Just for comparison, I used 36 oz of R-134 in that failed conversion I attempted 16 years ago, but I'm not sure what the R-12 charge was for that TXV system with no suction accumulator, and high-side receiver/dryer. It was the amount the Volvo retrofit called for after "upgrading" the evaporator in that system. It cooled for a couple weeks before it grenaded, by chance, in front of a Volvo dealership. They quoted $1800 at the time. I cut the belt and drove it home. I was never aware of the 80% guideline.

Also, I still have one of those old Robinaire heated graduated cylinders :)

http://cleanflametrap.com/retrofit.pdf
--
Art Benstein near Baltimore

Grandchildren are God's reward for not killing your own children.

hi david,
that's great having a high side port.

a variable orifice would be a higher grade orifice tube, allowing better cooling at lower rpms.

jumping the switch is just a test to see if it gets cool by forcing the compressor to stay on and avoid rapid cycling.

from a ford bulletin board but applies to all a/c units:
" Did you have High side and Low side gauges on it if so what were the readings when it was on?
Cycling can be several things Low charge will cause the Low side to drop below 10psi and open the low side switch, Too much refrigerant or a blockage will cause the high side to get too high and the high side switch will open. Bottom you need both gauges to properly diagnose it . If you see frosted spot on one of the A/C lines there may be a blockage."

http://www.techsupportforum.com/forums/f155/ac-compressor-cycles-on-and-off-269985.html

forcing the compressor on, you might be able to qualify your problem by observing any icing on any of the lines.

i think you are very close to narrowing down your problem. you'll get it done.

regards,
byron golden

HI,

I would say you are finding out why I don't really care for the cheapness of these systems, let alone, their lack of fittings to save even more costs. The reduction of fittings started long ago. There are none on domestic refrigerators. They used the excuse to reduce leaks and tampering to do it.
My new to me 1993 has a very special factory one from what I can tell. It's all crap!

I'm sorry you are having trouble. I feel this is not your first rodeo doing this type of work.
I agree it does sound like you have a restriction. The high side gauge will tell what's happening along with the observance of the low side gauge to show flow.
I'm also concerned that Auto Zone computerized reference book does not take into account that you are converting to 134a and that the person punching the keys knows what to look for in the process.
If it does not have a flag on the orfice, if it gets noticed, you get a standard issue of "normally ordered with!"

I have also read about reducing the amount of 134a used to work across these coils.
Some how they, I don't know who, came up with this 80% less amount.
I do know for a fact that 134a operates with a 10% lack of efficiency to begin with when compared one pound to one pound of each.
Maybe it's because of the lesser amount and but nothing to do with its capability of moving X amounts of BTU's per pound of liquid. One or the other can or must be the cause the loss?
Water is our best refrigerant per pound. That is next to liquid hydrogen and it takes buckets of water to put out fires! Don't ask me which one in the water but H2O puts out a fire as the heat gets moved through evaporation.

It's is for the above reasons is why the size of the coils and fans. They had to be revised larger going into the nineties. There were already many complaints, to Volvo, that their systems using R12 were not comparable to our domestic cars in cooling. Now, They had to deal with the 10% loss to boot.
.
I worried about oil for those motorcycle sounds. I was not sure if it is shipped inside or outside the compressor due to which refrigerants used.
The sound might mean the compressor is just laboring.
At least you didn't lift the HP safety!


Two ounces of oil is "about" the right amount since you also cleaned out the tubing in both coils.
The desiccant bag is going to get coated with the most of it, once it all gets blowed all around.

Having or Adding too much oil causes headaches though.
It's worse on capillary tube or orifice systems as it interferes with charge balance that's based on volume of refrigerant changing sides.
Capillaries are really a fixed system device. Used to primarily be first "cheap" and it has fixed heat load exchange rate limitation. The Most common place you find these was in the home refrigerator due to the millions of units produced.
Unfortunately cars they have reached these proportions.
Unknown to most people, Refrigerators are made and sold into specific climates. There are tropics versions and another for colder climates.
They vary the charge by an ounce or so to compensate for drops in wattage efficiency because the two coils will rise higher due to the constant heat they operate in.
Today's high efficiency refrigerators come with warning about operating them in hot places like garages. They are flirting with smaller motors and tricks of using dampers. It's written in my latest refrigerator booklet, "Doing so can void warranties!"

I have wondered or curious of what's on the labels under the hoods of 90's Volvos sold at the equator. Even though A/C is considered a high temperature system, in that, it is Not food preservation critical. They make tropical radiators and fans, don't they?


IMHO, a variable orifice adds a "variable twist" to the charging aspects.
The gadget is "doing its on thing" based on a properly sized spring to slide the opening back and forth.
I have never used one and probably never would just on the fact there is no receiver to place excess liquid. I don't see the slight gain to be worth it's failure possibility.

Like you said, trash, it comes from lots of places and occurs in hose systems where in refrigerators with solid tubing, it does not. Their dryers are mounted solid in the line and refrigerators seldom move.
The desiccant is a wonderful source of trash as it is a beaded granulated powder that is getting vibrations from a car. I have found this grit all around an orifice's screen.
Who ever said the beads can it not wear down over time from the rapid flow of gas droplets. I see it being a torrent of rain in there.
Dryers used to be only in the high side. The inventors of refrigeration had reasons for that, besides having the moisture condensed in with a hot liquid. The idea is to stop it before going through the expansion device where it freezes.
I think you running a vacuum pump for 24 hrs is over kill, unless you didn't get below 29 inches mmHg. Time and heat is needed to good a job. You had the time going on for sure!

It is good that you are using a sight glass type charging cylinder. Wish I had one since I retired from company funded tools.
I have to use a homemade make shift recovery unit now. It's made of Ice buckets surrounding empty refrigerant bottles. I hate losing any my stash of R12.

It sight glass takes the guess work out of what's left in the hoses and that the true liquid weight went in. Once it's out in the line you "milk" the manifolds lines to move it all in except vapor of course.
They are ideal for these type of volume dependent systems, in fact, almost mandatory.

It's amazing for me to see into the automotive world with it left up to guess work without good specifications available. The word "proprietary" hurts everyone over greed.
These specifications come from the laboratories and on into journals and training manuals. At this day and age of our refrigeration world it's silly not to have the knowledge just out there!
It took a lot of us "old farts" to work through through these problems and make things work. It seems very sad to let people starve in two ways!

When you added the oil did you pour it straight into the accumulator inlet or add it by filling up a charging line?

If you put it all on the high side, by directly inside the compressoror or say directly into the condenser line or hose, it will take some time for it to clear the expansion device and balance out. Oil can lay in a low spot or at the beginning of end of turns and act like a restriction in either one of the coils.
That rapid pull down on the low side is the first indication of a restriction. A slow high side drop in pressure is the same. You may consider cycling the unit for a while to see if pressure equalize faster over some time before doing a refrigerant recovery.

Sure interested in what you discover either way!

Phil

The label by the radiator calls for 2.07 lbs. of R-12 for a B230 engine. I initially charged the system with 2.07 x 80% = 1.6 lbs. or 22 oz. The car would quickly go into low pressure cutout. I added 4 oz. more, which resulted in the current condition. I used an old style charging cylinder to measure the charge. The low pressure cut out is what is baffling. I wonder if Auto zone gave me the wrong variable orifice, or if there is trash in the system. I feel I really flushed the system well. I am considering removing the variable orifice and installing the regular orifice.