Engine Custom A/C. How to determine correct amount of freon?

FastDriver · Jul 17, 2019

Guys, I've just purchased all of the tools I need to do an a/c job right, but I have no experience doing it, myself.

I've had my black car to several shops to recharge my a/c system over the years, but each time, the freon has either leaked out, or has blown out of the high-pressure safety valve on the top of the compressor. I bought a black light and glasses, and did a cursory glance at the compressor, condenser, and lines, and the only place that I found a/c die is all over the top of the compressor. I assume that was from the high pressure release valve. I further imagine that the over-pressure incidents that have occurred may have been due to the fact that my system is non-stock.

I still have the stock compressor, condenser, accumulator, and evaporator. However, the lines are not stock, and they are sizeable compared to stock. I thought perhaps this might have an effect on the amount of R134 that the system should take. My question is, how would I go about determining the right amount to use? If possible, I'd like to be smarter about it than trial and error. I thought, perhaps, that the pressures in the lines and temps produced by the system might provide the guide to determining the appropriate amount. Can knowledgeable a/c guys weigh in on this? Would the oil be the same as stock or would it increase commensurate with the amount the freon increases?

FastDriver · Jul 17, 2019

Am I safe to go by this?
I found this on an a/c pro product website:

JD1964 · Jul 17, 2019

If your system is currently empty, put a new dryer on it, vacuum it down and see if it holds. If it holds, charge with the amount listed on the compressor label. Do it by weight. That's a good starting point. Then you can check the pressures after getting it up and running. Do you see where oil has leaked? If so, adding some to compensate might be a good idea.

Mustang5L5 · Jul 17, 2019

I'd go by pressure drop across the orifice.

However I'd find the specs on the mustang system vs generic specs.

RaggedGT · Jul 17, 2019

And make sure you are running the correct orifice tube and 134a compliant low pressure switch

Noobz347 · Jul 17, 2019

When I did my R134a conversion it was serviced to 80% of the capacity from the original R12 chart:

1989-1993	All Engines	R12	40.00	Mineral	8.00
1986-1988	All Engines	R12	40.00	Mineral	10.00

Of course, mineral oil is also not used and I do not recall if PAG was compatible with the OEM compressor seals or if I used some other compatible replacement.

FastDriver · Jul 17, 2019

John Dirks Jr said:
If your system is currently empty, put a new dryer on it, vacuum it down and see if it holds. If it holds, charge with the amount listed on the compressor label. Do it by weight. That's a good starting point. Then you can check the pressures after getting it up and running. Do you see where oil has leaked? If so, adding some to compensate might be a good idea.

Good idea. I have not yet checked the system. My new a/c tools are still being shipped. I'll check and if the system is empty, do as you say. I also purchased an o-ring kit and if I do disconnect anything, I'm going to do them all.

Mustang5L5 said:
I'd go by pressure drop across the orifice.

However I'd find the specs on the mustang system vs generic specs.

Would that be the same as high side - low side pressure, or is there some other measurement to take?

nickyb · Jul 17, 2019

R12and134a use different oil. Do yourself a favor and flush the old oil out then use the correct for 134a oil.Or do as i did and use es12a ,this ref. Is comparable with both oils,and is better for eviorment,and cools better.I've used this in my daily Fox for 5+ years,I'm way happy with it.Check it out for yourself.It can be installed with out a vac.also.

FastDriver · Jul 17, 2019

For situational awareness, and sorry for not posting this up front, I converted from r12 to R134 in 2005. Also, I know I've replaced the compressor, condenser, and accumulator since then. I'm pulling out my file to see if I have any old receipts for more info.

Mustang5L5 · Jul 17, 2019

FastDriver said:
Would that be the same as high side - low side pressure, or is there some other measurement to take?

Yes, same thing. The difference in pressure is due to the flow through the orifice. If the low side is too low, add refrigerant. However you want to pay attention to high side as a blockage will cause it to spike.

jrichker · Jul 18, 2019

Here's some more help in the A/C arena...

Currently, I am running Enviro-Safe R12 substitute, and it works very well. eBay has 3 can package for $25 + shipping. It does not require any vacuuming or purging of the system, and is a real aid to the DIY guy looking to save some $$. The warning say it is flammable, but so is gasoline...

no matter what refrigerant you use, you will need to replace the accumulator/dryer; cost is about $55-$95

Try eBay for some R12, it is running $20-$30 a can. You need 3 each 12 oz. cans and 6-8 oz. of R12 compatible mineral oil. The R12 compatible oil is like $20 a quart when you can find it. You may be able to find a combination can of R12 and oil together which may be cheaper than buying a quart of oil..

It is illegal for a company to sell any refrigerant other than R134 to a person who does not have an EPA 608 or 609 certification. That includes Freeze 12. However, individual sellers like those on eBay and, not affiliated with a store often do not ask for any certification information, they just want prompt payment.

See http://www.epa.gov/Ozone/title6/608/overlap.html for more details

R134a Air Conditioner Conversion and recharge instructions

Revised 14-Jul-2013 to add Low Pressure Cutout Switch adjustments for R134 & Freeze 12

Color Legend:
R134 specific items and instructions are in red text
Freeze 12 specific items instructions are in orange text
Note: R12 is available on eBay. Use the Freeze 12 instructions except use the R12 36 oz refrigerant charge with R12 refrigerant
Items and instructions common to both R134 and Freeze 12 are in black text

Tools and materials you will need:

Gauge set for recharging = $20-$120 – check out the pawn shops for a bargain before you pay retail.
See Harbor Freight Tools for an inexpensive gauge set.

Vacuum pump – I use an old refrigerator compressor = $20- $40 at used appliance stores, or go to the Dump and get one for free. Be sure to have some R12 compatible oil handy to keep it lubed up properly.

O ring seal kit = $8.

Replacement accumulator/dryer assembly with hose $55-$75

Alternative refrigerant – Freeze 12 – it will allow you to skip flushing the system and reuse the original accumulator/dryer under certain conditions:
1.) If the A/C system has not been open to air for more than an hour or so.
2.) Or if it hasn’t out of refrigerant for more than 5-7 days and the system is till sealed up with no open or disconnected lines. You need to be able to hear the hiss when depress the valve core in either one of the service ports. That tells you that there is still pressure in the system, which keeps out moisture and contaminants.
If either of the above is not true, you must replace the accumulator/dryer assembly.

Freeze 12 refrigerant: $15-$16 per 12 Oz can on eBay. Get 3 cans, 2 for the initial charge and 1 spare for a top off charge.
Use R12 compatible mineral oil, 6-8 Oz. This may be difficult to find or expensive (~$20 a quart). Sometimes eBay will have the oil/R12 combination cans, which have about 4 oz. R12 and 2 oz. oil in them. If you go this route, add the R12/oil charge first, then add the cans of R12.
Do not use PAG oil in a Freeze 12 system without flushing it first.

Freeze 12 refrigerant charge= 26-28 Oz plus 6-8 Oz R12 mineral oil on an empty system. A recharge may only require 2-4 OZ of R12 mineral oil if you only replaced a line, hose or seals.

A/C systems that have had a compressor failure must be flushed. Failure to do so will result in the floating trash left behind from the compressor failure destroying the replacement compressor.

R134a = $11-$16 a can – takes 2 cans.

R134a PAG or Ester compatible oil = $7-$12 for an 8 oz bottle .

Pump to force cleaning fluid through the system $20-$50 (may use compressed air to do the same thing).

R134a charging adapter = $13 (I cut mine up to use it with the R12 gauge set that I have had for a long time).

Plastic tools to disconnect refrigerant lines - 1/2" & 5/8" = $4 each.

Flushing agent - Discount Auto Parts has some flushing solvent in a 1 gallon plastic bottle - try that first. Or use Mineral spirits = $4-$5 a gallon, tetrachloroethylene =$5-$10 a gallon, takes 2 gallons of either one.

Miscellaneous hoses and fittings to adapt the flushing pump to the system, and the R134a adapter to the R12 gauge set = $15.

R134 Refrigerant charge is 26-28 Oz plus 6-8 Oz of PAG 100 oil.

R134 Conversion Instructions:
I did a R134a conversion on my 89GT, and used all stock parts. You will need to replace the dryer/receiver (about $75 if you get the one with the hose made as part of the unit), and should replace all of the rubber "O" ring seals as well. You will need to drain all of the oil out of the compressor and replace it with new R134a compatible oil.

R134 instructions (skip this if you use Freeze 12)
Keep in mind that to fulfill the requirements of the EPA, you are required by law to recover any refrigerant that still remains in the system. How (or wither or not) you accomplish this is up to you. Connect the charging gauge hoses to the service ports on the A/C (red gauge = high pressure, blue gauge = low pressure) and open the valves on the gauges to dump the remaining refrigerant (if any) into your "Freon recovery system", whatever it may be. Disconnect the charging gauges since you are finished with them until you are ready to fill the system with R134a. Next comes the nasty part – in order to get all the old oil out of the system, you will need to flush it with special flushing solvent, or mineral spirits (ok) or tetrachloroethylene (better, but may be hard to get). If you leave the old oil in place it will congeal and reduce the heat transfer in the condenser and evaporator (read that it won’t cool good) and possibly damage the compressor.

Disconnect the compressor and remove it from its mount to flush it with cleaning solvent. Pour about a cup of solvent into the suction port and turn the compressor center hub about 10 turns while shaking the compressor to move the solvent around inside the compressor sump. Drain the flushing solvent out and continue to turn the center hub by hand to force out any remaining solvent. Then fill it with oil: add about 6-8 oz of the new oil to the compressor large suction fitting. Turn the compressor center hub about 20 turns as you turn the compressor face up and face down to distribute the new oil inside the compressor. Catch and replace any oil that comes out of the compressor.

Connect the pump (I had an electric sump pump I bought for $20) to the hose from the high-pressure side of the compressor. Alternately, you could use compressed air to force the cleaning fluid through the system. I didn’t like to do this since compressed air has lots of moisture in it, which is death to A/C systems. Pump the cleaning fluid through the system and let it come out the hose that was attached to the old dryer/receiver. I used 2 gallons of mineral spirits and pumped it all through the condenser and evaporator. The expansion valve is located near the firewall in the high-pressure line of the evaporator, and may cause the cleaning fluid to trickle through the lines at a very slow pace. You may want to pump cleaning fluid through the evaporator and condenser separately to speed up the process.

All refrigerant types
Next comes the changing of all the old "O" rings so that the chances for leaks is minimized. The new R134 compatible O rings are green colored, so be sure that the replacement O rings are green. Use the plastic connector tools to separate the lines, place the extended collar part of the tool so that it faces the large part of the connector and push inwards: this expands the spring so that you can pull the tube apart. You may need a helper to push on the tool while you pull on the tubes to separate them. Install the new "O" rings: be sure to coat them with new oil when you put them in. Install the new dryer/receiver, refrigerant service port adapter on the compressor, add about more 4oz of oil to high pressure line and tighten up all the lines. You may have to add more oil when you do a system that has been flushed or new R12 installation. The total oil charge should be 6-8 oz. for all types of refrigerants. Close the hood, start the engine, let everything get warm under the hood, but don’t add the refrigerant or turn the A/C on. Connect the charging gauge hoses to the service ports on the A/C (red gauge = high pressure, blue gauge = low pressure) and open both valves, then connect the center hose to the vacuum pump. The purpose of this exercise is to heat up the system so that when you vacuum it all down (yes, you will need a vacuum pump- mine is an old refrigerator compressor), that all the air, vapor and moisture from the cleaning fluid vaporizes and is removed from the system. Vacuum it down for about 30 minutes, this should give you about 28" of vacuum or more inside the A/C system. I have a vacuum gauge "T" connected into the vacuum pump line so that I can accurately watch the vacuuming process. This is a good time to take a soda and sandwich break since it doesn’t go faster if you watch it.

the R134a service fittings on the system: the red goes on the high side and the blue on the low side. This will help others identify that a R134a conversion has been done on the system.

Typical low pressure side R134 coupling

Typical high pressure side R134 coupling

Charging instructions for all refrigerant types:
Remove the electrical connector from the dryer/receiver and jumper the two connections inside the wiring harness side of the connector together: this allows the compressor to engage in spite of low pressure/no gas in the system. Close both charging gauge valves, and then disconnect the center hose of the charging gauges from the vacuum pump and connect it to the refrigerant can tapper. Put the refrigerant can in the can tapper and screw it down with the can tapper valve closed, then open the valve. Loosen the hose at the center connection of the charging gauge set until the refrigerant squirts out: this purges the line of air and moisture. The refrigerant is added through the low pressure side of the system, so open the low pressure gauge valve to add the refrigerant. Start the car and take note of the idle speed, then set the idle speed up to about 1200-1500 rpm, and turn the A/C on inside and set the fan speed on high. Watch for the pressure on the low side to drop off as you are filling, and the refrigerant can will get warm and stay warm. This tells you the current can is empty and needs to be changed for a fresh one. Before you disconnect the can, be sure to close the valve on the refrigerant can tapper.

Watch the high side pressure on the charging gages and regulate the adding of gas to keep the high side pressure under 350 psi. You will probably need a fan in front of the car to keep the readings below 350 psi. I had to put the refrigerant can in hot water while I was charging the system with it, or else the can got so cold that it quit flowing. Use caution when you do this so that you don’t get water in the charging adapter when you change the cans.

R12 Pressures when charging is complete
When you have added the 32-36 oz. of gas, the high side will read about 250-300 psi and low side about 28-38 psi. No adjustments need to be made to the low pressure cutout switch.

Freeze 12& R134 Pressures when charging is complete.
When you have added the 24-28 oz. of gas, the high side will read about 250-300 psi and low side about 18-28 psi.

Freeze 12 & R134 Low pressure cutout switch adjustment.
The low pressure cutout switches are adjustable. They should be set with the low limit about 18-21 PSI, the stock setting is about 25 PSI. Remove the wiring connector and there is a screw slot in between the connector pins. Turning it clockwise increases the trip pressure where it cuts off and counterclockwise decreases the trip pressure. I believe that each 1/4 turn counterclockwise lowers the cutoff pressure by 1 PSI.

After Charging refrigerant instructions, all refrigerant types
Turn the idle speed back to where it was, turn the A/C off, disconnect the charging gauges, and re-install all the caps on the service ports. Remove the jumper from the low pressure switch harness and plug it back on the switch connectors.

R134 only
Then put the R134a Service Sticker on, secure all the loose wiring on the system and you are done.

The typical sticker looks like this, yours may be different.

I hope it cools good, mine doesn’t get quite as cold as it used to driving around town.

Thanks go to WWW.ACKITS.COM for some of the graphics.
Check out their website for parts and the Auto AC Forum.

The above technical note is for informational purposes only, and the end user is responsible for any damages or injury. The end user bears all responsibility for proper recovery/disposal of any R12 refrigerant.
I have EPA 608 and EPA 609 MVAC certification. And yes, you can shortcut the process, but there are negative factors if you do. Sooner or later, something will cease to function like it should. Shoddy work is a time bomb ticking away, waiting to explode.

FastDriver · Jul 18, 2019

@jrichker

Do your recommended doses take into account the differences in my system? Do completely different lines make no difference in the amount of refrigerant?

jrichker · Jul 18, 2019

FastDriver said:
@jrichker

Do your recommended doses take into account the differences in my system? Do completely different lines make no difference in the amount of refrigerant?

They are mostly guidelines to give you a starting point; the temperature/pressure chart you posted is your best guide.

Ray65-71-73 · Jul 22, 2019

jrichker said:
Currently, I am running Enviro-Safe R12 substitute, and it works very well. eBay has 3 can package for $25 + shipping. It does not require any vacuuming or purging of the system, and is a real aid to the DIY guy looking to save some $$. The warning say it is flammable, but so is gasoline...

I have been piecing together systems and using Enviro-Safe for at least a decade. I just finished off a 50# cylinder and bought two 30#. I have used it in systems that were originally R12 and R134. I am using it in the modern compressors I am using to replace the old stuff.

If the system has been open I do evacuate but not to an extreme.

I add liquid to the low side, while running, until the gauge is at about 35#

I finally tested something that based on my use and understanding about Enviro-Safe, I thought word work; propane. As a test gas it costs $3 a gallon rather than $3 an ounce. And, it is an excellent refrigerant. So far I have not put it on the road because I just got an Enviro-Safe re-supply.

FastDriver · Jul 22, 2019

Propane sounds crazy to me. I'm imagining the hi pressure relief valve blowing a pound of propane into my engine bay.

jrichker · Jul 23, 2019

FastDriver said:
Propane sounds crazy to me. I'm imagining the hi pressure relief valve blowing a pound of propane into my engine bay.

Vacuum down the system and don't overcharge it and the likelihood of this happening is no more common that a failure of the O rings in the fuel line couplings between the engine and the chassis.

FastDriver · Jul 23, 2019

I think I'll steer clear of this one, guys. In my car, I've had it blow down from the high pressure line twice.

The thought of a minor front end collision is a guaranteed loss of the condenser, too. Nah, explosives and flammables are a little too risky, IMO.

Blown88GT · Jul 23, 2019

FastDriver said:
I think I'll steer clear of this one, guys. In my car, I've had it blow down from the high pressure line twice.

The thought of a minor front end collision is a guaranteed loss of the condenser, too. Nah, explosives and flammables are a little too risky, IMO.

What about a rear end collision which is more likely? Get an EV & you won't worry about it. (LOL).

FastDriver · Jul 23, 2019

I've been hearing about Lithium batteries in Teslas burning up, too.

You can't get rid of the fuel tank, but I suspect that it's potential of lighting off is much smaller than propane next to headers potentially 1200* headers. Also, fuel tank isn't pressurized, which makes the difference between an explosion and a fire, not that you'd want to be in either.

And, regardless, you're introducing a 2nd fire/explosion hazard when the only reason seems to be money, and a few bucks at that. Nope... Not for me. Knock yourselves out. If it works for you, then great. I'd need a lot more knowledge and familiarity with other people doing it before I'd consider it. Just seems like a bad idea. A home A/C, maybe.

Ray65-71-73 · Jul 23, 2019

First, the reason I tried it was because I have long suspected that Enviro-Safe IS propane.

And I don't use alternatives for money. It is for performance and versatility. Enviro-Safe, and possibly propane, works in both R12 and R134 systems, so I don't need to mess with "conversions" and it works better.

We don;t seem to worry about gas leaks. We treat them as a simple nuisance. But when gas leaks it comes out as a liquid and stays liquid for some time. I will not put a rubber fuel line over an engine. But I have had rubber AC lines blow off over an engine. If the whole three pounds of propane leaked out it would flash off and be gone.

Engine Custom A/C. How to determine correct amount of freon?

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