Strange A/C Problem

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Strange A/C Problem

Post by Ducky's Dad » Wed Sep 05, 2018 9:59 pm

Not very off-roady, but I am suddenly having a goofy issue with my air conditioning on my '05. A/C has always been great on this truck, but last week in AZ it started acting up. Using an infrared thermometer to check vent temps while driving, I get readings from 17F (freakishly low) to 94F (like driving a convection oven). All of this with the A/C set to max cold/recirculate/max blower speed. At low speeds and moderate engine loads, the A/C is fine and you'd never know there is a problem. At highway speeds up to and way above the speed limits, the A/C blows hot and cold. Moderately cold when just cruising at 70 on level ground, but when accelerating up an on-ramp or passing or even climbing a moderate grade, the vent temp climbs rapidly until I back off the throttle and then things start to cool off again. The 94F vent reading was at highway speed with an outside temp of 97F. Had codes checked this morning and there was nothing that looked related to the A/C. Having pressures checked tomorrow. It will idle and blow cold all day long, until it gets out on the road. I have heard that these trucks sometimes have intermittent A/C fan failures that cause the compressor to quit until the fan starts up again, but fan is fine when it's parked with the hood up. I am certainly no A/C expert, but I suspect the problem is in the sensors or calibration of whatever circuit shuts off the compressor when the engine is under heavy load. Seems like it is sensing moderate loads as heavy loads. Anyone seen anything like this or have a better diagnosis? It was 117F on Sunday and a miserable drive.

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Re: Strange A/C Problem

Post by DamageWagon » Wed Sep 05, 2018 10:13 pm

I would not expect it to be speed dependent but the 3rd gens have their blend doors break and it’s possible outside air is blowing over your heater core. No clue why throttle would have anything to do with AC response. 17F is freakishly cold for auto AC, I didn’t think you could get it to go below freezing on an average day. Might confirm that number.

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Re: Strange A/C Problem

Post by RustyPW » Wed Sep 05, 2018 11:54 pm

Wait and see what the pressure numbers are. Could be just low on freon.
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Re: Strange A/C Problem

Post by Bill2014 » Thu Sep 06, 2018 7:59 am

I agree that it may be low on charge (or sensing a low charge) and turning the compressor off. On max, I believe the compressor is commanded to stay on - so if it really is cycling then look for a charge related issue. If the compressor is not cycling, then it's likely something with the air ducting flappers which will show up in a big way at high speeds (not high engine loads)
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Re: Strange A/C Problem

Post by Retired BLM Rig » Thu Sep 06, 2018 9:46 am

Weird things can happen with a low charge, I would start there. However it could also be overcharged causing the high pressure limit switch to trip. Ambient temperature plays a big part on high side pressure. I see more overcharged systems since auto parts stores started selling "DIY freon kits".

On another note: Most modern computer systems command all accessories off under wide open throttle conditions, (A/C & alternator), to minimize drag on the engine. They want all the horsepower going to the wheels, not driving accessories. Since a WOT scenario usually only lasts a few seconds, it generally goes unnoticed by the driver. Each vehicle is different as to the percentage of throttle this happens at.

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Re: Strange A/C Problem

Post by Bill2014 » Thu Sep 06, 2018 11:58 am

Retired BLM Rig wrote:
Thu Sep 06, 2018 9:46 am
Weird things can happen with a low charge, I would start there. However it could also be overcharged causing the high pressure limit switch to trip. Ambient temperature plays a big part on high side pressure. I see more overcharged systems since auto parts stores started selling "DIY freon kits".
Doubt the OP is overcharged. Since this "suddenly" happened and I'm sure he would have mentioned dicking with the charge...
Retired BLM Rig wrote:
Thu Sep 06, 2018 9:46 am
On another note: Most modern computer systems command all accessories off under wide open throttle conditions, (A/C & alternator), to minimize drag on the engine. They want all the horsepower going to the wheels, not driving accessories. Since a WOT scenario usually only lasts a few seconds, it generally goes unnoticed by the driver. Each vehicle is different as to the percentage of throttle this happens at.
Interesting - does the latest gen Power Wagon do this? would a 2005 Power Wagon do this?

I do know that old vehicles with vacuum actuators would sometime close the vents at WOT - but ours aren't vacuum controlled :D
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Re: Strange A/C Problem

Post by Ducky's Dad » Thu Sep 06, 2018 12:11 pm

Since a WOT scenario usually only lasts a few seconds, it generally goes unnoticed by the driver.
When I first noticed the problem on Friday, I thought it was my imagination. When I got to Yuma I dug out the infrared to see if my perceptions were correct and it was even worse than I thought. Re checking calibrations, I have another infrared to compare against, but not with me. Pretty sure the high readings are accurate because when I had the 94F vent temp, the outside air at 97F felt the same. Re the 17F low reading, that was yesterday and it only stayed there for a brief moment. Those low readings only occur when the truck is started from cold after being parked for a few hours. When I got the 17F, ambient was around 82F. In Yuma I was seeing 20F to 26F after startup with ambients in the 86F to 110F range. Once the system has been running for a few minutes, it seems to bounce around the mid-30s, but will drop to high 20s or jump to mid 70s without much provocation. When I get on the throttle for more than a few seconds, I can feel the temps rising and it touched 90 several times on moderate grades. The 94F at the outlet was on a fairly long but not too steep grade on I-8 going over the mountains from Dome Valley into Yuma, maybe 3000 feet elevation. Hit the crest, backed off the throttle, got cool air again coasting down the other side. I can usually hear the blend doors and nothing sounds odd about them right now. Have any of you installed the Dorman blend door repair kit for the 3Gs?

I have not added charge because I din't want to blow seals when the system was working at least part time. Yuma is a bitch this time of year. I'm home now, truck is in the shop but it is, of course, working just fine there.

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Re: Strange A/C Problem

Post by Retired BLM Rig » Fri Sep 07, 2018 2:55 am

Bill2014 wrote:Doubt the OP is overcharged. Since this "suddenly" happened and I'm sure he would have mentioned dicking with the charge...
As I said earlier, ambient temperature plays a big part on high side pressure. There is a direct correlation between the two. If it's 80º outside and your high side pressure is 200-250 PSI, everything is happy. Now add 40º more ambient temperature and watch the pressure climb to 250-300 PSI. Next we'll add 1500-2000 RPM to the compressor and watch the pressure climb to 350-400 PSI and shut down the system. I've had it happen on my own vehicle (not the PW) and I've seen it happen on other cars. Drop the temperature 10-20º or lower the pressure and things starts working fine again.

When the high side is too high it's going to affect the low side PSI also. An efficient low pressure is 25-30 PSI and should give you 35-40º at the dash vent. But if the system is in the scenario I described above, the low side pressure will be too high also, and since pressure directly correlates to temperature in an A/C system, I can imagine you could see 50-70 PSI or more and up to 90º air temp at the vent.

I know DD spends a fair amount of time in AZ and I'm sure this isn't the first time his truck has seen triple digits. It might be something completely different causing the problem, I'm just saying it's a possibility and something to be aware of. The only way you could know for sure would be to recreate the conditions and have a set of gauges hooked up.

I've never had good luck reading air temp with a infrared thermometer. They work great reading surface temps, unless the surface is chrome or reflective, then it gets skewed. A cheap analog cooking thermometer seems to do a much better job in an A/C vent. It doesn't require any batteries and it's always on.

:patriot:

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Re: Strange A/C Problem

Post by Ducky's Dad » Fri Sep 07, 2018 1:37 pm

I used to use a cheap cooking thermometer but they are not "instant read" as are the infrareds. When I used the infrared on the trip I made sure the laser dot was always around the same spot on the back face of the plastic duct, behind the dash grill. So, I was mostly reading the temp of the plastic rather than the actual air temp flowing through the duct, but I made sure to hold the thermometer there until measured temps started to change direction. Even if readings were off by a few degrees, there is a lot of room between 17F and 94F when system is set to max cold.

Re high ambients, this truck has been in southern AZ every summer for the last 13 years and has seen temps substantially higher than what we had last weekend, but this is the first time the A/C has ever been an issue. Last weekend was actually fairly mild by Yuma standards.

Results of yesterday's shop time are that the A/C worked fine, including a 30-mile parts run by one of the shop guys who claimed it was freezing him out. Pressures checked out fine, refrigerant charge was fine, no codes on scanner, truck idled for a couple of hours with A/C blowing cold the whole time, all connectors tight and clean, no cycling of compressor, no interruptions in A/C fan operation. So, we decided to start swapping parts. Ordered a VDO A/C fan assembly because it's supposedly made in US and cheaper than factory part. Why a fan assembly? Because my cousin's son-in-law's '03 Dodge truck had similar symptoms and a new fan fixed his A/C. And a shop customer's Dodge caravan had similar symptoms and a new fan solved that one, too. How's that for scientific deduction and diagnosis? New fan is in, I'm heading back to Yuma in a few days, we'll see if it's fixed.

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Re: Strange A/C Problem

Post by Retired BLM Rig » Sat Sep 08, 2018 9:52 am

I found this chart in the FSM. My numbers that I posted earlier were a little off, but I was speaking from a general rule of thumb perspective. You can see in the chart how ambient temp affects pressure and vent temp (64º output is normal and acceptable on a 110º day). I don't know what the high pressure limit switch is set to, but if your fan quit working, it could definitely exceed the limit and shut off the compressor.

Keep us posted. :patriot:

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Re: Strange A/C Problem

Post by Ducky's Dad » Sat Sep 08, 2018 1:01 pm

but if your fan quit working, it could definitely exceed the limit and shut off the compressor.
Thanks.

That's what we suspect is happening, but hard to check the fan at 70mph. Fan works great sitting in the shop, so there may be something else going on. Swapping parts might only rule out the fan as the cause of the problem, but at least then I'll have a spare fan!

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Re: Strange A/C Problem

Post by DamageWagon » Sat Sep 08, 2018 3:15 pm

Referring to your engine cooling fan? Engine fan has almost no flow beyond the ram air flow once you get above 35-40mph. You could remove the fan and run highway speeds with no notable change.

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Re: Strange A/C Problem

Post by Ducky's Dad » Sat Sep 08, 2018 5:09 pm

Referring to your engine cooling fan?
Nope. On my '05 there is a separate electric A/C fan on the left side that is intended to draw ambient air through the little A/C radiator. Has is own motor and shroud, completely separate from the engine cooling fan. It is my understanding that the compressor will run only when the A/C fan is running, and we suspect that the fan may be quitting at high speeds and high engine loads, but have no idea why. We have heard that the A/C fan is a known problem on Dodges, so that's why I took a chance on replacing it.

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Re: Strange A/C Problem

Post by scoutpappa » Fri Sep 14, 2018 8:45 pm

Did the replacement fan fix it?

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Re: Strange A/C Problem

Post by Ducky's Dad » Sat Sep 15, 2018 9:36 am

Did the replacement fan fix it?
No. Just got back from Yuma last night and the A/C set a new temp record on the way home. Running up the long (20+ miles), gentle slope on Hwy 78 out of Westmoreland into the Anza Borrego desert at about 80mph, the A/C was set to max cold and highest blower speed. Had been driving for maybe 30 miles when I started the up slope and the A/C output was about 80F at the bottom, started climbing slowly right through 90F and finally hit 103.6F at the vents, measured with a new digital probe thermometer that I had calibrated against another new thermometer a few days ago. Got similar readings with my infrared. Outside air was 109F. When I got over the crest of the mountains (maybe 3000 feet), the A/C started to cool a bit and made 85F at the vents seem heavenly. When I got out toward Lake Henshaw on the slow downhill ride, the A/C vent temp got as low as 47F. When I left Yuma, A/C blew 85-90F through 75 miles of flat desert, with outside at 112F. Miserable drive. When I was a kid, we didn't have A/C and it didn't bother me. I must be getting old.

I have no idea what's going on with this thing. Mechanic tells me that the system reads multiple parameters through the ECU and something is obviously off kilter. There may be codes that the dealer scanner can find that his scanner does not show, so I may have to pay for a dealer diagnosis, and I'd bet serious money that they just tell me it doesn't work because I have done so much crap to the truck. Need to search for TSBs on the A/C, but quick search turned up nothing.

Forgot to mention that when I filled the gas tank, computer showed about 32 miles more range than normal for this trip, so that seems to confirm that the compressor was shutting down for part of the time. Mechanic has suggested wiring a temporary indicator light to the compressor so that I can see in the cab when it's running and when it's not. Seems like a good idea.

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Re: Strange A/C Problem

Post by scoutpappa » Sat Sep 15, 2018 5:18 pm

I'm no A/C expert but definitely sounds like something is wrong. On my 1500 2009 the compressor just died at 125K, no symptoms, but I keep an eye on any A/C issues that pop up in forums because I drive a black truck in Houston TX. For that one (the 2009) there was a reflash (recall) for the ECU for the blend doors (doors stuck in the floor only direction). Ultimately if you stick gauges in the system and the results for pressure meet the high and low side ranges I would look for another culprit like blend doors. Of course this sounds like it's happening at times when pulling over and slapping gauges on the ports is not convenient to say the least. Keep us updated and thanks.

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Re: Strange A/C Problem

Post by Ducky's Dad » Sat Sep 15, 2018 6:02 pm

Only happens at highway speeds or under heavy engine load (hills, passing, way over the speed limit, etc.). Coast downhill and it's cold. Drive around town at 35-45mph and it seems fine. Hit the freeway onramp and outlet temp goes up until you settle into a moderate cruising speed. Pass another car or go up a grade and it gets hot. Everything that we can check has been checked.

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Re: Strange A/C Problem

Post by Retired BLM Rig » Sun Sep 16, 2018 10:01 pm

If you want to continue your experiment of swapping parts, this is where I would go next. The sensor may be sending skewed data to the ECM.

From the FSM:

A/C Pressure Transducer

OPERATION
The A/C pressure transducer monitors the pressures in the high side of the refrigerant system through its connection
to a fitting on the A/C discharge line and its internal resistance changes in response to the pressures it monitors.
The powertrain control module (PCM) or the engine control module (ECM) (depending on engine application) provides
a five volt reference signal and a sensor ground to the A/C pressure transducer, then monitors the output
voltage of the transducer on a sensor return circuit to determine refrigerant pressure. The PCM/ECM is programmed
to respond to this and other sensor inputs by controlling the operation of the A/C compressor clutch and the radiator
cooling fan to help optimize A/C system periormance and to protect the system components from damage. The
PCM/ECM will disengage the A/C compressor clutch when high side pressure rises above 3172 kPa (460 psi) and
re-engage the clutch when high side pressure drops below 1999 kPa (290 psi). The A/C pressure transducer will
also disengage the A/C compressor clutch if the high side pressure drops below 193 kPa (28 psi) and will re-engage
the clutch when the high side pressure rises above 234 kPa (34 psi). If the refrigerant pressure rises above 1655
kPa (240 psi), the PCM will actuate the cooling fan. The A/C pressure transducer signal to the PCM/ECM also
prevents the A/C compressor clutch from engaging when ambient temperatures are below about 10º C (50º F) due
to the pressure/temperature relationship of the refrigerant.
A Schrader-type valve in the A/C discharge line fitting permits the A/C pressure transducer to be removed or
installed without disturbing the refrigerant in the A/C system.
The A/C pressure transducer is diagnosed using a scan tool (refer to 9 - Engine Electrical Diagnostics for more
information) .
The A/C pressure transducer cannot be adjusted or repaired and must be replaced if found inoperative or damaged.
REMOVAL
NOTE: It is not necessary to discharge the refrigerant system to replace the A/C pressure transducer.

FSM24-251.jpg
ACPT.JPG
A 2005 may have a different location, but mine is right above the compressor in the discharge line.

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Re: Strange A/C Problem

Post by Ducky's Dad » Sun Sep 16, 2018 10:36 pm

RetiredBLM, thanks much for that info. I hate just swapping parts, but we are stumped, so that might be a cheap way to eliminate one more variable. I'll get a parts price from the dealer when I get home in a few days. The replacement fan was almost $300 for the part.

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Re: Strange A/C Problem

Post by Retired BLM Rig » Sun Sep 16, 2018 10:48 pm

If you still have problems after that, the next component I would focus on is the fixed orifice tube that is built into the rear liquid line that runs between the condenser and the evaporator. If the orifice gets plugged, or in your case restricted, under extreme conditions it could cause the high side pressure to be too high and shutdown the system. The thing that usually causes an orifice tube to clog is compressor shrapnel, so if it goes that far I would replace the compressor as well and flush the lines and condenser (you may need to replace the condenser due to all the little nooks and crannies that would make it impossible to thoroughly flush).

Hopefully it's just the pressure transducer. :patriot:

Edit:

I just looked at my truck and there's an inline coupling behind the air cleaner box mounting bracket, that's where the orifice tube is. Sometimes the orifice tube can be pulled out of the metal line and serviced separately. If you could ID the type of material causing the blockage it might save you some money. Metal would be compressor shrapnel, black rubber could be inner hose lining coming apart and white plastic could be a ruptured desiccant bag in the accumulator.

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Re: Strange A/C Problem

Post by Ducky's Dad » Mon Sep 17, 2018 6:09 pm

Thanks. Do you run an A/C shop?

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Re: Strange A/C Problem

Post by Retired BLM Rig » Tue Sep 18, 2018 2:56 am

Ducky's Dad wrote:
Mon Sep 17, 2018 6:09 pm
Thanks. Do you run an A/C shop?
No, but I pretend like I do on the internet. :ugeek:

Seriously though, without having gauges and a quality scan tool connected at the time the problem is occurring so you can read live data, it comes down to guess work. The options I've tried to explain are the most logical to me. The last option would be the evaporator temperature sensor, if it senses that the evaporator is icing up, it will tell the computer to turn the compressor off. But I think it's going to be one of the other items.

I think your best bet at getting to the bottom of this is an A/C shop in Yuma. I wouldn't be able to reproduce the high ambient Arizona temperatures, that I believe are triggering this problem, here on the California coast. I would probably end up telling you that everything looks normal, based on the climate here. I also suspect that when the heat of summer passes, this issue will disappear until the next hot day.

Which brings up an interesting question... Have you ever had this problem occur at night when it's cooler, using the same driving scenarios?

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Re: Strange A/C Problem

Post by Bill2014 » Tue Sep 18, 2018 7:54 am

If there was a way to get a camera on the compressor clutch to confirm that it is really turning off under those conditions... It's hard to imagine that it's not, but confirmation would be great!
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Re: Strange A/C Problem

Post by Ducky's Dad » Tue Sep 18, 2018 10:07 am

Have you ever had this problem occur at night when it's cooler, using the same driving scenarios?
A/C works better when it's cooler, but I have had the problem at night when temps are high. Happened two weeks ago in Yuma, early morning, still dark so no radiant heat, ambients high 80s/low 90s, accelerating onto freeway ramp and then climbing grades. One of my new digital probe thermometers has a lighted display so that I can track that. Hard to duplicate at home, because I don't have the ambient temps, the long grades, or the ability to drive that fast without getting arrested.

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Re: Strange A/C Problem

Post by Ducky's Dad » Tue Sep 18, 2018 10:12 am

If there was a way to get a camera on the compressor clutch to confirm that it is really turning off under those conditions... It's hard to imagine that it's not, but confirmation would be great!
I don't have a GoPro and mechanic thinks the kids lost his, but we planned to do that a couple of weeks ago. Temporary test light on compressor may be the alternative. Can't get A/C to misbehave when truck is stopped, only happens under load and at road speeds. I'd really like to get this fixed now so that I don't have to deal with it when it gets hot again next summer.

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