Bernard

I had a bad A/C condenser and have a new one on order and wanted to find out how much R12 are system holds? I have a 30lb cylinder.

911rudy

From just having my system replaced and charged, they told me that they don't actually use weight or volume but pressure as they add it after vacuuming the system. I'm sure that 30 lbs will be more than enough!

A930Rocket

Isn't the amount located on the air box housing? I'm guessing it's about 48 OZ.

kens911

it's about that when you fill it though you dont do it by pressure like most systems you fill it until the little ball in the bullseye or the dryer starts to float. pressures are always off since the rear deck is open when filling and no air flow through the rear condenser.

A930Rocket

I had forgotten about that little ball in the aite glass of the receiver/drier. I used to fill the system up to the point where there were no more bubbles in the site glass. Also, aren't you supposed to have the rear deck closed (as much as possible) to get air through the rear condensor? A fan like Rudy's would really help here.

kens911

yes but it's really hard to close the deck and fill the ac.

srf506

You just lay the deck down gently on the hoses of the filling system. Its not optimum, but it works. Good luck with it.

911rudy

Just as an aside, you do NOT use the glass sight for 134a. srf506 is correct about closing the lid on the hoses. If you really wanted to be exact you could tape off the gap but when you are looking for a certain high/low pressure, then thats all you need unless the lid is left completely open. It helps to have a target amount but that is not the final measurement. The temps and pressures are the final adjustments.

kens911

you use the sight glass for 134 also the liquid volume is the same just the operating pressures are different in the gas phase.

911rudy

The company that I just went with said that because the volume is less than with R12, you do not use the sigt glass. Here is a reply from Pelican.

You have several options to get your ac system up and running. However how effective of a system you want will depend upon your climate needs; do you use the system often, are you in a hot climate, etc.

With R12 the refrigerant oil was what they call a mineral oil whereas R134a uses either "ester" or "PAG".

R134a requires a different desiccant (what is in your receiver drier) and requires different service charge ports (ref: your schrader valves).

Why you would want to "lubricate your system" .... I don't know. Normally the system is a closed loop system; it does not consume oil alike an engine. The only time you need to add oil is when you have had a refrigerant leak or you have replaced a component. The oil circulates through the system with the refrigerant and constantly lubricates the compressor; the compressor does not have a sump. But I don't want to discourage you from thinking about your systems ac oil... its a good idea since many of our 911's or or 930's have been passed down to many owners and the ac system repair history is vague; in many instances someone may have "topped off" due to leaks however they failed to add oil.

R134a condenser side pressures tend to run on the average (industry jargon) 10% higher than R12. Hence you either use less refrigerant or use a higher capacity or efficiency condenser system.

There is an option for you if you simply needed to add a lubricant other than mineral oil, you could use "ester" refrigerant oil. Esters tend to mix with mineral easier than PAG and it is very common to simply add ester when converting to R134a refrigerant. In a perfect world (you got the time and money) you would flush the system to remove contaminants that collect over the years (drier desiccant break down, compressor break down and hose break down) in the hoses, condenser and evaporator (you don't flush compressors or driers) prior to converting to an alternative refrigerant. However, its a proven fact that flushing is not necessary for a simple R134a conversion.

A "simple" R13ra conversion requires removal of the compressor, dumping of whatever oil remains in it (usually little), replacement of the receiver drier with a new drier that has R134a compatible desiccant (XH7 or XH9 desiccant), replace any o-ring on any port you have opened or component connection you have opened with o-rings made from HNBR (Hydrogenated Nitrile Butadiene Rubber), evacuate system for 3 hours, charge with a nominal amount of 85% by weight of the original R12 charge using R134a (example: if the system originally used 39 weighted ounces of R12 you would use 33 ounces of R134a) and fine tune (add or remove refrigerant) the charge based on an R134a Pressures and Temperatures chart.

Adding R134a to a system that has R12 can be done however its not recommended; when R12 and R134a are mixed together they form a high pressure azeotrope. This means that together their pressure is higher than either by themselves.

Getting back to the basics, a 930 has over 40 feet of refrigerant hose. The original hose is what we call "non barrier"; designed over 50 years ago; leaks or permeates refrigerant over time. So no matter what you will be constantly topping off or recharging your system since the stock hoses simply leak (the leakage rate or permeation rate is based on pressure, temperature and time). The solution is replacement with new barrier hoses.

kens911

yes it says 85% by weight not volume both of my cars that I switched over didnt cool correctly until I had filled them to the midle of the bulls eye. I tried doing it the other way on the turbo because the dryer I got for that one had a really small bulls eye and was hard to see. But in the end I had to unstrap it from the fender well where I could see it correctly. it you use a scale like a lot of shops use and add by weight then of course you would ad 85% by weight if what r-12 weighs hope I was able to clarify a little better. you know like a gallon of gas weighs less than a gallon of water but both still take up a gallon of space.

Bernard

Thanks guys... I will use a scale to add the R12. Looks like it holds close to 3Ibs.

Bernard

I received the new rear condenser and installed it without any problems. I vacuumed the system for 30 minutes and zeroed out the scale. I could only get the system to take 1 Ib 7 oz my high side was well over 300. Inside temperature was only 59 degrees.

Tomorrow I'm going to use the gauges and set it up by pressure. Anyone know what the hi side should read? Say 85 degrees outside temp.

911rudy

I had the same problem when I went to charge my new system and it turned out to be a small piece of metal in the high pressure side of the expansion valve. The orfice in the exp val high side is about the size of a paper clip wire so it doesn't take much to block it. This make for real high pressure because it is not going throught the evaporator fast enough and cannot relieve the pressure to the low side. If thats your problem watch out for over pressurizing the hoses. Remember that a compressor is just a pump and with any pump system you only get a pressure buildup when you get a restriction. That is partly what the exp val does but it should not be that high. We were looking for the low 200's on the high side with 134a. I think that R12 is lower than that.

Bernard

Thanks for the info. How hard is it to change the expansion valve? I also want to replace the dryer.