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.

__________________
1980 300SD Manganese Brown Metallic Clearcoat 248k
1979 300SD White 148 k
1984 300D Silver project car for daughter
1982 300D wrecked
1980 300SD 310K not running

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

__________________
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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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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

__________________
_____________________________________________

2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

_____________________________________________

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.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

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.

__________________
69 220D not running
79 240D parts car
80 240D Beater runs everyday
81 300TD temp disabled cooling problem
82 300SD sweet

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.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

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 ?

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.

__________________
69 220D not running
79 240D parts car
80 240D Beater runs everyday
81 300TD temp disabled cooling problem
82 300SD sweet

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.