Cooling fan behavior

[paheff]

I have a cracked cooling fan blade that is hitting the shroud. I first noticed it the day before yesterday as I was about to turn the ignition off after driving 20 minutes to get home . When I opened the hood, I noticed that the fan was cycling on with the A/C, but was cycling off after 10 seconds or so, and well in advance of the A/C. I'm embarrassed to say, on that day I did not notice the coolant temp.
Yesterday, on the drive home I noticed that sitting in traffic, idling, the A/C was not cooling. The coolant temp at that point was nearly pegged on H. Traffic ahead was moving, so I got rolling and every thing returned to normal. In the little bit of stop and go after I got off the interstate, same deal. Temp began to rise, no A/C at idle, or more accurately while not moving.
Got home, raised the hood, checked the coolant ( full ) and noticed that the only time the cooling fan was on was when the compressor would cycle on, and then only for 10 seconds or so.
My wife drives this car on a daily basis, but since she's out of town, I was driving it. I called her and she said that the A/C had been fine in traffic, so, I am guessing that this is a new development.
I guess this is a long winded way of asking, what is the normal operation of the cooling fan? I understand that is is a variable speed motor, but shouldn't it be full on any time the A/C clutch is engaged, or when at idle with the engine slightly above normal operating temp? I need to replace the fan blade, but I'm suspicious of the way the motor is behaving.

[paheff]

Bled air from cooling system. The cooling fan only comes on for 10 sec or so at a time, A/C on or off. Could the fan rubbing the shroud be causing the motor to go out on overload? It only rubs when it gets up to speed. 15 min idling in the driveway, fan on 10 sec out of every minute or two, temp normal. Got in to drive it, turned on A/C, backed out of driveway, temp immediately began to rise. Parked it, getting into truck to go to work.

[Local Boy]

If I'm not mistaken...The fan should go on at a certain temp. and stay on until the engine temp. drops below that predetermined temp.

Your assumption sounds plausable...The fan could be over heating from contacting the shroud. Otherwise, the computer controls when (pre-determined temp. setting) the fan comes on...Do you have a tune?

How did the fan get damaged?

ALOHA

[jgc61sr2002]

I thought the fan can on in the AC mode.

[Local Boy]

If I understand correctly, My A.A tune turns on the fan sooner (ie: at a lower engine temp.) to compensate for a more advanced timming...which results in heat, regardless if the A/C is on or not... I don't see why the fan would be activeated by just the A/C...
I'M I MISSING SOMETHING? Where did you get that information...I would be very interested to learn why this would be the case...Please help me understand...ALOHA

[paheff]

If I'm not mistaken...The fan should go on at a certain temp. and stay on until the engine temp. drops below that predetermined temp.

Your assumption sounds plausable...The fan could be over heating from contacting the shroud. Otherwise, the computer controls when (pre-determined temp. setting) the fan comes on...Do you have a tune?

How did the fan get damaged?

ALOHA

Yes Dennis tuned it about 2 years ago, and BTW that was money VERY well spent.. As for the fan damage, I am assuming heat/stress/defect since it does not appear to have sustained any kind of damage. It is the outer ring that joins the ends of the blades that is cracked and it contacts the shroud when it gets up to a certain speed due to centrfugal force. What I need to know before I try to locate a blade is, with the way it is behaving, is it possible that the 10 or so second run time is due to the ECM seeing higher than normal current and shutting the fan off, causing the rest of the problems I described?

[MM_BKK]

The fan will ususally turn on when the A/C compressor is running so that it can remove the heat from the condenser that is full of hot, high pressure Freon gas and causing it to condense to liquid state so that it can evaporate in the evaporator coil so that you will have cool air blowing out of the register.

Have you notice that the A/C compressor for a central air system has a big fan blowing on the condenser coil. That's why our fan needs to run when the compressor is engaged.

[Local Boy]

That's very true...But wouldn't it (the fan) stay on , if the engine is hot, even if you turn off the A/C?...ALOHA

[MM_BKK]

With the A/C off, the fan will run variable speed depending how hot the engine is. I think the coolant temps has to be somewhere around 220* for it to run at full speed. My Scanguage II would display a range of temperature anywhere from 180* to 220* and the dash needle would hardly move from about the 20mph position. Don't trust the temp needle!

I found that running the A/C will actually keep the engine cooler, because when the compressor is engaged, the fan will run full speed.

[paheff]

With the A/C off, the fan will run variable speed depending how hot the engine is. I think the coolant temps has to be somewhere around 220* for it to run at full speed. My Scanguage II would display a range of temperature anywhere from 180* to 220* and the dash needle would hardly move from about the 20mph position. Don't trust the temp needle!

I found that running the A/C will actually keep the engine cooler, because when the compressor is engaged, the fan will run full speed.

Thank you. That is how I believed that the fan should work. Now that you have confirmed that, I now believe that the added resistance caused by the fan hitting the shroud is causing the fan motor to shut off either by the computer due to high current or internal overload.

[Tom Doan]

Had the same problem, do not waste your time and a motor messing with it, replace ONLY. Tom

[paheff]

Had the same problem, do not waste your time and a motor messing with it, replace ONLY. Tom

You had similar problems and you replaced the whole assy? I am about to resign myself to doing the same since like you said I,m wasting alot of time trying to save a few $$. Thanks.

[Local Boy]

There you go MM BKK, that's what I was refering to....ALOHA

BTW: AA's tune will bring the fan on earlier @160* to compensate for the advanced timming.

[Drewstang]

I just had the same problem 2 weeks ago. You cannot replace just the fan blade. The whole unit (shroud, motor, and blade) must be replaced. The reason the fan blade borke was the motor is out of round. That means you need a new motor as well. I went to my local Napa and got a Motorcraft replacement and it ran me $240.