth, up and down as much as I could to see if there was any sort of continuity issue with that plug which there was NOT.

    At this point, from my testing, clearly the wiring to the fans is ok because low speed works all the time, and high speed HAS worked for the last 2 weeks, then only worked intermittently over the last 2 days.

    Someone over on corral suggested it might be the high speed fan relay...

    Can the high speed fan relay be changed by itself, or do you have to change the whole CCRM. From what I understand, the relays are in the CCRM. Also, if I were to change the CCRM, would my fan settings that my tuner programmed change?

    Does this have anything to do with my cycling a/c clutch or whirring sound? I just checked the ground wire going to the fan, because from what I have read, both the a/c high pressure switch and the fan run off the same ground. Resistance on 200ohm setting on my multimeter was between 15 and 17 with the fan working.

    I tested this by turning the car on COLD, turning on the a/c to verify low speed fan was working, unplugged fan clip, and tested resistance on the ground wire.

    Even though resistance is high (Haynes manual says it shouldn't be higher than 5), I don't understand why the low speed fan would still work since both low and high speed run off the same ground wire.

    Tomorrow I will test both power lines for low and high speed fans.

    Also, as mentioned about, during the instances where my high speed fan isnt working, I notice when the a/c is on, the idle fluctuates slightly, there is a slight whirring sound that increases as rpms risem and sometimes the air coming from the vents isnt cold. Not sure if this is related, but it seems to be.

    If anyone can help with this, I'd really appreciate it, this is very frustrating!!!

  2. You are making it harder than it really is. Bottom line, the High speed fan is not running. Every thing else is secondary or the direct result of the high speed fan not running.

    The typical causes are a bad fan motor or bad CCRM. Since the reported symptom is the high speed fan runs sometimes and then blows a fuse, to me that says the fan bearings are BAD. This causes the fan to draw too much current. The problem only gets worse the hotter the fan motor gets. But since the fan has been replaced, that tends to rule out the fan motor.

    Now onto your tests methods. Resistance measurements must be done on an INACTIVE circuit. Any current or voltage on the circuit will make the Ohm meter give an inaccurate reading.

    Regarding the CCRM, for the Mustang, the low speed fan, high speed fan, AC clutch, fuel pump, and PCM power relays are all in the same module. I recommend looking at a re-man CCRM should this turn out to be a CCRM problem (unlikely IMO).

    Sooooooo........ When spun by hand, how to the fan bearings feel? Does the fan spin easily? When the fan stops, is the fan motor hot to the touch? Note, even if the bearing are OK, it's still possible for the fan motor to be bad. Remember there are different internal windings for the HS and LS speeds.

    Is there +12 volts between the fan OG/LB and black wire when the HS fan should be running? If not, focus should be on the CCRM.
  3. Thanks for the info, I was hoping youd chime in. Ive read many of your posts about fan issues so this is great. Someone on SVTP also mentioned the circuit had to be inactive after I posted this. Sorry, I am somewhat of a novice when it comes to testing electronics so please bare with me.

    The fan was replaced with a brand new unit, and from what I have recently felt, the fan bearings seem to be fine. I guess anything is possible though as far as the motor being bad.

    Tomorrow my first order of business is to check the wiring and see what my readings are. I was going to check today but it started to pour. I'll report back with results tomorrow!
  4. Now its throwing PO118 code - Engine Coolant Temperature sensor. I figured, :poo: this controls the fans as well, so I replaced it. No dice, still have a CEL.

    This was around 10am.

    About a half hour ago, I went for a rip to blow off a little steam, and when I came back, the high speed fans were working with the a/c on and the car was at around 200 deg. I shut it off, turned the a/c off, turned it back on, the fans were still working and the CEL was gone. Since I changed the ECT sensor, I had cycled the ignition about 5-6 times. Would that have cleared the code in the car? The factory temp gauge works fine, FWIW.

    NOW, this has happened before with the fans working then not working the next day, but maybe the ECT sensor fixed it. I also tried to unclip the fan clip to check the voltages and burned the :poo: out of my arm on the blower and rad hose. I hate electrical diagnostics!!!
  5. Hmmm, I remember when I forgot to screw in or replace my Temp sensor the High fan came on, I'm thinking burns called it a fail safe mode.

    Hope you solved your "problem."