AC Assistance Please, Only cool at speed.

[GCroyle]

tempforce and Bill,



This is getting interesting. I would think with our electronics that it should be controlled by the ECM, I just haven't seen the actual cable connection, it must be coming in from the front of the fan.



I have a small bug collection but the truck is not used off road, so I'd be super suprized if somethng was clogged up, but stranger things have happened.



When I put the box fan in front of the condensor but before I turned t on, the fan was already turning from the air flow from the engine fan.



I just bought a new DIY'er gage and filler system, but w/o training, I didn't get the full gage set, can't test hi side yet. I do have a scan tool can check for codes, but it just reads and erases at best.



When I recorded the low side reading earlier, truck was at temp, engine at idle.



More to learn, thanks.

 

[icman95]

If you decide that a leak might be the problem rather than a fan issue, then you might want to put a dye in the system to help find the leak. It is usually a neon green color that is put in the same way you put in a recharge of r134a. After it's in, you run the system to circulate it and then visually inspect all parts of the system to see where the neon green color is leaking out. The only catch is that sometimes you can't see every part of the system under the dashboard without taking the dash out.

 

[tempforce]

please do not use a leak sealer. it hardens when exposed to air. good to fix a small leak. but very bad if the system is ever opened. all of the components will need replaced after being opened. yes some items may be cleaned. but the stuff will cost you big $$$$ if used.
i'm still thinking it's low in charge. but personally would not add coolant until i knew what the high side is.
currently i'm waiting for connector adapters, so i can check my truck. as it's not cooling like it did last year.
if it needs coolant, i plan on switching to dura-cool. it's a non global warming or ozone depleting unlike r-12 or 134a.
takes less coolant with more system cooling.
also doesn't require a license to use.
if you have any r-12 or 134a in your system you still need a shop remove it and place a vacuum on the system to check for leaks. then take it home and fill myself.
in your situation a full gauge set is the only way to be sure you have the correct amount of coolant. or that the orifice isn't partially clogged.

 

[GCroyle]

tempforce, iceman95



Thanks for the ideas and "cautions" I do not intend to do more harm than good. If I can find some air flow issue, I can probably take care of that. I have fixed a couple with a top off, or did I just get lucky, I did use a low gage of course, don't have a full set.



If I don't find a reasonable solution, it will go in to the team that used to be my small town Dodge dealer until they got the rug pulled out from under them.



I think I felt a cable at the bottom of the fan clutch, but I'll get under it tomorrow to poke around a bit more. I want to try the cycling of the AC and compare to fan volume, if it is controlled via ECM, should be able to tell when it kicks in easily. Need another truck for a side by side.

 

[jelag]

Gary... .

Understand that if the belt slipped on the compressor it wouldn't come down to temperature at low speeds but there might be enough belt tension on the fan to prevent overheating at idle... . and a undercharge condition might give you the same result... .

At speed, you have more engine speed to push the compressor around with a loose belt, thus it cools...

Also a loose belt would show higher than normal low side pressure as the compressor is not caught up... .

I'm guessing that there is a torque rating for the tension... ...

Also your box fan in front sort of moves towards my point... the compressor is not cycling enough R134A and that's why the box fan doesn't work... loose belt, not enough R134A...

 

[E7mack96]

i still think it is the fan... mine did the same stuff... and i added a pusher fan. The factory fan should roar with the ac on, even at an idle... if you got a thermal gun... let it idle for about 5 min with the AC on... then shoot the temps at the condensor... is it really hot?? or just warm... discharge from the compressor would be really friggin hot... and return side should be ambient if enough airflow. another thing mine did, (i have a AC cert and guages) was that the discharge pressure would get to 400-500 psi and kick out the compressor via the high pressure safety switch. then once pressures returned to close to normal, it would cycle on again. this made low speed cooling very poor.

Tony

 

[GCroyle]

Jim,



I heard you weren't busy this weekend, grab your gage set, get on the Wing and I'll have breakfast your way when you get here tomorrow at 8AM OK?



First b-fast and BS, then fix truck, tour Sandhills, backyard campfire, heck, I'll let you bunk in the Silver Bullet then you can head back to Spokane in time to open up monday, OK! Sounds like a plan.



Alright, incase you are tied to the house, honeydo's and stuff, I'll check the belt. I'd be irked if you were right, but I'll get over it.



Take care Jim and thanks.

 

[GCroyle]

Tony,



I do have a thermal gun and I saw 154 deg at the top of the condensor and about 130 at the bottom, but I would not say that the fan roars, I'm going to observe the fan at idle with AC off and then cycle it and watch and feel the difference, that is after I do Jim's belt check and clean up from fixin him b-fast. I tried it a lunch today, not much difference but I need to check it a bit closer.



Thanks,



Gary

 

[GCroyle]

Update,



We have an '07 at work and I fired it up and tried to feel the fan breeze with AC on. I could hear it ramp up and feel an increase in airflow. A reference point.



I did find the fan clutch cable, unplugged it, darn thing has 5 wires in it, all light gage, that's nice, plugged it back in.



My truck today will cool down at speed and in particular with recirc on, about 90 deg and hi humidity.



At home tonight I checked for fan ramp up and by george, it felt a lot like our '07. You can notice it step up.



I ran my truck in the driveway and here is where it gets a bit iffy. The low pressure gage would drop to 35-40 and you could feel the tubing get cool and seemed good. Then it would go up to 50 and stay, the tubing getting warmer. I just let it idle and it sat at 50, not good inside the cab. I have not noticed the compressor cycling during this test, it just runs.



Next effort rig the gage so I could see it from the cab, rev it up to 2000 and the pressure drops to 35-40 and you start to feel cooling kicking in, let it idle and back to warmish air.



I don't have a high pressure gage, but so far this post seems closest to the target description and problem.

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.

tempforce, I'm assuming that coolant is R134, I haven't seen any air flow issues. Any chance you could review and comment please?



I have not added any R134.

 

[Prairie Dog]

I remember early on in the new third gens there were trucks where the wire for the fan wasn't secured well and it would end of getting clipped by the fan. You can check the wire by laying under the truck and looking up the back of the radiator.

 

[GCroyle]

Prarie Dog,



I'll check again, but the first time I looked all looked OK, wire in guide tube seemed in place.



I think it's time to get a high pressure gage on it, too many questions unanswered.



Thanks.

 

[tempforce]

sorry i've been off line for a while. i hope your cooling now. but your low side pressures indicate that you compressor isn't putting out enough volume. to lower the pressure on the low side. a good sign that your low on coolant.

 

[GCroyle]

Update.



I finally took it in to the team that was my local Dodge dealer until they got axed for being in a small market. I trust them.



They checked pressures, fan actuation including controlled actuation with the fancy black box thing and test drives. Pressure all checked OK, fan OK test drive, they agree with me, pretty good at 55+ noticeable temp increase at stop and go.



No repairs made and nothing solid confirmed.



I ran our '07 and at idle it runs noticeable cooler in the AC, the correct tube gets COLD and the other tube gets HOT etc, heat is being exchanged.



Mine will just stay "unfunctioning" (poor word choice I know, but this ain't a clutch) under the same conditions.



I plan to put a 3' warehouse floor fan in front of the engine and at idle, give it one more try. If that 3' fan doesn't change anything, then the only part that I am hearing from my shop is that the orifice tube might be restricting the flow. This system has neve been opened since built.



What say you TDR, how do you diagnosis a restricted orifice tube? I searched it here last night and didn't see a lot of threads.



FWIW, I topped of our '97 last night, slow leak, truck is getting older, hit it just right, works stable, one line good and cold, one line hot and this is with the old viscous thermal strip fan.

 

[icman95]

I'm not a big fan of the theory that things don't work right "just because". The shop is guessing that it is a restricted tube but if not, then it has to be SOMETHING. No such thing as working yesterday but not today without a good reason. Did they put a dye in the system to check for leaks? Even really slow leaks should show up with this. Otherwise, another shop for a second opinion? I was just catching up on a backissue of the mag and was reading about clogged condenser with dirt/oil/bugs. Don't remember if you said you checked for that and too difficult to look back on this phone I'm typing on. Possibility?

 

[GCroyle]

Ken,



I can't rule anything out, this is a bit out of my comfort zone. No, I do not think they added dye to check for leaks, I checked on ALLDATA today at work and they have a touch here then touch here procedure, using just your hands to feel the temp on the lines, really no tools req'd to check the orifice function. I'll do it tomorrow.



I have a city grade bug collection and almost ZERO off road time, so it looks real clean to me, need to use a light and look for obstructions.



I also should clear one thing up, IIRC I had this truck in shortly after I bought it and asked to have the AC checked, nothing found ..... forward several years. This truck has not been a Cummins Powered ice box, but I let a friend drive it about 25 miles or so and upon return, he remarked about YOU NEED TO GET THAT AC CHECKED! based on comparing to his '07 that started the process along with the hi temps and hi humidity that SC has been in, really taxing on staying cool.

 

[E7mack96]

i can tell you that it could be restricted some. its possible that the dessicadent is breaking loose and partially obstructing the orifice tube. I had this happen to my 2001 dodge durango. it took them like 5 trips to figure it out. on a more personal note, I worked on the big orange trucks for about 2 years, as their a/c guy. I replaced maybe 5 of the orifice tube blocks in the whole time I worked there. Most of those were clogged due to oil puddling in the sleepers' lines. only 1 or 2 in the cab side of the system. and those were both due to the dryers being installed backwards by a doo-fus at another shop. (yep they would bolt up either way)

 

[GCroyle]

We have been in a hot and extra humid streak. Latest on my AC woes.



I no longer suspect the fan clutch.

I have not seen any clogging of airflow, but I have not dis-assembeled anything.

Nothing makes me suspect the belt, everything else seems powered up just fine, no problems.

Positive note. I drove it in 5th at about 55mph and the center duct air temp dropped to near 40 deg on recirc. ambient was low 90's at the time. Truck ran for about 30 minutes prior to 5th gear run.



Why does it work at high RPM but drops markedly at low RPM?



I discussed with an old friend of mine who was a Field Trainer for Chrysler up until a couple of years ago. He had a couple of thoughts, one is related to low compressor RPM and the other is the sensitivity of the R134 charge weight, over or under by just a bit and performance drops. He discounted the possible clogged orifice tube in this situation.



One suggestion was to take it to a shop that has the (name unknown) machine that removes the charge, weighs it precisely and recharges it with the factory spec amount of R134.



I know this ain't easy, thanks.

 

[E7mack96]

well as a worst case scenerio, the compressor internal valves could be wore out. I see this a lot in reefer compressors , not so much in car ac compressors.

 

[HHhuntitall]

Don't overlook the simple wash of the condensor. I didn't see that suggestion in the threads, but I may have overlooked it. I work on a lot of older trucks, and many, many times, excessive head pressure on the compressor, and lack of suction on the low side is evidence of a faulty compressor or a dirty condensor. If it can't cool the freon, it can't cool the truck. Washing with a good soap or engine degreaser will do wonders, also for the engine cooling system. If it can't pull enough air across the fins to cool the freon, it can't do what it's intended to do. This also will cause your engine fan to run excessively... . Weight charge may be a consideration as well, if you've lost too much, but without it cooling freon at the condensor, it's will be difficult to diagnose, and won't work with the proper charge, either. Just my suggestion.

 

[RVTRKN]

You need to check all pressures and sub cooled temp and super heat to diagnose it as well as delta T from the blower. Basic AC rules apply.

low high pressure/ high low pressure = low capacity compressor

High high pressure/ normal low pressure = non condensables (air) in system.

low high pressure/ low low pressure = low on refrigerant





Sorry, have the wife in my ear to go to family function, will publish full list when I can. Point is you need all information to diagnose it.