A/c Conversion Question

R134a Air Conditioner Conversion and recharge instructions

Revised 23-June-2012 to include green R134 compatible O rings used for O ring replacement and R12 charge instructions

Color Legend:
R134 specific items and instructions are in red text
Freeze 12 specific items instructions are in indigo 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.
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)
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.

Both R134, Freeze 12 & R12
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. 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 both R134, Freeze 12 & R12:
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. When you have added the 2 cans of gas, the high side will read about 250-300 psi and low side about 28-38 psi. 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.

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 an 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.

Don't even try to bother with the R12. I am an EPA certified HVAC technician, and it is not even worth trying to put R12 back into your system, only because it is very expensive now a days. The last time I checked, a 30lbs. drum (I do commercial/residential) was roughly about $1600 (my cost two years ago), which is roughly $50/lbs. So, lets go ahead and recharge your system with R12, $150 in refrigerant alone, six months from now one of your seals starts leaking and your charge vents to the atmosphere. Next spring you will need to recharge again. IMHO go ahead and do the 134a conversion, as for your mechanic to do it for $200 properly is not a bad deal at all. I've put 134a in several systems without changing oil, or replacing anything and had it work fine, but the seals will leak, so a recharge every season is necessary, and A/C compressors are on borrowed time that way. So, yes, do the conversion!

tca7291 said:

Don't even try to bother with the R12. I am an EPA certified HVAC technician, and it is not even worth trying to put R12 back into your system, only because it is very expensive now a days. The last time I checked, a 30lbs. drum (I do commercial/residential) was roughly about $1600 (my cost two years ago), which is roughly $50/lbs. So, lets go ahead and recharge your system with R12, $150 in refrigerant alone, six months from now one of your seals starts leaking and your charge vents to the atmosphere. Next spring you will need to recharge again. IMHO go ahead and do the 134a conversion, as for your mechanic to do it for $200 properly is not a bad deal at all. I've put 134a in several systems without changing oil, or replacing anything and had it work fine, but the seals will leak, so a recharge every season is necessary, and A/C compressors are on borrowed time that way. So, yes, do the conversion!

Click to expand...

The problem with putting R-134 in an R-12 system without changing oil is not that it won't work. It will for a while. The issue is that mineral oil, which is what R-12 systems use for lubrication of the compressor, will not circulate in R-143a. So the oil needs to be converted to PAG oil or Ester oil which will circulate in R-134a. Do you need to remove the mineral oil? NO. That is an antique myth that is no longer valid. Vacuuming for about an hour while converting the system will remove some, but the rest can just lay in the system with no issue. The reason the seals leak on an aged system after the conversion is this, first off the seals were probably poo when you converted it #1 because thats why it was low on R-12 and why you are messing with it in the first place. #2 the R-134a system runs at a much higher pressure in comparison to R-12. So old seals that held, are gonna poop out. I convert them all the time using a cheap-o kit. If you want it to last a long time, I usually replace all the easy to get at orings while it is empty, being they cost nothing and it is empty. But its just insurance. And if it was a car I was keeping forever, like my Fox cars, I'd replace the dryer because its cheap and holds a bunch of R-12 oil. Replacing it will help with efficiency, and these cars need all the help they can get, and that is before the R-134a conversion which raises pressures and creates more heat. But the O-rings and dryer do not need to be replaced. Oil does.

I also upgraded the stock O rings t0 the green ones? and put on brackets on the A/C lines by the radiator that hold the lines together, Can't remember who sells them.

And also R-12 may be crazy retail but so many old knuckleheads like me horded it back in the day that you can buy a 30# cylinder of it either full or partial on Ebay for $300.00 everyday. If the system is healthy and I have access to it, I'd much sooner refresh some o-rings and put R-12 in it than retrofit it to R-134. Mostly because it cools so much better in these old systems. The compressor and valving are designed to work with it and at its pressures. Not to mention a pressure increase like you are making when retrofitting can cause 25 yr old hoses and compressors to give up early.

Well if it has been open or dry for any length of time, you need a dryer too. It pulls the moisture out of the system and if it has been open, it is no good. Easy and pretty cheap, however on some of these cars they are part of the hose so it will need a hose. Some are separate. The only oil you would need to replace is what is contained in whatever part you replace. So probably like 2 0z for a dryer. You can dump it directly in the hose. I'd also replace every O-ring that is easy to get to. I'm not sure what the system holds you can look it up if there is no under hood label. Probably like 2.25lbs or something. The only problem here is I'd like to see you have it vacuumed once it is all assembled, before you charge it. Not a deal killer if you can't but it will remove all the air from the system that would contain moisture and also allow you to charge it quickly as it will have a vacuum in it.

The R12 uses a mineral oil lubricant that is not commonly available in auto parts stores. PAG is not recommended to mix with mineral oil. Ester based oil (POE) supposedly is compatible with mineral oil. You may have to find someplace that sells refrigeration supplies to purchase the correct oil.

See http://www.autoactech.com/issues.htm for more information oil oil used in A/C systems.