2nd Gen Non-Engine/Transmission Bonehead Air Conditioning Mistake?

[Matt42]

Over the weekend, I changed out my heater core that had a pinhole leak. It was a MESS, closely resembling oxide copper ore from the Globe district. The job wasn't all that bad, but a 30 inch broom handle was essential.



While I had the HVAC box out, I also replaced the air conditioner evaporator and the accumulator. The evaporator had the beginnings of corrosion on the base.



When I put it all back together, I followed the advice of the Dodge 1996 TSM and added 6 ounces of PAG oil to the system. I poured it into the accumulator. Then I reconnected everything with new O-rings and garter springs. I vacuumed out the system for about an hour, and managed to pull 28 inches of vacuum. Then I recharged with about 32 ounces of R-134.



Inlet and outlet pressures are OK, but the air temperature at the center vent will not get below 55F when it is 90F outside.



What did I do wrong? Did I use too much oil? Did I put it in the wrong place? Is my karma going away? The mixing door and cable work fine. I've done work on R-12 units, but this is my first foray into R-134.



Any advice will be appreciated!

 

[Gary - K7GLD]

*32 ounces?*



I that correct? sure sounds like a lot to me - but you surely musta checked before installing it...

 

[Matt42]

Yup

Originally posted by Gary - KJ6Q

*32 ounces?*



I that correct? sure sounds like a lot to me - but you surely musta checked before installing it...

Seemed a little high to me, as well. But it's on page 14-16. "The R-134a system charge capacity is 0. 9 kg (32 ozs. ). " Cooling improved, to a point, as I added R-134a.



I recall having to use 36 ounces of R-12 in a Jeep.

 

[lil red cummins]

if you have air conditioning gauges, put them on. if you don't, you really need them. i am assuming this was a conversion from the old R-12.



i have done over a dozen conversions and never had a failure, but i always buy the conversion kit that has the oil prepackaged with the 134a charge and the quick disconnect adapters for 134a gauges. most likely what you did should be alright.



the pressures should run exactly the same as when it had r-12.

generally you will use LESS 134a than what was recommended for R-12. i dont remember what the percentage is, but i am thinking it is between 10 and 25% less. the gauges tell you how much to put in.



what i recommend is put the blower on low and make sure the low (suction) side will come down low enough to make the compressor cycle off. this is typically between 24 and 28 psi but not absolute. you may have to raise the rpm's to make this happen. don't go over 2000.



if this works out ok, then switch the blower to high and raise the RPM's to around 2000. (get a helper) and hold it there. the high side should increase to at least 200 psi. the ultimate pressure is relative to outside temperature, compressor efficiency, humidity and blower efficiency, your fan clutch and a whole bunch of other factors. it could go as high as 400 psi on a 95 degree day. if it gets that high, bring the engine back to idle and shut the system off. you may have an overcharge or other problem or it might be OK. its just dangerous to play with it at that point. the pressure reliefs can start blowing off at between 450 and 500 psi.



hopefully the low side should not go above 40 to 50 psi. if it does, it still doesn't mean there is a problem. try lowering the blower speed and see if the low pressure drops.



as far as outlet air temp goes, check it with the blower on low. you will get the coldest air that way. you should be able to get the air temp down to around 45 with a temp probe in the duct.



this is by no way a complete or thorough explanation, but should give you somewhere to start.



this is a lot easier for me to do than explain. good luck.



jim

 

[stacerbob]

Cummins fan doesn't pull much air at idle. Try a fan in front to simulate driving speed. Just a little too much or too little 134 will hinder perfermance. 55 @ 90 ambiant temp! it can only do so much

 

[Matt42]

A little more background might help. The truck originally had R-134a.



While I had the HVAC box out, I decided to also replace the evaporator and accumulator, since they had to be disconnected and discharged anyway. I replaced the accumulator with an Air Pro 49004, and the evaporator with an Air Pro 58005. As directed by the Dodge TSM, I replaced 6 ounces of PAG oil by pouring it into the accumulator. Dodge recommends 2 ounces for the evaporator and 4 ounces for the accumulator. (I think I used PAG 100. ) I reconnected everything with new O-rings and garter springs, and evacuated with a Mastercool 1. 5 vacuum pump for about an hour.



Low side pressure is about 40 - 50, high side is about 250 - 260 at an ambient 90F. This using a set of cheap gauges.



At about 90F outside, the very best cool air temperature I can get is 50F. Sitting at idle, the temperature will mostly be 60F. Temperature on the freeway at 60 mph will be about 52F. It was MUCH cooler before this exercise.

 

[bighammer]

First of all, I know nothing about A/C. It sounds like 50 to 60* output would be comfy when it's 90* outside. (unless you want your glove box to be cooler/ice maker)

 

[Matt42]

Well, not exactly comfy ...

Originally posted by bighammer

First of all, I know nothing about A/C. It sounds like 50 to 60* output would be comfy when it's 90* outside. (unless you want your glove box to be cooler/ice maker)

If the 50 to 60 degree output would cool the interior of the truck to 70 or so, it would be fine. The heat gain from outside due to dark paint and greenhouse effect from the windows will raise the interior cab temperature to 120F or more on a 90F day. 50 to 60 degree output air (at the vent) gets overwhelmed pretty fast.



We learn not to carry chocolate bars, or even soap bars, in the glove box.

 

[Bob4x4]

To run the performance test,set idle at 1000rpm. If the clutch cycles bypass the cycling switch. At 90 degrees ambient you should see 37-45/200-240 psi and should blow at 37-48 degrees at the center outlet,high blower and on max a/c. 2 lbs of 134 is correct for all years BR and BE trucks. The fan clutch will have to be engaging to keep the high side pressures in line.



Bob

 

[Dan_69GTX]

Hi Matt.



I do a lot of work on A/C and finally decided to work on my truck (also a 96). Isn't it the mechanics vehicles that always are neglected?



Anyhow - Here is what my problem was and what I found out. I had vent temps in the mid 50's, yet pressures were ok but a little high (44 on low - 250 high). I thought there was air in the system - I used a refrigerant identifier and - no air - pure 134a. So, I sucked all the 134a out, and refilled - exactly 32 oz - same problem, so I slowly removed some - a total of 4 oz - and have much better results - cooler vent temps - mid 40's and better pressures.



All this to say - I found the 2lb recommended amount to be too much for my system - a good working system - no moisture, air, not overcharged with oil, etc.



I'd recommend you remove 3-4 oz of 134a and see how it works - probably much better.



Remember, r-134a is MUCH pickier about amount of charge than r-12 was. This applies to vent temps, pressures, and oil flow. So, when you are running a little low on r-134a, you are also losing a lot of lube to your compressor. Which is why for "speed" most shops will always suck out the r-134 that is in there and recharge with the recommended amount and be done with it. That makes them less liable for problems, and then the "parts replacer" doesn't have to learn to read gauges, while monitoring vent and line temps.



Diagnosing over the internet can be tough - so make sure you have checked the rest of the system for problems - such as condensor temps, inlet/outlet of evap temps, etc.



Any other questions - please post or pm me.



Thanks!

Dan

 

[Dan_69GTX]

Oh yea one more thing

Yes, it sounds like you did everything correct. Do you have any idea what the pressures were before you took the system apart? Any idea how much 134a you took out of the system?



I see you are from Glendale - Used to live there - left in the early 90's - had a place close to 63rd ave - just south of Bell.



Dan

 

[rattlnrench]

Make sure that the recirculation door is opening allowing the system to cool inside air. You should be able to hear the difference when the door opens (A/C Max). You'll never get really cold air out of it on a hot day without it working properly. It's possible the vacuum line was not reconnected on assembly.

 

[Matt42]

Vacuum lines are OK. Recirc door opens & closes with its usual muted whoosh and change in air flow. I bypassed the heater core last night to see if the blend door in the HVAC housing was stuck. Today in 85* weather, the center vent output temperature was the same whether set on heat or A/C. Based on the diagram of how the blend door works, and how it looked while I had it apart, I don't think the blend door is the problem.



I'll be removing A/C components this weekend, draining the oil from each, and measuring the volume. My alternative is to take it to the shop and have them do the same thing. The shop said that's what they'd do, and I could do it just as well.



Evidently, relying on the "book" numbner for oil to add was a bad idea. The book, I'm told, is always wrong. Oil has to be drained and measured. R12 systems were much more forgiving.



Sigh.

 

[Mackie007]

Matt,



I'm your neighbor down here Tucson and do a fair amout of AC work. As mentioned above you are a bit over charged, this was a result of adding too much oil (only an ounce or two) combined with the fact that here in desert AC systems perform better by setting the charge 5% to 10% under the factory specs.



That being said rather than doing a full system flush and replacing the acumulator to get the oil charge correct. Just recover the system and set your new charge at 27oz (5oz under specs) then check your guages and performance. You could then add an ounce or two of freon if needed. This should get your truck within acceptable parameters, even with the slight oil overcharge.



Best of luck,



Mac

 

[Chris N5CWM]

I've been messing with warm output air on my 2001.

The discharge temp is about 8F cooler than the outside air; today it was 68F out and my temp probe was showing 60 from the center vent on the dash.

The gauges (decent dual gauge setup with manifold) show 42 on the low side and about 125 on the high side. I have a RAYTEK infrared temp gun and was able to get 42F on the line going to the evaporator near the orifice (by the airbox). So why is my output air only 60 F on a 68F day?

Is my high side pressure too low? The earlier posts mention 250 but that is at 90F or so ambient.

I guess I'm gonna check my diverter door and see if it's the cause.



If any of the above numbers sound out of whack or I need to give more info, which I can, please adivse... anyone. Thanks!

 

[Chris N5CWM]

I checked the system mechanically. Good vaccuum. All of the doors and actuators are moving full travel. Evaporator is not dirty. The high side pressure is low so I'm going to bring it up to ambient temp multiplied by 2. 4 so if it's 75 outside, I'll add freon until the high side is 180 PSI. It was about 125 today. Still only cooling the incoming air 8F less than outside air. Gotta be low on freon.



(Feel like I'm typing to myself here).

 

[Dan_69GTX]

Is the compressor cycling a lot?



Any idea if there is air or pure 134a in the system?



Having 43 lb at the low and 120 at the high doesn't sound right for low freon. You should have a low number on both if you were low and the compressor should cycle a lot.



It sounds like it could be more than one problem - such as low charge with a restriction.



Air is a noncompressible and will do strange things with the pressures



Dan.

 

[Chris N5CWM]

Hooked up the gauges again and put in 11. 5 oz of 134a. Air coming from the vents is now 42F. Ambient 84F, so I added freon until the high side was about 195 and let it stabilize. At 2,000 RPM the low side is 44 and the high is now about 199.



Yes the compressor was cycling a lot. On about 8 seconds, off about 6 seconds at first. The system has never been apart. Truck has 58K miles on it, and I am the original owner.



Now to keep tabs on the loss. There obviously is a leak somewhere. We'll see how long this lasts then I'll have to get a UV leak tester. Hopefully it's not a fast leak.

 

[Dan_69GTX]

Glad to hear you got it working!



Just remember - Wal-Mart, pep, boys, etc all sell r-134a with a stop leak.



DO NOT USE THESE - except as a last resort - before you sell the vehicle or scrap it.



Reason - All A/C equipment manufactures (to fix a/c systems)will VOID the warranty if sealer is found in the machine. I ALWAYS test for sealer before I work on a car. If it has a sealer in it - I normally will refuse to work on it. If they REALLY want me to - I will - but there is $120 just to remove the old stuff, then they get to pay for new hoses, compressor, condensor, evaporator, etc, etc - you can not flush the stuff out. Let's just say this cost is a "little" greater than what it would have cost to fix the thing right in the first place.



FYI - There are 2 types of sealers - one swells o-rings (and internal seals of the a/c machine) - the other hardens in contact with moisture or air - plugging lines, etc, etc.



Dan

 

[I-6DZL]

Matt - and everyone else



I also own a 96, 134a from the factory. truck was totalled, put in a new condensor and accumulator. On the 134a service sticker on the radiator core support my truck says 1. 75 lb of 134a. Check your sticker and plz let me know, i'm now very interrested. My a/c blows 39 to 41 out the center with it on the 3rd fan setting (i've found the highest fan setting is just too darn fast to get the most accurate reading) I would try what others have been saying, take some of the charge back out and try again.

Keep us posted, good luck



curtis