A/C Help -- Charge Question
 

1980 300SD: Had bad freon leak. Still using R-12. Replaced high and low hoses, seals, o-rings, receiver/dryer, have begged, borrowed, and stolen four 12-ounce cans of R-12, and two 4-ounce cans of oil charge, and now ready to pull a vacuum and recharge. How much oil? How much freon? What should high and low pressure readings be at 1500 rpm engine speed? A/C outlet temp?

Temps in northeast Arkansas in low nineties with humidity near that, too. Really miserable, and only want to do this once. Any help will be appreciated.

Hopefully Larry Bible can help you with the rest, but my book shows: Oil Amount for 1978 -1980 300SD = 5.8oz, Refrigerant 2.66lbs, Low Pressure 22, High 205 (@80deg. ambient temp.) This data is from a Haynes Automotive Heating and A/C Book. Hopefully you have manifold gauges because anything short of using them is winging it and unsafe in my opinion...PM Larry Bible and cross your fingers that he has time to help.

If you flushed the condensor and evaporator you would need 6-8 oz. I have read in places they (116) takes 8 and other info says 6.

Having too much oil will hurt cooling.

I added 6 to mine after doing a compete flush and rebuild in April.

My red factory a/c info tag in front of the radiator says 2.2 lbs of R-12.

I can get around 42 degree vent temps so far. I was a little low and added some today so we will see if vent temps improve any.

After clearing up the site glass, my low pressure was 25 and high was about 200. They held real steady after the condensor fan kicked in. This is at 1000 rpm.

Good luck and a cold A/c is REAL NICE!

Thanks, J.D.; That Helps
 

I hope to get this thing up and running on Tuesday, and will use your figures. By the way, I knew a J.D. Blann, from Nettleton I think, at ASU in the mid-60's. That you?

My '79 SD has been converted to r-134a. If I flushed it and then pulled a good vacuum on it, could I improve my cooling very much to make it worthwhile? What parts would have to be replaced?
Thanks
David

there is always oil in the system. (unless you flushed)
usually we replace 1 oz for each hose and 2 ozs for rec/drier.
in your case this totals to 4 ozs.

The A/C in my car really stinks. Not literally. If it is 85 outside, you need to have the vents blowing directly at you to be able to keep the windows up, and that's moving down the road. You get restless sitting at a light, and this is after being topped off and it's still holding.
Thanks
David

check pressures

check the evap temp..

too much refrigerant can cause this..
Run 134 a little lower than specified...

check for air breach in evap box

David,

If you want to simply perform an evacuate/recharge on your 300SD, I would suggest at least replacing the receiver/drier and switches, of course since you will be emptying the system you might consider going ahead with a new expansion valve as well. Anyhow, if your car has 134a in it, you will only recharge the system with 80% of the original R-12 capacity. By a rule of thumb, 2 ounces of oil should be added anytime a recharge is done but it really depends on how much you recover from your car's A/C system on the recovery cycle with the machine. I would set the vacuum to run for at least 1/2 hour and make sure it holds at least 30 in/Hg for no less than 10 minutes AFTER the vacuum operation is complete. Add the oil while system is under vacuum and then begin charge operation. As for which oil to use, we have had excellent results with Castrol PAG 46 which is a synthetic compressor oil and already has UV tracer dye in it. Roughly $8 for an 8 ounce bottle.

My low pressure is at 35 idle and about 27 at 2500 rpms. I knew about the 80% thing, but we weren't sure exactly how much was in there to begin with. What do you guys think of my readings? Should I convert back?
Thanks
David

How can I check the evaporator temp? My r/d is original, or it appears to be. It has all the paint flaking off and the sight glass is dark yellow and nothing can be seen inside of it.
Thanks
David

Abner,

Not me. I have always lived in south Arkansas. Went to school at SAU Magnolia.

Back to 116 Mecedes:

WANT '71 280SEL,

I did the recirulate mod on both my 116 cars to have 100% recirulate only when the compressor is on. This should help some.
I didn't do a before and after so I can't say exactly how much it helps.

Here is what you do:

Remove the rh lower panel then the air duct. Look for a pink vacuum pod. It will be the outer most pot next the kick panel.

Remove the vacuum line and plug it. This will keep that pod from keeping the flap open to 20% fresh.

WANT '71 280SEL,

I use a meat thermometer I got at a truck stop to check vent temps. Look in a Pilot or Loves in the trucker parts shelves. They are a few bucks and work great. It has a clip like on a ball point pen and a small dial that indicated the temp. Really helps to determine what you AC is doing.

I can't help much on the pressures for 134a. The original dryers may not work as well wth 134a. If it is indeed an "original" R-12 type.

Good Luck to all!:D

So the air my car is cooling is 20% fresh, as in the ouside air. Then the remaining 80% is air in the cabin that is re-cooled? I'd like to have something like newer cars with recirc. The pod line that is being closed, what does it control? Howe does it recirculate air only when the compressor is on?
Thanks
David

A lot of references and material has already been posted on this forum... a search can really be helpful....

for instance:

http://www.peachparts.com/shopforum/showthread.php?threadid=72821&highlight=thermometer+pocket

The pod that I unhooked on my two 116 cars only purpose as far as I can tell is to keep one fresh/recirculate flap open so 20% outside or fresh air is coming in. So when the compressor is on it would hold the flap open.

This flap would stay open all the way and when the compressor switch is turned off when turned on it would close up but not all the way. Unhook the line and the flap would close al the way. Plug the line with somthing.

If you look you can tell exactly what and how to do this on you own car. It was a painless and easy mod.

I have read here about doing the same thing in a 123 car but I have yet to sort it out in my project 123 car.

Happy to help.

Do you find your w116 A/C to be more than acceptable?
Thanks
David

sight glass is dark yellow; due to contamination
 

Hello David

Legal Disclaimer:
Only a trained licensed mechanic should service the air conditioning system, in plain English, do not mess with what you do not understand, it can hurt or kill you!!!!!
If you use anything written herein, you assume full responsibility.
This is a For Your Information technical paper, with opinions and personal preferences expressed, NOT a DIY.

How I do my cars FYI.
The receiver dryer sight glass is dark yellow; due to contamination and plugging of the R12 receiver dryer.
Replace it with a R134A dryer and pull vacuum on the system for six hours.
I demand no vacuum loss for one hour on my cars, or I reseal the whole system.
Add four ounces of PAG oil and charge with two pounds of R134A.
A digital thermometer will be needed.
The next pound of R134A may take an hour to get just the right amount in the system.
You add R134A until the low side reaches fifteen psi; then add a two second shot to the low side, wait for it to stabilize and repeat as needed.
Warning, do NOT exceed factory high side maximum pressure specification.
I have seen properly cooling; converted R12 too R134A systems, with low side 22 - 32 psi, and high side 180 - 245 psi.
This is engineering and art.
The better the system is sealed; the better it will function, if charged correctly.
In climate control laboratories; you must start every system setup with a charge determination.
A proper charge determination requires a million dollar test chamber; and can take 72 hours at $400.00 per hour.
The final determination of weather the system is charged is subjective.
Is it cold enough for you????????????
A vent temperature of 34 F – 35 F is acceptable for my cars.
I prefer to put thermistors on the evaporator core and keep tweaking the charge; until it hits 33 F, but that takes a lot of time, and I do blow old lines some times...........

WHunter, You don't FLUSH ?

I thought it was dark yellow becasue it's 25 years old. I'll look into a new one and talk to my mom's cousin to see if he'll hook up a vacuum pump to it. Will the vacuum pump take out all the oil? He thought that it would still have some oil in the compressor after a vacuum pull. He probably wasn't thinking 10 hours though.
Thanks
David

Hmmm
 

As stated; this is on my personal vehicles.
If I am resealing the total system, yes.
If I am replacing a bad compressor, yes.
If all components are off the vehicle, yes.

Generally, conversion from R12 to R134A is not an issue.
I accept a systen capacity loss of roughly 2% on a good system.
Converting back to R12 is not as easy, flushing is needed, all seals and O rings must be replaced before proceeding.

OK,, from your own setup in your example :

"The receiver dryer sight glass is dark yellow; due to contamination and plugging of the R12 receiver dryer."

For anyone else this would definitely suggest that a full flush was in order... It means that something ( perhaps the dessicant bag in the R/D gave way, etc ).... bad is in the system... and flushing is the only way to get it out and start with a good chance for longivity from whatever is done to it...

In other words , your example was not a simple " change from R12 to 134 in a good looking system".....

I just want others to be aware of the need to research and make good decisions with regards to cleanlyness... since LarryBible is less available these days.... LOL

Damn, the more I read about what this is going to take the more futile it seems.................................

I want to go through this soon myself as I am real unhappy with the R-134 conversion that was on the car when I bought it.

And the more I read the more confused I get. I know my stuff on the mechanical end, but I am lost with the A/C.

Whuh Oooh
Something is wrong here!

R12 is fine with the old fashioned "O" rings. R134 has to have those green thingies. Changing from R12 to 134 requires replacing the "O" rings, going back to R12 does not. R12 is fine with either type of "O" rings.

R12 is normally used with mineral oil. All the oil has to be removed and replaced with synthetic when changing to 134. The synthetic Ester does not mix with mineral oil.

I think the preasure is sopposed to be 25 lbs on the low side and 2.2 times the ambient temperature on the high side. You're going to have to look that up.

Pull a 29 inch mecury vaccum and hold it for five hours. If it does not hold, restart vacuum pump and pump back down and maintain for at least 2 hours. The system must bew able to sustain 29 inches without a pump for at least 2 hours. If not there is a leak or fluid left in the system boiling.

The A/C thermometer is about $5.00 at harbor freight.

Remember once you have converted to 134, you have a 134 system. It is not legal to convert a 134 system to R12.

The tag that came with my compressor said 6 to 8 ounces of oil. Another source said 6.8 ounces. Take a two ounce syringe and add 2 ounces to the compressor. Then put the rest in the evaporator, drier, condensor, and hoses. Some sources say 2 ounces in the condenser, some say spread the rest around equally. So 2 ounces in the compressor, 2 ounces in the condenser, an ounce in the dryer, an ounce in the evaporator at the expansion valve, and an ounce in the hoses should be OK.

Always wet the "O" rings with the oil you are going to use before installing.

Legal or not............its a 1979 in my case. I want it working as it was intended to work. And if thats with R-12 then so be it. As long as it won't cost me an arm and a leg.

I do not see anything wrong with making a 1979 vehicle which came with R12 back into an R12 vehicle when it is discovered that it won't function properly with the R134a.

"systen capacity loss of roughly 2% "
I am sure you meant 20 percent.... right ?

Variables... confusing
 

Aaron mentioned pulling 30 inches of mercury ...
another mentioned 29 inches....

These are not absolute figures ..... the amount which one can pull depends on several things.... mostly barometric pressure..... but if you are in Denver or Switzerland on a mountain peak you will never see 29 inches...

Standard barometric pressure is defined as 29.92 inches of mercury at sea level at a certain temperature... don't remember but would guess 72 F....

I just did not want anyone fretting when doing this that their guages were not showing the " right" numbers....

I am really glad several people have mentioned keeping the vacuum running for HOURS..... five , six, etc.... THIS is VERY IMPORTANT.... because you are trying to boil out every last molecule of water which you are able...

Old mechanics with the old style vacuums used to regularly set the machine up and leave it OVERNIGHT....

More is better in other words.... you can't get TOO much water out... and you can easily shortchange yourself and leave big problems inside your system...

The EPA goal of course is to get rid of R12 entirely. My interepetation of the law is that it is not legal to convert back to R12 once a system has been converted to 134.

This makes a good arguement for not switching to 134.

You may find it dificult to find a shop to change it back for you. In fact I found it impossible to find anybody that would restore it to R12.

To do it yourself, you would have to go into a shop, have the system evacuated, replace the dryer, replace the fittings, flush the system, then have it evacuated and charged with R12. Flush the compressor with the oil you are going to use. You can buy R12 on eBay. Certification is a joke. Take a test online and pay a fee. the important part is that you have no excuse for doing something stupid if you get caught. You can't say you didn't know any better.

This is of course, not only a lot of hassle, but also illegal, so don't do it.

A dryer designed for R12 is not compatable with 134. I doubt you could find one anyway. Anything made in recent years would be 134 compatable, and work fine with R12. If your system is R12 and the parts guy says all they can get is a dryer for 134, smile and say "Thank you that will be fine." "O" rings also, You could get cheaper ones, but go ahead and use the green things for R12.

As to the number of hours that the system has to hold a vacuum, it is on the certification test. The system must hold 25 inches for at least 2 hours before recharging or something like that. I think it was 25, the 2 hours part I am sure of. Overnight is better.

Perhaps I did not state this clearly.
 

Perhaps I did not state this clearly.
Roughly 2% system fluid capacity loss.

I have a 55 gallon vacuum tank pulled down to 30 inches mercury, with a high capacity two cylinder 220V 50 amp 20 hp commercial vacuum pump, recovering to a 30 pound high pressure cylinder.
I can suck a car or truck system dry in seconds.
Pulling the charge that fast also sucks most of the free oil out of the system = 98%...
The O rings I get in 1000 unit selector boxes.

On two of my cars I did not change the O rings because they where going to part out in less than a year.

I will not replace the R12 compressor shaft seal until it begins leaking R134A, in many cases it is cheaper to replace the compressor when it fails.

I use 32 ounces of Acetone while flushing the average system, and that stuff is dangerous to work with.

WHunter, I still can not figure out what you are intending to say...

The loss of system efficiency due to changing to the less efficient R134a molecule is widely accepted as about 15 to 20 percent. This is why I thought your 2 percent was a typo...that you meant 20 percent.

"Roughly 2% system fluid capacity loss."
Since you state you can pull 98 percent of the oil out of a system with your equipment.... is this 2 percent related to that statement? And perhaps stated backwards ?
98+2=100 ?

Since AC refrigerant is measured by weight... since it is only liquid under certain conditions in which seeing how much fluid is present is not usually possible I did not think you were referring to the refrigerant.

Your use of the term ' capacity' as compared to amount in the system made me think your original statement ( which it looks like you have edited out ) referred to cooling capacity of a system.

kidney stones are hell
 

They have me on so many drugs to kill the pain, it is no surprise that I am not being clear.

Roughly 2% system OIL capacity loss is what I was trying to say.

The loss of system efficiency due to changing to the less efficient R134a molecule is widely accepted as about 15 to 20 percent.

In general; that is true, a very skilled climate control mechanic can achive only 13% loss.
This is not possible in a general shop environment, it takes too much time, effort and training.

Using 134 I get 40° F vent temp on a 90+° day with high humidity.

My trick is to fill the system on the low side... plenty of bubbles in my dryer's viewer.

On a 126 two 12 oz cans seem to work well..

Very nice
 

Hello Frank Mulone
RE: Using 134 I get 40° F vent temp on a 90+° day with high humidity.

What is your high side pressure running?

Re: Very nice
 

I sold my gauges in 1996 .....;)

I have an R4 compressor. AUX fan is on. Compressor fairly quiet..

Many bubbles in sight glass...

Abner,

Just wondering if you got it charged.
How did it turn out?

Why does R134a need the "green things"? What is the difference?

on a related note, This is a sort of incredibly dumb question but I'll shoot. Its a 300D Turbo. 1982. I am trying to recharge is retrofitted with the 134a system. It just needs a new charge. The bottle on the back reads do not plug into top end service valve. It may explode the can. Duly noted. I plug it in the only valve I see with the 134a fitting (this is the valve slightly towards the windshield of the radiator, topside near the valve cover) and try to connect it and tap the can, but no go. There is no pressure from the can to the AC unit. I am reading the pressure gauge on the can that comes with the 134a recharge hose. No pressure. Hmm. Spider sense is going off. What do you guys make of this?

The high-side fitting is hiding below. I think it's on the right side, deep in the guts of the engine. The low-side is on top, where you were connecting. If the fittings are installed correctly, you can't connect to the wrong one as they are different sizes.

I don't quite understand "no pressure from the can to the AC unit." Can you elaborate? You should see something when releasing refrigerant from the can.

Is this one of those cans with the throw-away dispensing valve included? Are you sure you read all the directions and have popped any tab or anything that may be required to release the contents? Does the car have the proper snap-on r134a fittings, not the r12 threads?