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AC Gets Hot...WTH? Pages: 12

jed1154 on Tue May 27, 2008 10:43 AM User is offline

Year: 2005
Make: Ford
Model: F-250
Engine Size: 6.0

My AC seems to do OK at best. However, when i get it down to a temp, and i have to accelerate from a start or to pass or something, the temperature shoots up from 45 to 60, everything fogs up and it gets hot......then it drops back down after a while. Its a diesel engine, so its not vacuum related.

What the hell is the matter with this thing? Any ideas?

mk378 on Tue May 27, 2008 11:05 AM User is offline

Maybe it's designed to drop out the compressor at wide open throttle to get every possible hp to the wheels. If you go somewhat less than wide open does it still do it?

jed1154 on Tue May 27, 2008 11:13 AM User is offline

Yes, sometimes it does it from a stop, just normal acceleration, NOT WOT. I wonder if its a clutch gap issue?

The only other thing it does thats strange is that at 20mph or less the temp gets to 40, then after driving, its at 48 at the coldest. That may be a separate issue altogether.

GM Tech on Tue May 27, 2008 12:22 PM User is offline

sounds like HPCOs high pressure cut-outs- very common for head pressure to rise with increased rpm from an idle...attach a gage set to confirm...

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

jed1154 on Tue May 27, 2008 12:39 PM User is offline

Dam....i guess im going to have to take it to the dealer. Its an intermittent problem, so it should take a qualified tech about.....a week or so to properly diagnose and fix the problem. I didnt want to take it in, but whatever, doesnt cost me anything. Kind of disappointing considering it has 30,000 miles and cost what they sell them for.

HECAT on Tue May 27, 2008 12:57 PM User is offline

Take it back to the dealer under warranty and have it checked out. There are TSB's regarding desiccant failure blocking the orifice tube creating high head pressures, which could be hitting the HPCO.


HECAT: You support the Forum when you consider for your a/c parts.


jed1154 on Tue May 27, 2008 1:03 PM User is offline

Wish me luck. Im gun shy about dealers. Too many "welp, we couldnt reproduce the problem, good luck with all that."

jed1154 on Wed May 28, 2008 1:48 PM User is offline

Dealer said AC cycling switch was bad....they replaced it.

jed1154 on Thu May 29, 2008 4:11 PM User is offline

can you even replace a cycling switch without discharging the system? The service guy says they didnt evac and recharge, but the ticket says they did. Either way, when its sitting still, its cold, when you are driving, you can actually feel the temp go up and down over and over again as you are driving. Very strange. It doesnt get HOT, but it goes from COLD to cool. Cool for a couple seconds....cold for a couple seconds.

Any ideas? Is that normal? The pressures were checked and all checked out ok.

Edited: Thu May 29, 2008 at 4:13 PM by jed1154

94RX-7 on Thu May 29, 2008 5:02 PM User is offline

In most systems you can replace the switch without discharging the system, only a tiny amount of refrigerant is lost.

It is normal for the temperature to go up and down a few degrees if you're rolling down the road, my Ranger does the same thing. What is happening is it is cycling the compressor off to prevent the evaporator from freezing this causes the temperature to rise just a bit.

jed1154 on Thu May 29, 2008 5:25 PM User is offline

ill have to check it on the way home again. Its more than a couple of degrees. I usually cannot notice a couple of degrees. This is more like 5-10 degrees. Its all under warranty, its just a pain in the neck.

94RX-7 on Thu May 29, 2008 7:22 PM User is offline

If the inside of the truck is hot, or it is real hot outside, the temperature difference will be more noticeable. It doesn't cycle the compressor on and off based on air temperature, it does it based on the evaporator pressure.

jed1154 on Mon June 02, 2008 10:38 AM User is offline

Well, it seems to work better, but the best temp i can get out of the vents is about 50 degrees....thats maxed out AC, after 30 mins of driving with 85 degree ambient temps.

I dont understand at all why the system performs so friggin poorly. Its a huge truck, huge engine, huge AC system....what's teh problem? the shop said they 'checked the pressures'. I have a feeling the tech 'checked the pressures' and as long as it was within a range large enough to drive a truck through, it was good. Im thinking abotu taking it back and trying to get them to evacuate and recharge the system.

mk378 on Mon June 02, 2008 10:46 AM User is offline

It should have been opened up to check for the blocked OT problem that HECAT mentioned.

jed1154 on Mon June 02, 2008 11:01 AM User is offline

Its going back. Its a dealership...sometimes i don't think they try very hard.

jed1154 on Tue June 03, 2008 11:15 AM User is offline

When i take it back, is there anything i should tell them that may help them fix it? telling them that "it doesnt cool well" ellicits a "well, its in spec." I don't think 40 degrees out of the vents is too much to ask for the system running 45oz of refrigerant behind a diesel engine.

jed1154 on Thu June 05, 2008 11:33 AM User is offline

OK, i thought the truck was fixed, but yesterday, after a moderate acceleration, the AC went warm. It doesnt do it all the time. Its like the clutch is not engaging very rarely. I put the truck in park and revved it to 2000 rpm, and the compressor is definately cycling so i think we can rule out the clutch gap.

I have had the truck back and driven it for a couple days with no problems. Anyone have any idea what else to have checked, its very difficult to ID intermittent issues like this.

bohica2xo on Thu June 05, 2008 12:58 PM User is offline

Tap the actual clutch wire, and wire in a small test lamp that you can see while driving.

Duplicate the failure, and see if the clutch is getting power when it happens.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

jed1154 on Fri June 13, 2008 2:09 PM User is offline

OK, im about to pick up the truck the second time now.

They said they evacuated and recharged the system and found it was a 'little' low. They also said they repalced the "control head", whatever that is. that was replaced because the system would cool great 90% of the time, but then randomly quit cooling, as though the compressor stopped briefly. This would happen at idle, 2500rpm, 2000 rpm....anytime.

So...i guess we will see.

mk378 on Fri June 13, 2008 2:37 PM User is offline

I think they're talking about the control panel on the dash. Certainly could have caused the problem you experienced.

jed1154 on Fri June 13, 2008 2:53 PM User is offline

Yeah, i just hope it fixes it and doesnt end up being something like a clutch gap issue.

I have no idea how you diagnose a control head though. The service guy said you cant diagnose it, you just replace it. The ticket says it was tested and it had a fault. I asked how low it was and he said he didnt know but the tech said it was enough to cause it to freeze they charge it to the proper volume. The vent temp is at 42-44 on high with 90 degree ambient temps. So, everyone cross their fingers. I know i am.

Edited: Fri June 13, 2008 at 3:46 PM by jed1154

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