AC Assistance Please, Only cool at speed.

[GCroyle]

TDR,



I admit to not knowing much about AC, so if I get a term wrong, just correct me please.



AC is not too bad at +55mph but when I come into town, hit some lights and slow down the temp rises noticably.



With a new gage, infrared thermometer and a vent thermometer, AC on, fan on high, no unusual noises, seems like correct air flow across vents and no differentation observed from drivers to center to pass side.



Air temp 80 deg, new gage on low side stable at 50-55 psi, the lines at the black can behind the battery hi side 107 deg, lo side 76 deg top of condenser 154 deg bottom of condenser 125-130 deg. Vent temp was 70 deg, condensation dripping from body, the line that I sometimes see almost frost on on some vehicles was cool to touch and had some condensation dripping, but not real strong, air was high humidity. I did not add any R134. Engine coolant temp has habitually been rock solid.



Your ideas please and thanks for your comments.



Gary

 

[E7mack96]

is the fan coming on at a stop... i mean the cooling fan at the radiator. . If not, this would cause loss of cooling at a stop due to a loss of airflow across the condenser.

It sounds like it may be low on R134a though with your temps. .

 

[rbattelle]

I had the same thoughts as Mack - if it's cooling well at 55+ then you likely have a fan problem. Fan should engage with A/C on pretty much at any speed below 20ish.

Ryan

 

[icman95]

If you determine that your fan is ok then-as Mack suggests- you might be low on r134a due to a leaking/bad/worn out evaporator core under the dashboard. I've had this replaced twice on my 2001 3500 and once on my wife's 99 Durango. The shop said that Dodges are notorious for having bad ones and they leak all the time. The one for my dually had a part revision 3 times. The shop said that tells them that Chrysler is trying to fix the problem, but may or may not have gotten it right yet. Unfortunately, getting at it requires removing much of the dashboard and is quite a project. Each time I had it done, it cost between $1000 and $1200. Ouch. If you need to have it done, then also consider replacing the heater core at the same time, as it is right next to it and would cost no more labor, just the part. That way, all the parts under the dash will be new and you avoid getting charged for labor to remove the dash a second time to do the heater core.



There are other reasons that the r134a might be leaking, but that's the only one that has happened to me so far.



Good luck.

 

[GCroyle]

Engine Cooling Fan

Thanks for the ideas.



The engine cooling fan is turning and sure looks to me like it is a viscous fan clutch system not electric.



Any diagnostic tips on the fan clutch system, this truck has never overheated or shown anything but a couple of degrees over normal. I just found a diagnostic test in a 1996 Dodge service manual that describes a test that includes blocking the air flow and temp readings etc.



On the way in today, overhead showed 77 deg, dash vent thermometer ran about 45 deg HIGH humidity, rear glass actually started to fog. Definite temp increase as soon as you slow down.

 

[rscurtis]

If your fan is working correctly, it should be noticeably noisy, even at idle with the AC on. The engine can idle for some time in traffic without needing the fan, so you wouldn't notice overheating if the fan is not up to speed. As a troubleshooting aid, place a fan in front of the condenser with the truck sitting still and see if that restores your AC while the truck is stationary. If it does, you found the problem.

 

[jtwcummins]

I had the same issues on my 97. Finally broke down and put an electric pusher fan on the front of the condenser. Used a relay and it picked up when a/c clutch engaged. Made a hugh difference in low speed cooling. There is one big stack of stuff in front of the engine, rad, air charge cooler and condenser and most of the fan clutches on the road in these trucks probably need to be replaced. One area that is done right is the engine cooling system, so if the fan cluth isn't working 100% you won't really notice increased coolant temp. When the truck is first started the fan should be VERY loud if the coupling is working

 

[GCroyle]

Guys, I think understanding and testing the viscous fan clutch function is a definite player in this situation, I need to investigate this fan clutch system.



The use of a test fan in front of the rad at home is doable, thanks.

 

[jelag]

Gary... .

My 04 and 05 both towing 20K lbs at temperatures into the 100's across the desert has not been a problem... I often pull into a rest area and let the truck idle and lock the doors and head to the rest room... . and come back to a cold truck... .

I've never thought about an extra fan... .

Our only problem has been the Grape Vine from Bakersfield to LA on I-5 in all the truck traffic... if we don't allow 100 ft between the front of our truck to the rear of a semi the larger truck will draft most of the air around the our truck... thus the area in front is a dead zone. . the engine will climb in temperature... as soon as we get the spacing we're fine... its like when you draft that close there's nothing moving and the fan can't pull air through... you can hear the fan start and never shut down for the 15 or 20 miles up that grade... .

I'd look at the tension on the belt and the fan hub... . I've read posts here about that.....
I know that Horton made some of these hubs and they have replacement for them. . perhaps their web sight might help... I also have a customer who is in Canada who is a Horton Distributor... I'm sure his guys might help... let me know if you need his number...

When you find the answer I'm sure we'd all like to know. .

 

[JCockerill]

vent temp should be 25-30 degrees colder than outside ambient temp once system has been runing. if slower speeds are causing your a/c to warm up signifigantly, sounds like not enough air flow through the condenser due to fan problem. either the a/c relay is not kicking on fan clutch or clutch is bad. they also sell an aftermatket electic fan that would add to the factory fan.

 

[GCroyle]

Jim,



If you're expecting me to come up with an AC fix, you have your money on the wrong pony! I'm game but it's outa my realm of comfort wherever that is.



Jcockeril,



Can you confirm about A/C relay kicking on the fan clutch? mine is an '05 and I looked this AM and it looks like a viscous clutch. I do know on my daughter's Concorde AC on = Fans on, you.



I'll look at the belt tonight.

 

[BGlidewell]

check the low side pressure. should be 35-40-45 PSI. I bet you are ~20ish.

 

[JCockerill]

sorry i didn't look at your year. if you have the fan clutch with aluminum fins on it check it and make sure it is activating when it gets hot. this style fan clutch has no relay. it is activated by ambient heat. these do go bad so check to make sure it is locking up when hot.

 

[Crunch]

My truck has had the rising temp at stoplights problem since I bought it new in '03. I thought I read about a TSB on it, but my warranty expired long ago and I haven't found the TSB info. I'm also interested if anyone finds the fix for this, especially if it's a cheap, or DIY fix.

 

[GCroyle]

JCockeril,



It's a spinning thing, I just dont know if it is at 50% of enging RPM or nearly 100% of engine speed, I need to do some tinkering, but most likely not until this weekend.



Rough day at the salt mine. I have a cold one that needs recycled in the fridge.



Back tomorrow.

 

[rbattelle]

Indeed the fan is a viscous clutch, with RPM feedback and control in the ECM.

The only test I know of for the fan clutch is to grab a blade and spin it. If the fan makes 5 rotations or more before coming to rest, the clutch is shot and must be replaced.

Mine will make a little more than one rotation, to give an idea what a properly functioning one does.

Ryan

 

[GCroyle]

BGlidewell,



I checked the low side yesterday with a new gage, saw 50-55 psi after it stabilized.



Ryan,



Sure wish I had another truck side by side to compare to.



Driving home tonight is was mid to upper 90's AC on outside air, 55-60 mph, yep all backroads for me to get home on, dash temp was about 60 deg, then I put it on RECIRC got down to almost 45 deg, big difference, ran it all the way home on RECIRC. When I pulled in the drive, I shut it off and quickly checked the resistance to rotate the fan, one finger to rotate with drag but I would not say that you could free spin it, nope. Couple hours later I setup a box fan in front of it and ran the AC, no big difference until I held it at 1800 RPM, things started to get cooler at the dash vent. Shut down and rechecked resistance at fan, still 1 finger w/o free rotation. It does not roar, IIRC it used (?) to roar or am I remembering wrong? I haven't noticed a difference in fan clutch resistance but I cannot spin it up to speed so hand turn test most likely is invalid.



Don't these viscous clutches use a bi-metallic strip that expands/contracts to control a valve in the unit that regulates operation and fluid involvement between spinning drive plates or something for lack of the correct term.



Took a quick look at National aftermarket suppliers for fan clutch, didn't find it yet.



Thanks.



Gary

 

[rbattelle]

Sounds like the fan clutch is working properly. At this point I think it's time to check the refrigerant charge.

At low speeds with the engine RPM between 1000 and 1500 there should be a pretty loud roar of air from that fan.

Ryan

 

[Bill Stockard]

Don't these viscous clutches use a bi-metallic strip that expands/contracts to control a valve in the unit that regulates operation and fluid involvement between spinning drive plates or something for lack of the correct term.

Gary

No, not on 3rd generation trucks. The operation of the fan is electrically controlled by the ECM (not by a bi-metallic strip) as Ryan stated. From the Factory Service Manual:



"The ECM controls the level of engagement of the electronically controlled fan clutch by monitoring the coolant temperature, intake air temperature, and A/C status. Based on cooling requirements, the ECM sends a signal to the viscous fan clutch to increase or decrease the fan speed. Fan speed is monitored by the ECM. Lack of fan speed will set a DTC. Fan speed and duty cycle can be monitored by the DRBIII. "





Bill

 

[tempforce]

the low side should be between 25-40 psi.

you noted that your low side is 50-55.

thats to high.

if you speed up the engine you may notice, the pressure drop.

if so, you may need more coolant.

to be sure, you need to know both the low and high side pressures.

if you check and the high side is low. you need coolant.

if both are high. your over charged or your condencer isn't cooling enough.