R134 Refrigerant Capacity?

[kna4977]

How many cans of R134 are needed to recharge a stock original system on a 1972 from empty after vacuuming and sealing?

[Dave]

I would call Old Auto Products, I'm sure they'll know.
817-531-2665

[kna4977]

I don't want to call a company about it. Someone on here likely knows and has recently done it. Please chime in if you know.

[samert111]

R134a is not compatible with a 1972 factory original system that used R12 at the time which is next to impossible to get, and if you did find some it would be obscenely expensive. It is no longer produced and anything out there would be either recycled or old stock.

R134a was first introduced in early 1990's.

[Stocker]

Originally Posted by samert111

R134a is not compatible with a 1972 factory original system that used R12 at the time which is next to impossible to get, and if you did find some it would be obscenely expensive. It is no longer produced and anything out there would be either recycled or old stock.

R134a was first introduced in early 1990's.

This pretty much agrees with everything I have heard & read. You can convert your factory A/C to use R134a, but it does involve changing some of the components.

[Richard]

IIRC the stock R12 charge is 3.25 or 3.5 lbs. R134a charge would start at 15% less, so start at about 2.8 lbs. Hopefully you have addressed the conversion needs. As mentioned you cannot just throw 134a into a stock system. You will be very disappointed as the system will not produce any cool air without proper corrections.

[kna4977]

Originally Posted by samert111

R134a is not compatible with a 1972 factory original system that used R12 at the time which is next to impossible to get, and if you did find some it would be obscenely expensive. It is no longer produced and anything out there would be either recycled or old stock.

R134a was first introduced in early 1990's.

I actually have several cans of r12 on the shelf, however my system has supposedly been converted to 134, but I have my doubts that it was done correctly. What components need to be changed what corrections need to be made?

[RustyPile]

Originally Posted by kna4977

I actually have several cans of r12 on the shelf, however my system has supposedly been converted to 134, but I have my doubts that it was done correctly. What components need to be changed what corrections need to be made?

It's very tackey of you to demand someone do your leg work and/or spoon feed you the information. This conversion is discussed all over the internet.. I'll offer this as starters.. POA valve, schraeder valves, compressor oil. And depending on which one you have, probably the condenser.. This list is not all conclusive...

[kna4977]

Originally Posted by RustyPile

It's very tackey of you to demand someone do your leg work and/or spoon feed you the information. This conversion is discussed all over the internet.. I'll offer this as starters.. POA valve, schraeder valves, compressor oil. And depending on which one you have, probably the condenser.. This list is not all conclusive...

Not sure where your animosity is coming from but I haven’t demanded anything. I’ve done several 134 conversions. I was wondering what might be different about this system that it would need something special so it would work right. This particular system has only had 134 in it at least since it’s been installed during restoration so it’s not really a conversion but it doesn’t seem to cool very well even though it has a charge so I’m wondering what might be the problem.

Usually when I’ve done conversions I would replace the dryer clean or replace the condenser. Most of the time the compressor had some type of issue like a leak so replace or rebuild that. Vacuum it down check for leaks repair as needed then recharge.

[hatzie]

The Harrison A6 should cool properly usung the stock evaporator and c9ndenser if you charge it the right way.

You need to do douche all of the old mineral oil out of the whole system and fill the compressor & system with PAG or Ester oil. I drain out the compressor overnight and then measure how much oil came out and refill it with the same amount of PAG or Ester. The service manuals will tell you how much mineral oil went in the entire system so you subtract what you poured into the compressor from the system charge and fully charg the system with the remainder of the system charge oil.

Refrigerant charge is a fun one because it's not a 100% reliable method to use the original charge X the conversion factor.

Back in the late-90s on fidonet aircon forums there was a user called JungleEddy.
He pontificated at length about how to get a proper charge using a non-standard refrigerant.

Again I don't have the posts Eddy has referenced on Vacuum, Flushing, Oil Supply, Leaks etc and unless some other enterprising soul saved them they have disappeared into the electronic æther along with fidonet and dial-up BBS systems. I expect Usenet forums will soon follow them into the mists of time. :-(

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Posted by JungleEddy on September 05, 2001 at 08:17:44: via: or 66.25.151.188

More important stuff.

How to charge an A/C system.

Note: This method will work for any automobile A/C system regardless of refrigerant type. The pressures I list here will only be correct for HC’s.

I have been trying for the past couple of weeks to come up with a “system” that would allow just about anyone to properly charge their A/C system. While this method I have developed is not fool-proof, it yields the closest thing to a perfect charge I have found. I have tested it on three “non A/C” mechanics in the past few days with great success.
First: If you have not read my previous post on vacuum, flushing, oil supply, leaks and fans etc etc, please do so now. You still need a properly assembled system to get proper cooling!

This ENTIRE process makes a few IMPORTANT assumptions!!
1. The ambient air is OVER about 84 degs.
2. You have a set of A/C gauges
3. You do not take shortcuts.
4. You are able to read and comprehend enginsh.

This process will work down to about 80 degs ambient air, but will be MUCH MUCH easier to over charge below 85 degs ambient air!! Relative high side pressures will be lower at 80 degs ambient and pressure drop after wetting the condenser will be less dramatic.

Pull a hard vacuum for a minimum of 15 minutes, 60 minutes is perfect. Static charge the system to about 65 psi while the engine is NOT running.

If you have a low pressure cut out switch on your system you will need to adjust it down to 18-19 psi sometime during this process. Personally, I find it easiest to do this about midway (now) through the charging process. Remove the connector from the switch and turn the adjustor screw about 1 full turn counterclockwise from its factory position. (counterclockwise is less psi, clockwise is more psi, 99% of the time) Start the engine and turn on the A/C, recirc, max fan, and engine at idle. Max fan is important, since it will help keep the evaporator from freezing as you charge. Charge the system slowly (if you have to!) until the compressor stays on fairly continuously at IDLE. The adjustment I illustrated above should give you a cut out psi of 12-18 psi. Watch your low side gauge and SLOWLY increase engine rpm. The low side pressure will drop slowly but substantially because you are still undercharged. Watch it drop from 20+ psi down through the teens and carefully note where the compressor cuts out. Return the engine to idle and pull the connector to the cut out switch and adjust it accordingly. Try this several times until, as the engine is slowly revved the compressor cuts out at about 18-19 psi on the low side.

The Charge:
Bring the engine rpms up to a continuous 1200-1800 rpm. Begin to add refrigerant (if you have to) SLOWLY until you notice that the air at the vents is noticeably cooler than the ambient air, say at about 65-75 degs or so.
At this point grab your garden hose and hose down the condenser; soak it once only. Your pressures will drop dramatically. The high side should drop below 150 and the low side should drop low enough to cycle the compressor, or if the switch is temporarily “jumped” the low side should be well below 20 psi. I prefer at this stage to jump the connector to the pressure switch to keep the compressor running continuously. It makes the process go much faster, but you risk freezing the evaporator. Now, watch the system pressures rise as the water evaporates and the heat in the system and stabilizes and equalizes. This can take a long time if you have a mechanical radiator fan. The point where the pressures remain relatively constant is called equalization.

Here is the key:
(After wetting the condenser) As you are watching the high side pressure rise from 160psi through (potentially) about 205psi the LOW side should REMAIN from 21-24 psi. If the high side never sees 145+psi you are still low on charge as long as the ambient is 85 degs or above. If as the high side needle swings through 160psi the low side is still below 20psi, you will add more refrigerant AFTER wetting the condenser again and dropping the pressures. Keep doing this until the low side remains at 21-24 psi while the high side swings through 160psi and finally settles at equalization (no more rise) Keep the engine rpms constant and wait for equalization (or close) each time before wetting and charging. If you are going carefully and slowly you could see a high side over 225 at equalization BEFORE you reach a full charge. The high side will DROP as you come closer to a full charge. Be aware that if you over-charge, the high side will climb again and never come down.

Note: If the ambient air is above 95 degs, stop watching the low side after the high side climbs past 205 or so. Especially if you have weak fans.

Note: Take your time and wait for equalization and water evaporation off the condenser before adding refrigerant. An overcharge can occur with no more than an extra 1.5 ounces of refrigerant!!

You can double-check your work at any time (and I suggest doing so) by waiting for full equalization and stabilization of pressures. Then, carefully MIST water into the condenser SLOWLY SLOWLY dropping the system pressures and watching for the same readings on the gauges as listed above.

When finished you should have a sweaty return line all the way back to the compressor. When the return line begins to feel chilled over the first portion of its length, you are approaching full charge. Do not forget to reconnect the low pressure cut out switch!

Do not consider your vent temps accurate until the vehicle has been driven for about 10 minutes at moderate highway speeds!!!! Idle low side pressure should not exceed 40 psi (34-38 actual) if everything is working well; good fans etc….

The idea here is that the compressor should NOT cycle when ambient air temps are above 81-84 degs.

Interesting note for tech heads: If you are charging SLOWLY. You will find at first that the high side will be at a higher pressure, after equalization, on a low charge than at a correct charge! Remember, raised heat = expansion and/or pressure.
Why: (basically)
Within a certain range, the pressure in the condenser (high side) is MUCH more affected/determined by the temperature of the refrigerant than its volume.
ALL THINGS BEING EQUAL, the condenser has the ability to lower the temperature of the refrigerant passing through it “X” amount and no more. The compressor, in compressing the refrigerant, heats or raises the temperature of the refrigerant “Y” amount. Lets say the temperature of the refrigerant entering the compressor via the return line is “Z”. So the final temperature “T” of the refrigerant that gets to the orifice/exp valve is: Z+Y-X=T
If we could lower the value of “T” the entire system would work more thermally efficiently and at lower pressures on the high side. So, ALL THINGS BEING EQUAL, you could 1. get a larger condenser and raise your “X” value or 2. lower the value “Z”.
A full charge on an A/C system will not only have enough refrigerant in it to keep the evaporator “chilled”, but JUST ENOUGH that the line leaving the evaporator and returning to the compressor will also have substantially cooled refrigerant in it THUS LOWERING YOUR “Z” value!! Hello!!
Note: Over charging will allow actual condensed refrigerant (liquid) to make it all the way back to the compressor. As we all know, you cannot compress a liquid…boom/screech.
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[PbFut]

Now that was an answer worth cutting pasting and saving.

[RichardJ]

>>douche all of the old mineral oil out of the whole system and fill the compressor & system with PAG or Ester oil.<<

Maybe I can explain that a little differently.
Mineral Oil is not compatible with r134a.
Mineral Oil is not compatible with PAG.
Ester Oil is compatible with Mineral Oil and with the R134a.
You can't drain or flush the old mineral oil completely out of a compressor without rebuilding it.
You use the ester oil in a compressor that ran mineral oil after draining and cycling by hand to get as much out as you can.

New compressors all seem to come with PAG, so you just have to flush the rest of the system.
New dryers and accumulators are made to work with either Mineral or PAG, but they can't be flushed and you were planning on replacing anyway.
Condensers and Evaporators should be flushed in both directions with AC Flush Solvent.
The flush is sometimes hard to find at a good price. I've never got it at the same place twice. I always have to shop around every time I need it.

[hatzie]

Originally Posted by RichardJ

>>douche all of the old mineral oil out of the whole system and fill the compressor & system with PAG or Ester oil.<<

Maybe I can explain that a little differently.
Mineral Oil is not compatible with r134a.
Mineral Oil is not compatible with PAG.
Ester Oil is compatible with Mineral Oil and with the R134a.
You can't drain or flush the old mineral oil completely out of a compressor without rebuilding it.
You use the ester oil in a compressor that ran mineral oil after draining and cycling by hand to get as much out as you can.

New compressors all seem to come with PAG, so you just have to flush the rest of the system.
New dryers and accumulators are made to work with either Mineral or PAG, but they can't be flushed and you were planning on replacing anyway.
Condensers and Evaporators should be flushed in both directions with AC Flush Solvent.
The flush is sometimes hard to find at a good price. I've never got it at the same place twice. I always have to shop around every time I need it.

Good info on oil.

I usually replace the PAG oil that's in brand new compressors. PAG absorbs moisture so I want the oil in the compressor to be the freshest stuff I can manage.

[Sheepdip]

Originally Posted by hatzie

Good info on oil.

I usually replace the PAG oil that's in brand new compressors. PAG absorbs moisture so I want the oil in the compressor to be the freshest stuff I can manage.

Trust me I am no expert or claim to be... but I would think pulling the required vacuum to charge the system would remove any moisture in the supplied compressor oil. But there is absolutely nothing wrong with changing it out.