Highway AC issue

[Andrewp65]

2011 2.3 auto, just picked this truck up, runs and drives good. AC works great when driving around town, nice and cold, but when you hit the highway and get over 50 plus, it quits cooling. It blows but not cooling. Let it sit for a bit and back cooling but get it up to speed and same issue. Any info or ideas? Thanks

 

[pentode]

Low refrigerant charge?

 

[SenorNoob]

It shouldn't be, but any possibility you're hitting the WOT cutoff too soon?

 

[pjtoledo]

when idling what is the AC cycling time? clutch on-off
also try it at 2000 rpms in neutral.

 

[Andrewp65]

The WOT cutoff is a new one on me, but found an article on it, sounds like the issue. Not getting any codes, do you know about where it is located?

 

[pjtoledo]

PCM gets info from throttle position sensor, then decides to invoke WOT cutout.

 

[Andrewp65]

So the PCM is just not allowing the AC to come back on after slowing down because it’s the issue or it is getting bad info from the TPS? I do appreciate the help, It gets warm in South Mississippi

 

[SenorNoob]

Is there a relay in 2011? I'd expect if the TPS was that far off you'd have other problems.

 

[lowspeedpursuit]

About a millions years difference, so not sure if it's relevant, but the "WOT" cutoff on my '94 isn't throttle-based; it's about 4k RPM. It's not that weird to hit it on the highway in the Lima in a situation where I can't use OD, but that part's probably not relevant to you with the newer engine at 50mph.

Also consider the PCM cuts A/C if it thinks the engine's overheating, which has bitten me in a 2010 van with the Duratec. It would also be weird for that to rear its head at a particular speed, but it's worth investigating.

 

[Andrewp65]

If I understand correctly, the WOT is controlled by the PCM, in a 2011 2.3, no relay. Is it getting a faulty signal from the TPS and not allowing it to cut the AC back on, even after a few minutes or slowing down. I thought I might have a Vaccum issue but the AC works perfectly during city driving. No codes found, thought about trying the TPS just to rule it out.

 

[SenorNoob]

Is it possible the AC clutch coil goes open after things warm up? Should be easy enough to test if you can get the to the connector quickly after a stop.

 

[Andrewp65]

I had been driving for 20 minutes in town, AC working great, nice and cold. No issues till you hit the highway and get about 50, then lukewarm breeze. It never quit, just won’t cool. Got in it this morning, ran perfect but in city traffic, only got around 40 mph, no issues.

 

[RobbieD]

Spit-balling here.

Have you ruled out, that the HVAC system is not getting enough vacuum at highway speeds?

Could it be that the AC may be getting blocked out from the cab, if the HVAC lacks the vacuum to set the ducting doors properly?

Disclaimer: I have no experience with the later model trucks; especially as late as an '11. So I don't know how much yours uses vacuum to set its ducting.

Early trucks are different (simpler- less vacuum servos I suspect); but on one of mine, a vacuum leak feeding the HVAC control made my defrost drop out at high-RPM cruise or pulling a long hill. Puzzling at first, and kind of an eye-opener once I figured it out.