AC Causes Limp Mode 2000 F-150

Tiny
CRAIG M
  • MEMBER
  • 2000 FORD F-150
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 250,000 MILES
This truck has had this problem for over a decade. The AC works great, but after it runs for about an hour, the engine temp shows normal then jumps to hot and the engine goes into limp mode. The code given is engine temp sensor. It has been replaced several times, but the condition continues. When the ac is not used, the truck never has the problem.
Sunday, August 10th, 2025 AT 10:20 AM

13 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,137 POSTS
To me it sounds like the fan clutch is bad, can you hear it kick in when the engine is running hot and overheating? Can I ask which code is triggered? Here is a guide to help see if the fan clutch is bad or not.

https://www.2carpros.com/articles/fan-clutch-symptoms

This video will show you how to swap the fan clutch out.

https://www.youtube.com/watch?v=PoVQpbkCvtc

Please upload pictures or videos in your response so I can see what is going on.
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Monday, August 11th, 2025 AT 9:16 AM
Tiny
CRAIG M
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The truck is not overheating. The fan is working correctly. The temp gauge goes from normal to pegged and into limp mode. I believe it is connected to the ac wiring, possibly shorting something out.
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Monday, August 11th, 2025 AT 10:04 AM
Tiny
KEN L
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Okay, so the PCM controls the output to the temp gauge. Lets remove the WOT relay to see if it makes a difference. Here is the location. Please let us know what happens.
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Monday, August 11th, 2025 AT 12:44 PM
Tiny
CRAIG M
  • MEMBER
  • 13 POSTS
I will try that. Does it make a difference if it’s never happened during wot?
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Monday, August 11th, 2025 AT 2:28 PM
Tiny
KEN L
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No, if this relay is shorted it will back feed into the PCM causing the issue you are having.
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Tuesday, August 12th, 2025 AT 8:26 AM
Tiny
CRAIG M
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  • 13 POSTS
I ran the ac for awhile then pulled out the wot relay. The compressor quit working and when I pulled the relay out it was very hot.
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Tuesday, August 12th, 2025 AT 4:41 PM
Tiny
KEN L
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  • 54,137 POSTS
Okay, you may have an AC compressor coil that is starting to short out, I would use a voltmeter to test the coil, the A/C compressor clutch coil should typically measure between about 3.5 and 4.5 ohms when tested at room temperature. Here is a guide to help you.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Please go over this guide and get back to us.

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Wednesday, August 13th, 2025 AT 10:11 AM
Tiny
CRAIG M
  • MEMBER
  • 13 POSTS
Coil connection shows 3.8 ohms.
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Thursday, August 14th, 2025 AT 9:52 AM
Tiny
KEN L
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Okay, so that seems okay but this test is not 100% accurate. Can you put 12 volts to the coil to see if it closes? Lets try this, leave the AC compressor unplugged but then turn the system on for an hour to see if the problem goes away. My thought is when the coil gets hot is shorts out causing the issue.
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Friday, August 15th, 2025 AT 10:58 AM
Tiny
CRAIG M
  • MEMBER
  • 13 POSTS
I ran it with the compressor disconnected and the air turned on for4 hours. It did not shut down and go into limp mode. You’re probably correct about the ac coil wiring. Should I replace just the coil or whole clutch assembly? Or could it possibly be the wire or connector to the coil?
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Sunday, August 17th, 2025 AT 2:24 PM
Tiny
KEN L
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The problem is the clutch coil, I would see if you can find one which you can replace separately. If not you will need to replace the compressor, this video will show you how to vacuum down and recharge the system.

https://www.youtube.com/watch?v=4EqdrBVb0sY

Let us know how it goes
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Monday, August 18th, 2025 AT 10:27 AM
Tiny
CRAIG M
  • MEMBER
  • 13 POSTS
I ordered a motorcraft coil. I will let you know how it works out.
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Monday, August 18th, 2025 AT 10:57 AM
Tiny
KEN L
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Sounds good, it would be great if we could fix it after all these years :)
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Monday, August 18th, 2025 AT 10:58 AM

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