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A/C Works Intermittently

Tiny
TECH2020
  • MEMBER
  • 2009 FORD F-150
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 130,000 MILES
My stepson`s truck the A/C was repaired recently, it worked well for a couple weeks but is now intermittent. The system always blows air but is cold only sometimes.

What would be the most likely causes of this kind of issue? We plan on having the coolant pressures checked and could replace the pressure sensors if need be if we can identify them. I can use a DVM to check resistances and voltages.

Thanks!
Tom
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Tuesday, June 14th, 2022 AT 5:16 PM

7 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

When you don't have cold air, is the compressor still running? If it isn't, the first thing to try is adding Freon. It may be low. Here is a link that shows how that is done:

https://www.2carpros.com/articles/air-conditioner-how-to-add-freon

If the compressor is running, it could be related to the blend air door actuator. Does the truck have dual climate control?

Let me know. If it does have dual climate control, I wouldn't think both sides would stop working at the same time.

Let me know.

Joe
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Tuesday, June 14th, 2022 AT 10:05 PM
Tiny
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Hi Joe,

The truck does not have dual climate control. Recent repairs included new lines and recharging. My stepson stated the high and low pressures checked good, but the compressor clutch is not engaged. Would this indicate a bad high- or low-pressure sensor?

Thanks, Tom
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Thursday, June 16th, 2022 AT 5:59 PM
Tiny
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Hi,

If the compressor clutch isn't engaged, it wouldn't work. Also, by chance do you know what the pressures were?

As far as the compressor is concerned, a pressure switch will prevent it from operating if the limits set in the sensor are exceeded. What would need to be done is when it doesn't engage, you could bypass one at a time (high pressure and low-pressure switch) to see if it allows the compressor to operate.

Or, if the compressor clutch could be affected by a faulty compressor relay. It's located under the hood on the left side in the Auxiliary relay box. You may want to switch it with a different relay having the same part number. If there isn't one, here is a link that explains how to test a relay:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Let me know.

Joe
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Thursday, June 16th, 2022 AT 10:18 PM
Tiny
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Joe,

My stepson did not take the pressure readings, I believe someone else told him they were okay, so we don't have the values. He also stated he has already tried switching a relay for the compressor and bypassed the pressure sensors. He is out of ideas, so his boss (works at a tire shop, knows lots of locals) talked to an A/C repair shop for him in the area and they will be looking at it next week. He needs it done ASAP, and has little time to do it himself now. I will post here what we learn.
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Friday, June 17th, 2022 AT 7:00 AM
Tiny
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Hi,

Thank you for the update. Let me know what you find. I'm interested in knowing.

Take care,

Joe
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Friday, June 17th, 2022 AT 7:12 PM
Tiny
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HI Joe,

My stepson got his A/C repaired today. It was a bad connector at one of the pressure sensors. So, if the pressure sensors were jumped out at the connectors it is possible that would not have uncovered the problem. For situations like this is there an easy way to jump out the sensor input closer to the computer board(s) thus eliminate this possibility?

Thanks, Tom
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Wednesday, June 22nd, 2022 AT 8:09 PM
Tiny
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Hi,

The sensor connector is simply disconnected, and a jumper put between the terminals. And yes, that likely would have identified the issue unless the wiring at the connector was damaged and not complete.

As far as doing it before the sensor, you would need to trace the wiring back as far as you would want and check it.

I thank you for the update. I'm glad to hear the problem has been resolved.

Let me know if you have other questions and please feel free to come back anytime in the future.

Take care,

Joe
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Wednesday, June 22nd, 2022 AT 8:42 PM

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