North American Turbocoupe Organization

R-12 to R-134 Conversion
andrewjs18 Offline
R-12 to R-134 Conversion
By Matt St. Denis

Converting your air conditioning to R-134 is not that complex of a procedure if you understand the basic operating principles of the system and have some time to do it.  I converted mine when I replaced my heater core and 3 years later it still runs fine on R134. It’s kept me cold in the 105* summer of the central valley California, humid 80’s through the Midwest to Carlisle, PA; and defrosted the damp foggy windshield Northwest winters.   No, it’s not “colder than my ’06 this or exactly 35* at the vents;” though I have never had to keep it on high longer than 10 minutes to initially cool down the car and then only occasionally have I needed it on medium.  

There are some other products on the market that claim to be a direct replacement to R-12 needing no retrofit however I could not find much information about their real world use, nor have I encountered any professional shop that has used them.  R-134 is considered by many to be one of the safest refrigerants.  R-134 is the only refrigerant recommended by Ford for replacement to R-12 on the HR-980 compressor.

At the end of the document I describe what I feel is the best practice for the whole procedure, a brief tutorial of what I learned (that I can remember) about the theory of A/C operation and my personal observations three years later.  If you are completely lost as to the principals of how air conditioning works, read the simplified A/C explanation at the bottom.

Items needed:

Spring lock coupler tool. There are inexpensive plastic ones that do the trick. They are round with a lip and   expand the spring that is holding the tubes to the compressor and condenser.   See for more information

Accumulator/Drier.  This is not compatible with R12 and you must buy an R-134 compatible drier or your entire system could be filled with desiccant.  I got mine at AutoZone for around $50. Drive your car there, look at the pictures in their book and pick the one that looks just like yours.  It was a direct fit for me.

A/C manifold gauges.  I suggest buying the A/C manifold gauge set, and not just the single hose sold in parts stores.  You can find a set at a good price from Harbor Freight, and you will get your money’s worth if your system leaks.   A good one will go down to 30” vacuum (1 bar) low (blue) side. Note the bottle valve in the middle of the hoses in the picture does not come with the set. See below.


R-134 can adapter/fill valve.  You’re A/C  gauge set does not come with the valve that screws onto the can so you have to buy one at your parts store.  The fill hose from the gauge set will screw into this valve. It also allows you to only use a partial can of R-134 since you can close the valve and remove it from the gauge set.

Compressed air Used to blow out the condenser and evaporator with the flush agent as well as operate your vacuum pump.  A water separator is required on your hose.

A vacuum pump. Get a compressed air vacuum pump for $10 from Harbor Freight, or rent one. It should provide at least 20+” constant vacuum, preferably higher.

A turkey baster Use it to get the flush agent into the tubes, condenser and evaporator.  Or better still, I found a suction wand that uses compressed air. You can put the suction tube into the bottle and it atomizes the liquid into the compressed air and has a narrow spray nozzle

3 or 4 cans of R134 refrigerant – without the oil.  It’s important you measure the oil yourself. Too little and you will burn up the compressor. Too much and it will start to pool in your system, affect performance and could blow the seals of your compressor.  The oil is mostly suspended in the R-134, and not meant to pool in the system.

The following can be found at an A/C shop.  I was referred to an automotive A/C supplier and found the correct seals, adapters, oil and flush in one spot for less money than a parts store or a mechanic’s shop.

Flush liquid.  I don’t remember exactly what it was, but it was stinky and about $40 for a 1 liter size bottle.  Tell them what you are doing and buy what they give you.  Highly recommended you get, and do, the flush. Make sure you get the stuff compatible with both R-12 and R-134.  

Esther oil. 2 bottles.  It comes in 12 ounce bottles if I remember correctly .About 11 ounces are needed for the system, the other bottle will be used to flush the compressor. Ester oil is compatible with both R-134 and R-12. It keeps your compressor lubricated.   This might also be available in a parts store.

Green R-134 o-ring seals. May or may not be available in a parts store.  I waited until I had the system apart and brought the old ones with for comparison shopping.  The accumulator/drier comes with seals.

New fill adapters/fittings for the R-134 tubes used to fill and check the system. R-12 tools and A/C line fittings are not compatible with R-134, and these new fittings that screw onto the existing ports are required by some law.  This is usually in a package that contains oil and maybe a few assorted o-rings at the store. The package I bought did not have all the correct o-rings I needed so I returned it. The A/C supply shop had everything for less money and tons of free information.

Optional: New garter springs.   I didn’t replace them.

Cleaning out the system

Step 1:
Discharge your R-12 at an approved shop location. Do not let this highly dangerous chemical vent to air, let a shop vacuum it out for you. They might even give you some money for it.  If it’s already empty well then you saved a step.  While you’re there ask them what they suggest about the conversion.

Step 2:
Disconnect your lines using the spring lock tool. The tubes don’t come apart easily at all so make sure you have your tool in the end of the tube good so it expands that spring. The tube has a lip at the end, and the receiving end has a spring that wraps around that lip to hold it on. Your spring lock tool expands the spring so it is not holding the lip of the tube anymore.  Bring lots of patience and 2 hours expectations to this chore.

Take all of the old o-rings off except the ones on the accumulator/drier (the new one comes with seals) and go shopping for new ones if you haven’t already.

Step 3:
Remove the compressor from the car and place it tube side down over night to let all of the oil drain out of it. Turning the compressor also helps to pump out oil. I placed mine on a couple of pieces of wood placed on a bucket and let it drain for a day while I did other things. Get as much of the old oil out as possible.  .  Do not flush with the flush agent or used compressed air.

Step 4:
Back flush the condenser with the flush agent; it is best to remove the condenser for this.  Using the turkey baster, squirt a few ounces of flush into the bottom tube (outlet to lower hose) on the condenser.  If you found a sprayer set it to draw just a little at a time so you’re not spraying too much flush. Find an old appropriately sized hose and put it on the tube on the top port of the condenser (inlet port from receiver/drier). Put the hose in a spaghetti jar lid poked with a hole or something to catch what comes out.  There will be mist and stinky fluid and oil blown out this tube.  Don’t breathe it!  I poked a large sized vent next to the hole for the hose on the jar lid, then took an old torn t-shirt with one cut hole for the hose and screwed it onto the jar. This helped keep the fluid in the jar and not vaporizing out.   Use lots of compressed air and blow it out good. Repeat again with another few ounces of flush.  Then reverse your ports and flush it the other way out.  I used around 60lbs air pressure.  Use a water separator on your air hose to minimize water vapor being introduced in you’re system.

Do the same to the evaporator (I took it out of the heater box while I replaced the heater core).

Then do the high side hose that connects the condenser to the compressor (not the low side with the cylinder-that gets replaced).  Back flush first by starting on the end that plugs into the evaporator. Do the same to the lower long hose that has the orifice in it. Start flushing backwards with light air.  I used 20lbs air pressure. Do this a few times, and then blow out this tube the other way with flush.  The idea is to remove as much of the old R-12 oil and junk out as possible out of all the parts.  I could find no recommendations to replace the fixed orifice tube.

Now everything should be nice and clean.  Blow everything dry to get as much flush out when you are done. You should have used most of the bottle they gave you. Start light and go around to all the parts a 2nd time if you have some flush left.  When done blowing everything dry, cap all the ports and hoses with rubber bands and plastic wrap or whatever. Try to keep exposure to air at a minimum while the rest of your heater core is completed.

Wear protective clothing, eyewear and some gloves. What will come out is very smelly and can’t be good for you. Don’t breathe the vapors.

Put it back together

Step 1:
Put about 1-2 ounces of the new Ester oil into the compressor inlet tube. Spin the compressor a bit until the oil comes out. Do this a few times to clean out the compressor, and then drain all of the oil out as best you can.  Now put about 1-2 ounces in the compressor, turning it again to distribute.   It should not be flooded full, however.  Put 2-3 ounces of oil in the evaporator, holding it so the oil drains into the rows.  Put 3-4 ounces of oil into the condenser in the same manner.  Put an ounce or so into the liquid (fixed orifice) line.  Try to use around 9-11 ounces total split among everything. Put the most in the condenser, then the evaporator.  Get some rubber bands and plastic wrap on the ends of everything to keep moisture out when you are done.

Step 2:
Put the condenser and evaporator back in their spots.  Do not put the o-rings on the condenser or evaporator yet so they don’t get damaged.  Put the compressor back on. You can leave the 2 lower high pressure hoses out for now.  Complete your heater core change and assemble the car back into running condition.   Ensure again that your condenser and evaporator tubes are capped adequately while you replace your dashboard unless you plan to vacuum and fill it the same day of assembly. Install your new accumulator/drier.

Step 3:
Remove all of your hose caps/rubber bands including the accumulator/drier caps and apply a small amount of oil on the o-rings and the tube to lubricate the assembly.  Attach the accumulator/drier to the top evaporator tube on the firewall, and then plug the other end into the compressor.  Put your seals on the liquid hose, evaporator and condenser ends and attach all the ends.   Ensure and that you don’t damage the seals, and that the springs are locked on the hose. Yes it is a tight fit.   Don’t forget a coat of oil on those parts also.

Vacuum and fill

Step 1:
Put your new R-134 adapters on the fill ports:  high side fill port is the bottom tube connected between the compressor and condenser and low side is on the accumulator/drier cylinder. Replace the pressure switches you had to remove at each end also. Use Teflon tape. The left picture is the high side (from compressor to condenser); the right picture is the low side attachment on the accumulator/drier; with R-134 fittings.


Attach the high and low side hoses from your  A/C gauge set to the correct ports and ensure the valves on the gauge set are closed.   Connect your vacuum pump to the fill hose, the middle one on the A/C gauges.  The vacuum pump I bought does not have a gauge, so I fed it the maximum 90psi. Once the pump is hooked up and sucking, open both the high and low valves on your gauge set and let the vacuum pump suck the system down for a minimum of 2 hours. The more vacuum the better, most suggestions were to have 30” vacuum (1 bar). You will probably have to “adjust” some of the connections to seal if you don’t get vacuum readings after a minute or so.

Vacuuming the system helps all of the o-rings seal. But the most important part is to provide enough vacuum so that the water boils out and you remove as much water as possible.   It is then used to ensure the system is sealed by reading vacuum loss over time.

After two hours minimum (the longer the better) turn off the gauge set valves and turn off your vacuum pump. Listen for any squeaks or hisses that indicate a vacuum leak. Wait at least 2 hours and ensure the system is not losing vacuum. I suggest letting it sit like this over night and seeing if you lost any vacuum.  If you have, apply vacuum to the system again then jiggle and press the hoses to make sure you have a tight seal.    If you didn’t lose any (or hardly any – more on that later), then it’s time to fill the system.  Either way, apply vacuum for at least another hour right before you fill it to get any remaining moisture that took a long time to vaporize out.  There simply can never be too little water in the system.

Step 2:

Make sure your gauge valves are closed and plug the high and low side ends of your gauges back onto the system if they aren’t already. Screw the separate valve you bought into the gauge feed hose and then screw that onto a can of R-134. Twist out the fill valve all the way up so the poker is not showing and screw on a can of R-134. Then twist the valve all the way down to puncture the top of the can, and twist it back up to open the can. Open both your high side and low side valves on the gauges and turn the can upside down allowing your vacuum to suck as much liquid in as possible.  If the first can empties, close all the valves and replace the can to continue.  When the pressure on your gauges no longer increases and it appears the can and system pressure are equal…



The high side pressure will soon reach over 100lbs and WILL explode your can of R-134 if allowed into the can resulting in serious personal injury and property damage. The high side valve on the gauges should NEVER be opened while the A/C compressor is running..PERIOD!

You do not need the valve open to get a high side pressure reading.

From now on all filling will only be on the low side, the compressor will suck the cans dry.

Start the car and place you’re A/C in the MAX position and the blower on high (EATC users turn down the temp as low as it will go and select high).  Roll your windows down to vent the cold air. Use the blend vent/floor function to provide as much air flow as possible. When the 2nd can is empty leave the car running with A/C on and simply close all the valves, replace the can. This can take about 30 minutes or more. I usually put the can in a bucket of warm water to accelerate the process.

Step 3:
On the 3rd can you should start to pay attention to the pressure readings you are seeing. On a cool day I usually place the can in warm water to speed up the process.  As the system fills you will also notice the compressor running cycle gets longer as it has more refrigerant to work with.  If I recall correctly I used about 3 ½-4 cans. The compressor should run for around 10 seconds each cycle. The pressure of your system is an indication of how much R-134 you have in there.  In general, I fill my system until it has about 150-180lbs high side pressure, and around 35-40lbs low side pressure on a 70* day.  The readings will cycle as your compressor cycles on and off, so I take the high readings.  Remember the system pressure will get higher the warmer it is out.  The temperature of the day significantly affects the pressure of your system and needs to be accounted for when filling you’re A/C System.  Don’t give it 200lbs high side and 20lbs low side on a 60*F day, for example, when there’s little heat to take out of the air. It will be a lot higher when it’s 90* out!   A pressure/temperature chart is provided below for R-134 compared to R-12.


At this point, if you like how cold the air is coming out the vents then you are done. You can always add a little more if it doesn’t seem cold enough and your high side pressure is low. Over three years I learned it does leak about 2 cans a year.  R-134 is fairly cheap so I just charge it back up.   R-134 molecules are much smaller than R-12, therefore, R-134 much more prone to leaking.  Mine has always leaked a little. Recently I used a can of stop leak and it seems to be holding much better. I ran the A/C most of the way out to Carlisle and back this year and was never lacking for cool air and defrosted windows.

Pressure discussion:


The HR-980 compressor in our cars is not a very good piece of equipment.  The general consensus was that your system should never see 300lbs on a 110* day in stop and go traffic.  R-134 is not as efficient of a refrigerant as R-12. Your system will not feel as cold as a new car. Newer systems have larger condensers to cool the charge more and also have higher pressure systems for greater evaporation to overcome the shortcomings of R-134.  I have been warned by everyone I spoke to that I should not “chase the cold” as it could destroy the compressor if pressure gets too high on a hot day.  

I also tend to fill mine on the low side of what I could get away with considering how weak the compressor is to begin with. Again, I don’t need ICE COLD to be comfortable and I consider 3 years to be a good track record considering the horror on the professional shops face when I told them what compressor I had.  No sense in stressing the system.

NOTE: some resources have suggested adjusting the pressure valve that the low side switch is on (accumulator on the firewall) about 1/8 to ¼ turn to lower the pressure that the switch cycles the compressor off.  I did not do this.

Here is a few links on the discussion:;t=011815;t=014188;t=008909;t=007930

This website has tons of information, and where I got the pressure/temperature chart from. It was an active page when I did this 3 year ago but has since gone offline. I was able to find it at; however some of the links may not work.

Pressure/Temperature relationship:

Note the pressure table below. Below about 60*F R-134 has a lower pressure than R-12; above 60*F it has a higher pressure. I do not know at what volume this pressure is for the table below (probably some industry standard such as 1cu. ft), but it provides insight as to the behavior of R-134.  Since R-134 is a higher pressure than R-12 at real world temperatures, you would need less R-134 than R-12 to keep the same system pressure.   I have found information suggesting from 60% to 85%.  And that’s in pounds. How many pounds is a 12oz can?  I just follow the system pressure and how often the system cycles to know if I need more.

Simplified A/C Explanation:

Compressor: Located on the engine driven by a belt, the compressor moves the refrigerant around the system by compressing the evaporated gasses back into a liquid in order for them to be evaporated again.  It is operated by the low pressure switch.

Condenser: Located in front of your radiator, liquid refrigerant flows through the condenser from the compressor to be cooled down, before being evaporated, to maximize efficiency. Clean fins, a properly operating (passenger side) fan and good airflow go a long way to a cold air system.

Fixed Orifice Tube:  Located in the lower hose that joins the condenser and evaporator. This small tube meters refrigerant to be evaporated, and its restriction creates the high pressure side of the system.  The outlet of the orifice tube is the low pressure side. This tube is not serviceable and the hose would need to be cut to get it out, requiring a new crimped hose.  I have not found any professional resource that said replacing the orifice tube is required.

Evaporator: Located in the heater box where warm cabin air is passed over it and cooled. The evaporating refrigerant takes the heat from the air as it evaporates.

Accumulator/Drier: Located on the firewall connected to the evaporator and compressor, this cylinder removes any moisture from the refrigerant.

Refrigerant is a liquid that boils at a very low temperature, well below freezing.  Under pressure it can also be a liquid, just like a can of air for your computer. When liquids evaporate they take the heat out of their surroundings. The can of air you use to blow the Doritos off the keyboard gets cold as you use it.  Evaporation is the basic idea of how an A/C system works.

Refrigerant gas is compressed into a liquid state when the magnetic clutch is energized and engages it to the pulley driven by a belt.   The compressed-to-liquid refrigerant is hot so it gets cooled in the condenser (in front of the radiator – the condenser is a radiator too). The hot liquid refrigerant raises the pressure in this area. The high (pressure) side fan switch (between intercooler and compressor) turns on the secondary (drivers side) fan when the pressure exceeds about 310lbs.  Cooled refrigerant under high pressure leaves the condenser through a pipe to the lower fitting for the evaporator (in the heater box) at the firewall.  This pipe contains the fixed orifice tube, or expansion valve. The orifice tube is just a restriction in the hose to only let out a certain amount of refrigerant into the passenger compartment. This fitting is a small tube the right size to hold refrigerant at pressure behind it so refrigerant stays (mostly) a liquid under high pressure while releasing the right amount to the evaporator.

While the orifice tube is blocking the refrigerant pumped by the compressor creating pressure, the compressor is also sucking the refrigerant back to it on the return providing a very low pressure on the outlet side of the orifice tube. The restricted refrigerant immediately loses pressure as it leaves the orifice and it evaporates as it is going through the evaporator.   It is now in the low pressure side of the system.   As the liquid rapidly evaporates it takes the heat away from the hot air being blown over it in the climate box, much like a heater core heats the cold air in your car. The low pressure switch (on the accumulator) turns off the compressor when the pressure gets below a certain point, about 25lbs. The lower the pressure, the lower the temperature of the refrigerant.  This prevents freezing the evaporator core.

The now vapor refrigerant has taken the heat from the air in the car and is being sucked through the accumulator/drier on its return to the compressor. This is the silver cylinder screwed into the top port of your evaporator and connects directly to the compressor.  It is filled with a desiccant to remove any moisture from the refrigerant. The low pressure switch (on the accumulator) turns off the compressor when the pressure gets below a certain point, about 25lbs. The lower the pressure, the lower the temperature of the refrigerant. The now vapor refrigerant is again compressed back into a liquid, cooled by the condenser, and evaporates again after the orifice tube taking more heat from inside your car.

raingram70 Offline
Junior Member
I worked in HVAC for a year or so. I was told that R404 residential freon was identical to R12, and still available. Grain of salt on this info of course, but it bears asking someone smarter than me if they know for sure. Cheers!

Jeff K Offline
404 is a mix of R134a, R125, and some other refrigerant compound I dont remember off the top of my head. It is a substitute for R22, NOT for R12!!!
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
11 Crown Vic Interceptor
14 Toyota Camry (wifes car)
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized

coastie Offline
Junior Member
OK, good article
need a/c compressor rebuild or replacement current unit has bad/blown seals.
And a mount if another compressor.

Jeff K Offline
The HR980 compressor is not rebuildable. All that can be done is replacing the ceramic shaft seal.

10 years ago, I picked up 2 brand new HR980 compressors from ACpartsguys (google them). No clue if they still have any.

I used one HR980 when I rebuilt my AC system 10 years ago, and the second one is sitting in my stock of unobtainium spare parts. I still have a substantial stock of R12 for my 88 TC and 86 Tbird 5.0.

10 years ago Rock Auto had the clutch pulley bearing for cheap.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
11 Crown Vic Interceptor
14 Toyota Camry (wifes car)
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized

BradM Offline
Adding some info to this thread since I just did some A/C work. The car was already converted to R134a by the previous owner but it leaked out and he did not change the dryer.

My 87 TC calls for 2lb 10oz of R12. You are supposed to use about 80% of this when converting to R134a, which is 2.1lb or about 34oz.

The line with the orifice tube is Four Seasons 55602. This comes with o-rings.

The dryer/accumulator is Four Seasons 55630. This comes with o-rings and schrader valve.

The O-Ring and Gasket Kit is Four Seasons (4S) 26715. The kit has plenty of every size needed.

Since you'll have the system open, I recommend you change the high side schrader valve (in stock at any auto parts store).

After some research, I did not add any replacement oil to the system. There were a few teaspoons in the old dryer along with some water.

My pressures were 27psi low side and 245psi high side at idle (78 degrees and 75% humidity) using almost (3) 12oz. cans.

I was able to achieve 42 degrees at the center vent at highway speed (around 60 degrees at idle).

If you're new to A/C work, don't forget to purge the air from the line between your can and the manifold before adding refrigerant to the system. Given the parts I replaced and how long the system was open, I pulled a vacuum for one hour (open both the low and high side valves during vacuum).

My system held full vacuum overnight so I don't expect any leaks. I'm not sure if this is normal but at idle, my compressor stays on and the secondary fan turns on and off to regulate the pressure. I'm running a PiMPx and have the secondary fan set to go on at 205 degrees (which it never hits).
1965 Mercury Comet Caliente; 1968 Mercury Monterey; 1969 F100 Ranger; 1982 Mustang; 1987 Thunderbird Turbo Coupe; 2017 Police Interceptor

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