Why does Engine cooling fan quickly cycle on and off. - Mustang Evolution

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Old 08-14-2019, 12:31 PM   #1
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Question Why does Engine cooling fan quickly cycle on and off.

I remade this thread to further diagnose the exact issue and to make it more organized. Took it to a local shop called tireman and they did an AC service where the claim that the level was low and there may be a leak. Its a 2011 with 25k miles I only drive during the summer months and store it during the winter so I would be surprised and honestly doubt it was even low because it was working fine and blowing cold air.

Idk how it could be low but they put dye in the new stuff. So they evacuated the system weighed it and then refilled to proper spec. But the short cycling issue still remains which I was afraid would happen. Now I feel like I wasted $85. On top of that they claim it will cost $110 to diagnose. The compressor seems to not be cycling as much but the radiator/blower fan is literally turning on and off every 15 seconds. Video linked below.

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Old 08-14-2019, 01:31 PM   #2
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There is so much conflicting information, some people say the cycling is a bad sign and indicates a bigger issue within the AC system as a whole. This link here https://www.thetireman.com/Heating-and-Cooling.aspx claims "Some warning symptoms are: Electric engine cooling fan quickly cycles on and off" Other people say this is normal operation including some dealerships.

This website here https://www.aa1car.com/library/electric_cooling_fan.htm claims "so the fan does not come on until the engine reaches normal operating temperature (195 to 215 degrees). The fan will then cycle on and off as needed to maintain the coolant temperature"

So I guess it might be possible that this is normal? I have no clue. Two different people both with a 2011 and 2012 claim their fans do not cycle. It sure does not sound normal, the car seems to be boged-down every time this cycling happens and it does not sound good on the engine. I am afraid this is going to prematurely wear out parts leading to a more expensive repair. But with all these repair shops just taking random guesses at what might be wrong that is a sure way to waste a lot of money very fast.

I guess at this point I may just let it go and see what happens, some people say if its aint broke dont fix it. The AC for the most part blows cold, I think after tireman serviced it it is actually blowing warmer than previously so I really feel screwed. I wish I would have never even taken it in to be checked out.
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Old 08-14-2019, 02:04 PM   #3
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I believe that the fan works differently when AC or defrost is on because the compressor/evaporator needs a fan no matter what the temp of the coolant. I know my fan comes on almost as soon as it is started with AC on and stays on. Of course this is in the 90 degree heat of Florida. But if my AC is off the fan does not come on until the engine is warm.
It is normal for the compressor to cycle so does your fan cycle with it? That might explain the bogging.
Edit.
I think I might have found your problem. A bad cooling fan resistor. Check this out..
https://www.allfordmustangs.com/foru...eration-c.html
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Old 08-14-2019, 02:17 PM   #4
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Originally Posted by iguanaman3 View Post
I believe that the fan works differently when AC or defrost is on because the compressor/evaporator needs a fan no matter what the temp of the coolant. I know my fan comes on almost as soon as it is started with AC on and stays on. Of course this is in the 90 degree heat of Florida. But if my AC is off the fan does not come on until the engine is warm.
It is normal for the compressor to cycle so does your fan cycle with it? That might explain the bogging.
Yes the fan cycles with the compressor. I just basically ran my car trying to over heat it trying to make the fan kick on with no AC, its 84 here and I did not turn the AC on and drove the car for well over 10min at times at full throttle and I guess I have the best working coolant in the world because the temperature gauge stayed right below the half way mark and the fan NEVER turned on once. I even sat in the drive way for 5min after I got home and at multiple lights waiting for the fan to kick on.

But as soon as I press the AC power button to turn it on there is a loud audible noise and vibration and the compressor and fan start cycling every 15-30 seconds like clock work and every time they turn on the car noticeably bogs down and vibrates and the rpm gauge fluctuates.

I may need to start looking into the relay switches and gauges because I feel like something is getting a false reading. Anyone I have talked to that has the same year make & model states that their fans stay on so that is why I think something is wrong.
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Old 08-14-2019, 03:02 PM   #5
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The problem is your fan has 2 speeds and low speed should turn on and stay on as soon as you start your engine with AC on. You only have high speed which only kicks in when the pressure gets too high in the compressor then the pressure goes down and it kicks off. It's a bad cooling fan resistor that has no low speed. Check this link. He has a 2005 but the system works the same.
https://www.allfordmustangs.com/foru...eration-c.html
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Old 08-14-2019, 06:49 PM   #6
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Here is a better video both compressor and fan seem to be short cycling and this does not seem to be working properly and I am afraid will lead to premature wear or component failures...

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Old 08-14-2019, 06:57 PM   #7
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Originally Posted by iguanaman3 View Post
The problem is your fan has 2 speeds and low speed should turn on and stay on as soon as you start your engine with AC on. You only have high speed which only kicks in when the pressure gets too high in the compressor then the pressure goes down and it kicks off. It's a bad cooling fan resistor that has no low speed. Check this link. He has a 2005 but the system works the same.
https://www.allfordmustangs.com/foru...eration-c.html

This sounds like a possible solution. I am taking it to a different shop tomorrow.
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Old 08-14-2019, 07:53 PM   #8
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It fits all the symptoms including the bogging when the compressor turns on due to the high pressure. That cannot be good for compressor life. That also does not happen when my compressor cycles. It also could be why your fan did not turn on when you tested it. High speed probably does not come on until you are overheating.
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Old 08-15-2019, 05:26 AM   #9
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I thought my fan ran all the time because every time I checked it my A/C was on. This morning it's a cool 67 degrees outside. After reading this Thread, I started my Mustang (first start of the day) with the A/C 'off'. The fan did not come on, I let it run for a couple minutes then shut the motor off. I then restarted the motor with the A/C on. The fan came on, the motor was still cold. I then shut the motor off and turned the A/C off and started the motor again. The fan didn't come on. So I guess it's safe to say, the fan runs all the time when your A/C is on
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Old 08-19-2019, 10:02 AM   #10
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Originally Posted by iguanaman3 View Post
It fits all the symptoms including the bogging when the compressor turns on due to the high pressure. That cannot be good for compressor life. That also does not happen when my compressor cycles. It also could be why your fan did not turn on when you tested it. High speed probably does not come on until you are overheating.

Hey iguanaman3 I really appreciate your responses and information I think you are probably correct because after I took it to the 2nd shop they told me that only the high speed was turning on with the high pressure switch relay or something like that and the low pressure switch would turn on as well but the fan would not turn on when it should. I mentioned the possible resistor issue to them but they were unable to diagnose it any further. So it sounds like I will need to purchase a new resistor but from where?

oh and the fan eventually did turn on to prevent over heating yesterday.
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Old 08-19-2019, 03:26 PM   #11
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I looked for the part and for some reason it is outrageously priced at $150 or more while a new Motorcraft complete fan assembly which includes the speed resistor is $165? I guess I would go for replacing the entire fan for $15 more. Other brands of replacement fan assemblies are less than $100 and include the resistor too. Here's a link to the part by itself. You would think it is made of gold or something. Tasca claims the list price is $227!
https://www.tascaparts.com/oem-parts...3a/?c=YT1mb3Jk
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