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A/C blows hot when idling

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Old 07-28-2015, 03:49 PM   #1
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Default A/C blows hot when idling

'06 STX 4.6L

Just bought this truck and I'm pretty unfamiliar with how all the systems work.

A/C blows OK when going down the road. It should probably be colder even at highway speeds. But when stopped at a light it blows hot air. I can rev it up at idle and it gets cooler.

I took it to a shop and they tried to run an A/C analysis on it and said they couldn't get several signals that they need to run the analysis. They suggested an electrical shop that could find the faulty wiring preventing the signals.

I will confess, I'm not an expert on cars, especially the newer ones, however, I fail to see how a wiring issue could cause this. My best guess would lean towards a compressor clutch going bad maybe (not turning fast enough at idle).

The truck also has the brake warning light on all the time even though there aren't any issues with the truck. I think that led them to just assume it has many wiring issues causing all the problems.

Any thoughts, suggestions? Thanks in advance!
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Old 07-28-2015, 06:33 PM   #2
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Sounded like your engine fan's clutch is not engaging, time for new clutch or you can go with 2010 F150 electric fan conversion.
I did and very happy with it. It is a little costly though.
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Old 07-28-2015, 08:10 PM   #3
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Ouch! That's Pricey.

I'll look into the fan clutch. Wouldn't the engine run hot in that case? Water temps are fine.
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Old 07-28-2015, 10:39 PM   #4
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Quote:
Originally Posted by B_Stewart View Post
Ouch! That's Pricey.

I'll look into the fan clutch. Wouldn't the engine run hot in that case? Water temps are fine.
In a way you are right, but do you have a programmer hook up like Edge Evo so you can see live coolant temperature? I wouldn't trust those dummy gauges, some of them are dampen. A normal operating temp is around 195 F.

Our trucks are getting old and the A/C refrigerant will leak. You need a friend with equipment to hook it up and check it out.
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Old 07-29-2015, 04:49 AM   #5
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Poor A/C operation at idle is very common on the 04 to 08 F150 models. The clutch fan simply does not pull enough air through the front radiator and A/C condenser while idling. Compound it with any accessories you may have in the grill (light bars), and this can make it worse.
Check the fan clutch for operation; see if the fan is spinning at idle. The 4.6 and 5.4 engines use an electric clutch. Many have converted to an e-fan setup (I have), and the A/C blows much colder at idle. For me, it was a Mark VIII e-fan setup with a Flex-O-Lite controller. I have under 200 bucks invested with this conversion.
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Old 07-29-2015, 08:42 AM   #6
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I'll definitely make the fan clutch my next check. This thing is bone stock. The only thing added to this thing is a Flex bed cover. Roll up windows, manual locks, 4WD shifter on the floor.....just the basics!

$200 sounds reasonable. I'll do some searching and look into that. I guess if it's barely getting by when it's working great, then it doesn't have to lose much performance to blow completely hot air at idle. I never would have thought to check that to be honest.

Thanks for the help guys, I'll run this to ground and check back in!
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Old 07-29-2015, 11:07 AM   #7
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Default A/C blows hot when idling

You can test your compressor clutch pretty easy, but it can be dangerous. If you think it's gone bad, you can put a glove on and slowly lay your fingers on the blades while it's spinning. If it knocks your hand back, the clutch works fine. If you are able to stop it, then it's gone bad. BE EXTREMELY CAREFUL IF YOU TRY THIS!!
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Old 07-29-2015, 06:09 PM   #8
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Default A/C blows hot when idling

Quote:
Originally Posted by slackattack View Post
You can test your compressor clutch pretty easy, but it can be dangerous. If you think it's gone bad, you can put a glove on and slowly lay your fingers on the blades while it's spinning. If it knocks your hand back, the clutch works fine. If you are able to stop it, then it's gone bad. BE EXTREMELY CAREFUL IF YOU TRY THIS!!
Yea, that sounds pretty dangerous. I think I would prefer a broom stick or something, anything other than my fingers!
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Old 07-29-2015, 07:21 PM   #9
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Ok, so here's where I'm at.

With truck at idle, I took a very thin sheet of bubble wrap and layed it against the condenser. It didn't even have enough airflow to hold it in place. Then I layed the bubble wrap over the transmission?oil? cooler and revved the engine a little. Slowly it pulled the bubble wrap onto the condensor and held it there, then slowly it would loosen up and fall back off as the RPMs settled down. It wasn't a calibrated piece of bubble wrap, but I think it indicated low air flow!

I was able to stop the fan blade with my hand with relative ease. It was a lot easier than stopping a ceiling fan. Wasn't immediate (maybe 4-5 seconds), but did slow and stop without a lot of pressure.

So, in short, I think you guys nailed it.

It would be nice to have someone confirm how much air pulls from a good one. Will it hold a piece of paper on the condenser at idle? Will it pull a piece of paper to it at idle? Lots of traffic to sit in here, so I'm going to change it anyhow. Will definitely look into the e-fan thing but will just throw a clutch on for now.
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Old Yesterday, 06:48 AM   #10
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If you ever thinking electric fan conversion go with twin 2010 f150 fan.
Here is a demonstration from one of our member posted on YouTube.

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