Looks like vintage stuff. I think you said in an earlier post that you replaced or refurbished everything but the expansion valve. That may be the culprit. The expansion valve sets the superheat of the Freon after it has left the evaporator. Usually 10 F above what is called saturation. For example, if you measure 40 psi on the gauge and look at the chart you will see somewhere around 43 F. That is the saturation temperature/pressure and represents that fine line where the Freon can exist at either a gaseous state (if the pressure dropped just a smidgen) or liquid state (if the pressure increased just a smidgen). Same with slight increases or decreases in temperature and it can flash back and forth. The expansion valve bulb senses this temperature at the evaporator outlet and adjusts the flow of Freon to make sure the gas temperature is 10 F above that fine line - in the example 53 F. This makes sure that only gas and no liquid goes back to the compressor. The superheat comes from the top part of the evaporator. The bottom part holds boiling liquid refrigerant to a level determined by the amount of charge in the system and the top part still gets heat from the air coming in and heats the Freon gas temperature 10F above the temperature when it left the surface of the boiling pool of Freon by the time it reaches the outlet pipe. Too little charge and the liquid pool of Freon drops and too much charge and the liquid pool of Freon rises. Other things can affect this, but this is basically what happens. The expansion valve has a gas in the small copper line that goes up to the bulb that will expand or contract with temperature. The gas pushes against a diaphragm in the top of the expansion valve and there is a spring on the other side which counters the pressure in the copper line. If you were to take the expansion valve out and look in the bottom, there is a hex socket that can adjust this spring tension. It is not uncommon for these valves to either freeze up or have limited movement due to corrosion. The corrosion comes from moisture in the system. R-12 is a chlorinated flouro-carbon. You have three chances to make acid when combined with moisture - Hydrochloric acid (a by product of its production in the first place), Hydrofluoric acid and Carbonic acid. Which acid comes out is dependent on what other contaminants are present in the system and how the Freon broke down chemically. This is why it is so important to get the moisture out and why there is a desiccant in the system to help keep the moisture at bay.
Every part in the system including the expansion valve is new or rebuilt. That doesn't necessarily mean it's good though. Many parts while new are NOS so they could be 40 plus years old. If there is a problem with this system it is most likely the expansion valve but I'm not going to open it up and lose the charge until I'm sure there is a problem. I haven't had a chance to investigate any more but hope to this weekend. I'll post what I find so everyone can continue to point me in the right direction.
Questions for Mikec: 1)Have you ever tried to re calibrate and expansion valve for R134? I did experiments and found that if I counted the turns on the hex nut in the expansion valve, turning it in till it bottoms, and multiply the number of turns by .6 it seems to work for R134. For example: if it was set at 5 turns at the factory I would set it to 3 turns and that seems to work for R134. I did a motor home that was set to 10 turns at the factory and I reset it to 6 turns and it worked great! 2) Have you ever tried gutting an expansion valve and putting a variable orifice tube into the evaporator inlet tube (with dimples added to the tube to stop it from falling all the way in)? Variable orifice tubes are calibrated for R134 and cost about $30. 3) Do you think the clutch in an A6 compressor is up to the task of a cycling system? Some one told me an A6 clutch is too small for a cycling system. Thanks, Phil (also an engineer but not in refrigeration)
1) Yes and it was a significant failure. I saw your post about that and thought your approach might work over mine. I read on the web about R-134a retrofits that if you turn the screw counter clockwise 6 turns it will magically convert a R-12 expansion valve to a R-134a expansion valve. The lesson learned - don't believe everything you read on a blog.:error: Since R-134a is cheap it wasn't an expensive lesson. It took 6 cans of R-134a to get the superheat right and my head pressure was up to 400 psig. I read on the chevelle board about the napa valve and it took 3 cans and driving in Georgia during August is tolerable again. 2) I thought about that as a way of further simplifying everything and for a cycling clutch system that will probably be the better way to go. The expansion valve system does need more time to stabilize. What I have observed (based on load) is that when the system first cranks up, the pressure in the evaporator drops rapidly and trips the compressor clutch pressure switch. So there is a bit of a rocky ride until things stabilize - usually about 3 to 5 minutes. Where do you find this orifice? 3)I am using the pro6ten compressor. I still have my original a6 but i was concerned about removal of the mineral oil so I have one if someone is doing a concours restoration. The pro6ten clutch is larger than the A6 - that's for sure so there may be something to the clutch being too small for cycling. To keep mine from cycling too much is I set the set point on the pressure switch down to about 25 psig. That is just below freezing so it helps with the short cycling startup issue and acts more as a safety than a control switch. If I had to do over again I might have just had my POA valve recalibrated for the R-134a and skipped the cycling function. I did take the car up to Charlotte NC last Friday - about a 450 mile round trip and the a/c did fine and the outside air in the afternoon was 87 and humid. That was quite the interstate romp - everyone wants to race you to bench mark themselves against 70's muscle.:TU:
It's not 6 turns. Turn the screw in from the factory (R12) setting and count the turns, then multiply the number of turns by .6 (6/10) and turn it back out that many turns. This is nothing I read in a blog, it's an experiment I did my self through many iterations. I had my 72 C10 set-up like that for the last seven years I owned it, and, I sold it nine years ago and it's still working (that's 16 years if you're keeping count). I did several other systems like that and it was not a failure. The variable orifice tube was developed to retro-fit the fixed orifice systems of the 80s to R134. The orifice tube is about 3 inches long and drops in the evaporator inlet tube which has three dimples to stop it from going too far. The fixed tube can be pulled out with needle nose pliers and the variable tube drops right in. I've converted these systems with the original fixed orifice in place and the vent temp is maybe 55 degrees, a variable tube drops it to 46 degrees. I assume it has either spring loaded ball or metering rod inside. Most auto part stores sell them (I haven't bought one in over 5 years) I'm going to try one in the next A6 system I do. The expansion valve will need to be gutted to do this. Our older GM evaporators have the right diameter inlet tubes for the variable tube to fit in, just add a dimple or two to the side of the tube about an inch from the end so it doesn't go in too far in case you need to replace it some day. They make a solvent designed for flushing all components , including compressors, of R12 systems prior to converting them to R134 to remove the mineral oil. It's about $50 a gallon.
I did actually use a set of gauges that allowed me to view the vacuum which was between 29 and 30 and an industrial vacuum pump. I have my own gauges now specifically for r12. I'm concerned about the pressures and possibility of air in the system as well as the longevity of the system since I had less of a clue about what I was doing to start with than I do now although I'm still a novice on this. I would like to vacuum it back out and start over, but I haven't been able to find anyone that is able to recover r12 and I don't want to shell out the big $$$ for the machine myself so I'm not sure what to do there. Any suggestions?
I don't know if you are a fan of the TV Show "Moonshiners" and understand boiling and condensing alcohol in a still, you can do something similar with refrigerant to get it out of the system and separate the air by condensing the R-12. When you do this, the fact that air is a non-condensable is now to your advantage. Two things will be hurdles to jump over - one finding a DOT container - those 30lb cans that will have the proper fittings for your hoses (R-134a containers do not) and the other is having enough of your vintage R-12 on hand because you will lose some. R-12 and R-22 come in these DOT cans and a shop may have one or two laying about that they may let you have or lend. You will need to vacuum the can as low as you can and close it off. Then place the DOT container in a tub of ice on top of a bathroom scale. Dry ice will be much better for this operation since it is 182 degrees colder than frozen water and can likely keep your DOT can under vacuum through the whole operation. Connect you gauge set to the system through the middle port and purge the lines a little bit (10 seconds) to get the air out of the gauge set and then as it is purging connect the DOT can sitting in ice still holding a vacuum to the system. Open the valve on the can. You may want to start your car and get it good and hot without running the A/C system to increase the pressure of the R-12 in the system. You will want to roll up the windows and run the heat on full in recirc mode to get the evaporator hot. The reason for this is that refrigerant will migrate to a "cold" spot in the system and condense. You want the pressure in the system high to drive the refrigerant out. You will need to do this for some time - maybe 30 minutes to get as much out as possible. Using dry ice will make it go faster. After you have run this way for a while, look to see if the scale has gained 3 to 4 pounds, keeping in mind that dry ice will evaporate directly to the atmosphere. If so, you can now isolate the DOT can by closing the valve on top of the DOT can. Take it out of the ice and let it warm up. Don't agitate the can to allow it to fractionate. Air has a molecular weight of 28 and R-12 has a molecular weight of 120, so the air will rise to the top of the can if it is allowed to stand un-disturbed. Keep your gauges connected and look for the can pressure to rise to around 40 to 50 psi - this will take hours possibly. Then open the low side manifold valve and let a little gas vent out of the center port - maybe 15 seconds or so to make sure the air is out. Now you should have in your possession pure R-12.
I have too much oil in my system which is causing the high pressures, bogging and poor cooling. I have a limited budget and limited tools. What's my best option to get it straightened out with what I have to work with? I have a vacuum pump, gauges, r12 and oil. I'm thinking about dumping what I have and going with envirosafe refrigerant because it's cheaper and compatible with r12 r134 and the oils used or do a 134 conversion. Thoughts?
You can recover the R-12 as described above or dump it if you have enough to recharge if recovery is too much hassle. To get the excessive oil out you should pull the evaporator, the hose with the muffler and condenser out of the car and buy some A/C flush which is available at the local NAPA or Autozone. You'll probably need 3 cans or so. The evaporator can come out by only taking 1/2 of the suitcase apart. A little tricky but can be done - you'll need to take the passenger side valve cover off. Run the flush in the evaporator and condenser until it runs clear. I also used water to flush out the flush and then finally compressed air. You can also dump the oil out of the compressor but I doubt that is the culprit. Put the system back together and pull the overnight deep vacuum which will get any moisture out and try again.
I used the enviro safe refrigerant and it cooled like a freezer. If you were to use it id still say change the txv you will be amazed at how it will cool. Deep vac (break) the vac with the new freon and change and enjoy.
I've heard good things about it as far as cooling, but researching it more raises the concern of flammability. It's a hydrocarbon refrigerant.....a mixture of propane and butane...and that's ok and an ideal replacement for r12 if there's no chance of fire and in a system that's immobile or designed for a flammable refrigerant, but there is that risk,...so for safety reasons I need to go with a refrigerant like r12 or r134.
If you are scared about the risk of carrying around a small amount of propane, then are you scared of the 20 gallons of gasoline you are carrying around? This idea of flammable refrigerants being dangerous is total nonsense. The refrigerant in the system is not mixed with oxygen so it CAN NOT blow up. If you do have a leak, propane diffuses very rapidly into the atmosphere. So unless you are holding a lighter right up to the leak, there is no chance any of that refrigerant will have the chance to ignite. Gasoline is WAY more dangerous. When it leaks it pools. When propane leaks, it just goes away.
X2. It has an auto ignite of 1500... So no Sparks and such well ignite it. And you would have to hold a flame right at the leak for it to ignite. Don't be afraid of it. It has lower saturation point and operas way better at lower pressures than any refrigerants used today. Operating at lower pressures means it had less chance of leakage.. Just to give you an idea of what I'm speaking of... All said and done my high side pressure was 100psi and low was 37psi hires that sound?
I would like to use enviro-safe or a similar product....it's much cheaper....,but unless all the info on the forum below dedicated to automotive a/c is b.s., it doesn't seem like a good idea. A fuel system is designed from day one with the necessary features and safety factors to handle the flammable fuel. The A/C system is not. http://www.autoacforum.com/messageview.cfm?catid=2&threadid=18988 https://www.google.com/search?ie=UT...utoacforum.com&sitesearch=www.autoacforum.com
Forum of people that never used it and you know there's already a few JA starting trouble in a thread somewhere. I won't tell you anything but using it was good for me
Propane is probably the closest to an ideal refrigerant that is out there. Zero ozone depletion, smaller pressure rise across the compressor leading to lower compressor horsepower per ton of cooling, etc. So why don't we use it everywhere? This revelation about propane is not new and has been known to the industry for decades. Safety concerns. There is an ANSI/ASHRAE standard 15 which is the safety code for refrigerants. Propane as you can imagine is at the top of the list for flammability. If you have a building with a large chiller holding a few hundred pounds of the stuff and the building catches fire - well you can see why we don't use it so much. You may say what about cars? There is only a couple of pounds. The reason is that only the vapor burns. Liquid gasoline and liquid propane do not burn. But in an accident if your gas tank leaks, the gas stays a liquid at atmospheric pressure and only the vapor that has evaporated from the surface catches fire. Propane will all flash to a vapor if the ac piping is broken in an accident. It does need a spark to ignite so that is the chance you take using propane. Will the pipe break and will there be a spark in an accident? Your call. Personally I went the r-134a route. To answer your other question about the compressor oil needing to be drained. I don't think it is the culprit because the compressor oils internally from a sump, suction tube, shaft mounted pump and hollow shaft to push the oil to the swage plate and front shaft seal. Unless there is a serious piston seal leak, the oil stays in the compressor except for a little vapor that gets by the piston seals like in the engine itself.
The system is over by 2 ounces. As an alternative to pulling the evaporator could I take 2 ounces out of the compressor?
You could try pulling the condenser and use 1 can of flush and see what you get out. The condenser is a whole lot easier to pull.
