How to: Converting an R-12 Air Conditioner to use R-134a

[Glacier991]

As warmer weather comes on, there are more and more posts on A/C matters. Many refer to conversion of a pre-94/95 R-12 system over to use R-134a. I have cautioned against simply buying one of the $30 kits and doing it yourself if you have no A/C experience. Simply put, failure to properly clean and flush out all the R-12 residue and mineral oil can, and in time WILL result in A/C failure. Further, you need to properly evacuate the system prior to recharge. Neither flushing equipment nor a good vacuum pump and gauge set are generally readily available to the home DIY person - and shortcuts here can spell disaster. Can it be done at home? Sure. Here's a good link all about it.

http://www.explorerforum.com/Singleton/web/pages/acconvert.html

Happy Exploring...

Chris

Edit by Maniak: Link above updated.. Singleton pages are now hosted on EF.

 

[RiverRat]

Great post.

Also, stay away from R134 "alternatives" or you could explode your explorer

 

[Glacier991]

posted elsewhere but to save someone some time I am reposting it here:

Someone asked me in e-mail how I'd do a conversion or recharge. Maybe, for the 2 cents worth and for those who are considering a $30 drop in kit, it might be illustrative to describe a conversion.

First thing is I check the type of refrigerant in the system. Mainly is it "contaminated" ? I have a tester to do this, it tells me the type of refrigerant and the purity. If it is contaminated I stop. In CA disposing of contaminated refrigerant is expensive, so I do not even go further. Many shops are similar. Remember this when you want to put in the whizbang "SUPER R-12 replacement". Often too then contain propane or butane. BANG!

Ok assuming it passes, I next check it for acid. Why ? It often shows a failing system in progress. If it fails it usually means replacement of major components, but I still proceed. I evacuate the system and recover the refrigerant.

Next I disassemble the hoses to/from the compressor, remove the orifice tube and take out the old "receiver/dryer" or "accumulator" (depending on the type of car and what they call it). I now check for signs of black oil. If the acid was high the chances of blackened oil are high. If I find it, I start by assuming I have a system in failure. Often the expansion valve will already be gunked up with the "black crud".

Depending on the severity, I may try and flush the condensor. If I can flush it clean after a couple tries that is a good sign, if not, I assume the system is a total loss and replace the condensor, compressor and receiver/dryer (which gets replaced in 100% of the cases anyway). If I can flush it clean, I then flush everything I can get to. I often start with alcohol and finish with commercial flush.

Rubber hoses get tossed, and replace with barrier hoses. All o-rings get replaced with barrier ones, they are green in color. I replace the receiver dryer and any other inline filter. Any hint of compressor failure previously and I add an inline filter/dryer to the system.

I reassemble everything, add oil along the way (often to the receiver dryer and as a matter of course to a replacement compressor) up to specs.

I replace the schrader valves with new ones. Any rubber sealed part gets treated with NY-LOG - a terrific sealant. I add new connectors at this point too.

I hook up my vacuum pump and pull an initial vacuum. I stop and watch it to make sure it holds vacuum for 15 mins or so with no loss. If it does I restart the pump and run it for an hour. I feel the hoses and parts to see if any moisture has frozen (it will under vacuum). If I feel cold I stop and let it sit a while and then restart the process. I measure the vacuum and look to pull down to 100 to 200 microns or less (a damn good vacuum, near perfect). I have an electronic vacuum gauge that tells me these things.

Finally I connect my manifold set (used to hook up the vacuum pump earlier and monitor the state of vacuum - and at this point hooked into the automobile system high AND low sides) to a can of refrigerant and add liquid refrigerant to the "HIGH SIDE" with the can upside down until the flow stops. Once it has I disconnect it. I hook up a can to the low side port, and place the can in a coffee can of hot water. I can usually now start the engine and there is enough refrigerant for the car to run the AC. The balance of the necessary charge goes in as gas - can upright and into the low side with the car AC operational. NEVER feed a can into the low side upside down. The compressor cannot compress a liquid and a slug of liquid hitting the compressor can damage it. Once I have put in the required amount of freon (from the manufacturer's specs) I'm done.

I check the vent temps, and they are usually around freezing.

So for a usual job, that's it. Compare that to the instructions of your $30 death in a can kit.

Hope that helps.

(p.s. if I am using a 20 lb jug of refrigerant, I will put the jug on a scale and add the factory recommended amount as the charge, easier, but felt it more meaningful to talk about using cans and not jugs.)

Chris

 

[MikeP]

Chris
Very good description and advice on the R12 to R134 conversion.
I had my 1991 Ford Explorer converted in May 2001 by a Ford dealer and looking at my Ford service invoice, I see the parts charges of $49.95 for Retro Kit (FP # 409996)), $29.95 for R134 DY (FP # 528-205), and $28.48 for R134A (YN-19) - for a total of $108.38 for parts - and so I am assuming some of the air conditioning system parts were changed. I wonder where one can find a description of what these parts were or are?
Your vacuum pump which sucks down to pressure of 50 microns (micron = 1/10,000 of a centimeter = micrometer). Hmmmmm, I am not familiar with the micron pressure unit (I have heard of psig, psia, inches Hg, Pascals, etc). I have some 90 lb two stage Edwards vacuum pumps which go down to very low pressure - but as you know, at these low gas pressures the gas flow is in the molecular flow or Knudsen flow regime which implies one needs large diameter hoses or pipes because the gas molecules no longer flow in the normal bulk flow manner.

 

[Glacier991]

I cannot say I have any idea what you are talking about at the end of your post. I just know that near the endpoint of pulling a vacuum... you get down into a micron range. My pump (a robinaire) will supposed pull down to 20 microns. My digital gauge starts at 400 microns and goes down to 20. I can usually get 50. There are sites on the web that can conver tthat for you, but it's well into an excellent range for any system. I also know the 134 molecules are MUCH smaller than the r-12 and hence the problems with leakage.

As for Ford parts numbers I can give you no clue. Sorry. I do know that Ford has "kits" for conversion, but know nothing about them.

Chris

 

[MikeP]

Chris
I am talking about the units of pressure measurements - like the air pressure in tire commonly uses the psig or "pounds per square inch gage" unit. To my knowledge, there is no pressure unit of "micron". You are probably reading this off of your instrument (digital implies that the readout on your instrument is digital rather than analog - and digital readouts have been around for at least 25 years on pressure measuring instruments) and the actual units might be "microns of Hg" where Hg stands for mercury. The following web site has conversion factors for many pressure units - and microns of Hg is listed.
http://xtronics.com/reference/convert.htm

The stuff I was talking about at the end of my earlier post has to do with gas flow through pipes. At low pressure (i.e. high vacuum), gases do not flow in an ordinary manner like say water through a pipe (bulk flow). Hence when A/C techicians use those small vacuum pumps to pump down the plumbing on home air conditioning or heat pump systems (before the freon refrigerant is added), it is sort of a joke with regards to actually removing all of the air - and hence many A/C systems have a fair amount of air still in the system (and fortunately the systems will still work with the inert air circulating in the system - but they do not work as well as when most of the inert air is removed). However, if there is some freon refrigerant (R12, R22, R134, etc are all different types of freon) in the piping, and one has a good vacuum pump, it is possible to pump down the plumbing and remove the air along with the freon if the pump is allowed to "pump down" for an extended period of time. If you work in the A/C area and understand high vacuum systems, you are probably very familiar with all this.
Thanks for all your posts.
Mike in Seattle

 

[Glacier991]

Mike.. you are undoubtedly correct. Just as we say pull a vacuum of 29 inches, we leave out the unit of measurement. I am sure it is microns of Hg. Vacuum pumps and much newer instrumentation are measured simply in "microns" (check out the Robinaire vacuum pump spec pages for example - most of their pumps are rated at "20 microns").

When you say substantial air remains in a properly evacuated system what level of air molecules are you referring to? It will be well below 1%. It is common practice in some shops to purge a system with nitrogen before evacuating if it is a rebuilt system, to help for just the reasons you mention.

Lastly auto air is not considered a high vacuum application. Other forms of refrigeration (stationary and closed system appliance are considered higher than auto, by far. Once you are in the 400 micron (of Hg.)range you are within the auto air conditioning vacuum arena.
Happy Exploring and thanks for setting the record straight.

Chris

 

[V8BoatBuilder]

Great thread, I want to jump in.

Vacuum Pump Questions:
1) I've done two A/C conversions using the Robinair venturi pump that pulls down to 29mmHG. They both seemed to do well last summer, but I no longer have the vehicles. I may need to do the process on my Mountaineer, so I want to know your opinion on these venturi pumps.

 

[Glacier991]

In the for what it's worth category... Last summer I did a Honda repair ... replaced the compressor and receiver dryer. It was an R-12 system and stayed R-12 (eg. no conversion). I was out of town and it was a favor for a friend. I had forgotten my electric vacuum pump, but he had a Harbor Freight venturi type. I used it, and ran it for about half an hour (his air compressor was starting to overheat. The vacuum looked ok on the gauge set. I refilled it with R-12 and it seemed to work fine, although the vent temps were a tad higher than I was expecting. The charge was correct as per factory specs btw.

Recently he visited and I asked to check to see how the charge was - if there was any residual air. My equip said 2%! I never get an air reading using electric vacuum pumps to evacuate, and then I usually run them for 45 mins minimum, often longer (although the vacuum pumps get real hot too!).

My take on the little venturi types? Ok, better than nothing, but a long ways from an electric one.
My electrics are 1/2 and 3/4 horsepower.

Lastly, those venturi types can use more air than many homeowner air compressors can reliably deliver constantly.

HTH..... Chris

 

[V8BoatBuilder]

Chris, Thanks for the heads up!

I have a question about charging by pressures instead of by weight:

What are the ideal pressures for high/low in your opinion when the system is running optimally? I use the rule of thumb that high side should be 2.2 * ambient degrees F. Sound good? What do you think about low side?

Also, one about flushing:

I used brake cleaner and compressed air to flush the systems when I did the Peugeots, but I've heard other people say use Isoproyl Alcohol, others use a dedicated AC flush chemical. What's your prefference?

 

[Glacier991]

V8... To start with, there is no "perfect high side or low side pressure". The idea is to make sure you have enough refrigerant to expand thoughout the evaporator - that will acheive maximunm efficiency. If I am adding by pressure, I'll generally look for a sightglass, and if I cannot find one I have an electronic sightglass I can use if I get really perplexed, but usually a starting high side of 2.2 ambient is a goodplace to start. I watch low side drawdown with the compressor running and measure and monitor vent temps... You will often see them fall, and once you have too much they will rise. Fine tuning can be frustrating. One of the nice things about totally evacuating is that you have a much better idea since you can find factory amounts for charge and oil. When just adding to a system there is always that nagging Q about oil... on a recharge there isn't.

Returning briefly to the subject of Microns MikeP brought up, I found a pretty good link on the subject.

http://www.aircondition.com/wwwboard/2002Q1/70213.html

Also I have a chart that says at zero vacuum there is a measurement of 760,000 microns. 500 microns equals 29.902 inches of mercury, 100 microns equals 29.917 inches of mercury and 50 microns equals 29.919 inches of mercury, with an absolute pressure PSIA of .001.

Hope this clarifies things.

Chris

 

[Glacier991]

V8 - As I read my reply I didn't want you to think I was trying to dodge your question. a low side pressure should be in the approximate range of 25-45, but will vary as the clutch cycles. It's all about fine tuning.

 

[V8BoatBuilder]

Chris-

Thanks for the replies - you really know your AC!! I've also learned a lot from the forum you posted above, http://www.aircondition.com/wwwboard/index.htm - I suggest that everyone interested in AC systems check it out.

 

[Glacier991]

V-8... I also see I did not reply to your post regarding flushing. Brake cleaner is ok, so long as it is not the chlorinated type. Most of the ones that are not will say so on the can. I like alcohol along the way because it bonds with water and helps remove residual moisture - an AC's enemy. I nearly always follow up at the end with an Ester based flush. If I stay R-12 ester oil and mineral oil are compatible. If I am changing to R-134 I always use ester oil in the changeover.

Yes the airconditioning.com site is a great one, and there are other similar good sites. Be warned you will see differing opinions, this stuff is not always an exact science.

For what it is worth, I recommend against any refrigerant that is neither pure R-12 or pure R-134. The mixes create a host of problems if you ever take your car into a shop to work on the AC after you've fiddled with alternate refrigerants. There are really smart folks who will disagree with me. For me, I stay with the straight stuff. And like I said before, if I encounter a system with a blend in it, I WILL NOT WORK ON IT. I am not alone.

V-8, and others, if you have not invested the 75 bucks or so (or less) a good gauge set costs, do it, E-bay has em all the time. They are worth their weight in gold if you are working on AC. The gizmos and gadgets I have are nice, but the gauge set is primary. As you will notice on some websites where they dispense free advice from really good folks, they always want to know 4 things... ambient air, hi side pressure, lo side pressure and vent temp. You need a gauge set for 2 of those. Oh and as a postscript... I bought several digital readout thermometers from Harbor frieght... I live and die by those guys. ANd they are under $10! Great in the vents.

Happy Exploring


Chris

Happy Exploring

 

[V8BoatBuilder]

Gauges were the very first thing I ever bought, got a decent deal at Autozone. I wouldn't even think of doing anything without them! It's pretty much impossible to do any kind of AC work without them. I also have a thermometer probe for my Mac Multimeter - an invaluable tool.

 

[Bennett Lewison]

30 DOLLAR KITS

I must be one of the lucky ones! Three years ago i took my 93 Ranger to the shop for AC recharge. I was informed there was a bad leak in the condenser. The repair cost was going to be close to $600.00. I went to Wally World and picked up a conversion kit and a can of R134 stop leak. That was three years ago, last week i added one half of one can of R134 to the system. The air coming out is very cold! Ben

 

[Glacier991]

Ben..

Don't misunderstand, I think that's great and hope it stays that way. Let me try and clarify a couple things. First let's examine the diagnosis and proposed charges. You did in all probability have a condensor leak, how bad is questionable. That meant you had zero refrigerant charge (a good thing as we will see in a minute). $600? well, a leaky condensor could be sent out for repair, slight savings, and if it leaked in one spot, another is likely soon behind. Not a good bet for a shop, and at the cost of R-12, not something you'd want a come back on. Cost of a new condensor ? $150 to $225 depending. Oh since the system was open, a new receiver dryer. Cost? $75 or so. Since you don't know what happened to your oil charge, a flush and total recharge would be wise. Cost of material ? $100 - $150. The rest would be labor. $600 was in the ballpark in other words. They were not trying to rip you off.

Now, I have some doubts about the size of your leak. Stop leak has a place, but think about it, if it could plug a BIG hole, why wouldn't it plug up the expansion valve, that hole in it ain't all THAT big. It apparently worked for you, and like I said that's great.

Some of the problems I see with the $30 kits are: if there is residual R-12 people add the kit in right on top of it, mixing refrigerants... a no no. If there is a charge, some simply vent it to the amosphere (a federal crime these a days and not good for the environment. - I'll bet the kit tells you to take your car to a shop have have them recover any remaining R-12 before adding the kit. YEAH right!) Next the oil. Auto air conditioners are like 2 cycle engines in that their lubrication is carried in another medium. Here in the refrigerant. R-12 systems use mineral oil. Mineral oil, is not, for all practical purposes soluable in R-134. So it won't carry it through the system for lubrication. PAG or Ester oil is soluable in 134, so that's what gets used. PAG and ester (POE) are not at all compatible. PAG and mineral are not either. POE and mineral coexist. Some think when you have ESTER added to a mineral oil system with 134 any excess mineral oil migrates to low points and sits. Me, I dunno, I spoze so. But how can you know the state of an oil charge when adding ester oil in a changeover kit? I wonder how they calculate these things into a one size fits all arrangement.

So you probably had the best possible scenario for a changeover kit, and met all the "one size fits all" designer's assumptions. I'm glad it worked and that you are happy. I see far too many that are not.

Happy Exploring

Chris

 

[Glacier991]

Ok.. one last comment here... based on a conversation I had with some buddies today. We were talking about this thread and about Ben's post in particular. Someone said to me "You aren't going to stop those who want to invest $30 bucks in a kit from doing so. They don't have working air to start with, if it works for a while great, if it trashes their system, they are not any worse off." And then ," You'd do better by telling them when and how to use those kits."

I gave it a lot of thought today, and I suppose there is some truth in what he said. So, with the initial warning that I do not endorse nor recommend these $30-$40 reftorfit kits, and in the vast majority of cases think you do more harm than good.... let me try and see if I can come up with some recommendations.

First. When is a kit NOT appropriate. Hmm, if you have a crumped compressor, do not replace just the compressor and add a kit. Usually a bad compressor will have contaminated a system beyond your imagination in its death throes. The only sure fix is to flush and replace whatever cannot be successfully flushed. Oh and if you EVER have a system open, always replace the receiver/dryer (or accumulator depending of the manufacturer and type of car - same thing more or less for our purposes). Another - you have a 93 and earlier system (or some 94's were also R-12). The cooling is there but low. DO NOT JUST ADD A KIT. (see below). I am sure there are other times a kit may not be appropriate, but that all I can think of at this instant. (bearing in mind I do not think a kit is EVER a really good idea)

NEXT... When might we try a kit. Ok... You have an otherwise semingly good system that gradually over time seems to blow warmer and warmer air until it stopped blowing cool air altogether. We can assume there is a slow leak and you lost your charge of R-12, or most of it.

Here's the rub here. R-134 molecules are significantly smaller than R-12. If you had an R-12 leak, imagine the leak rate with R-134. Can you fix leaks? sometimes. And sometimes the leak fixer stuff in cans might work (see Ben's post). Two most common leak areas ? Compressor seal (fixable but not for 99% of DIY'ers) or valve cores. The valve cores in an R-12 stem look like big bicycle tire schraders - and in fact they more or less are. Screw right in and out in the same fashion. A definite DIY job to replace these ASSUMING THERE IS NO REFRIGERANT CHARGE. Bad news about refrigerant (some call it freon, but that is a DuPont trade name so I try and call it refrigerant) if some squirts you in the eye, you WILL lose the cornea or sight in that eye. Goggles or suitable eye protection are a must while working on a system with any charge in it. "Well" you ask "How do I know if I have a charge? Can I hook up a simple gauge from the $40 kit and see ? Yes and no. The AC will not operate if the charge falls to a certain level. If the AC is not operating, and there is enough freon to saturate the system (not a lot needed for this) the pressure will be the same in a non operating low charged system as it would be with a full charge. Put another way if you put 6 oz of refrigerant in a closed 5 gallon container it would read the saturated pressure of the refrigerant(pretty close in PSI to degrees farenheit at normal temps, eg. 70 PSI at 70 degrees). If you filled it 3/4's full, it would read the same. So reading a partially charged system in a static or non operating state won't help you determine anything. If the charge is so low you cannot run the system, you KNOW you are really low, just not HOW low. NOW folks, understand venting R-12 into the atmosphere is against the law. The fine is extremely high. But I have seen some folks will try a little test, figuring a little vented to fix a system is better than refilling one and letting the entire charge bleed away. What these folks do is to use a little stick or small screwdriver and press down on the schrader valve for about 5 seconds and see if the hissing stays the same or starts to lessen- these same folks ALWAYS have eye protection when I have seen this. IF i the hissing stays the same there is probably a decent amount of refrigerant in the system. If is falls off, they stay with it and bled off what in all probability was a VERY slight remaining charge, until it is gone.
If the charge is a decent one (good steady hiss), it should be recovered by someone with the equipment o do this. I'll offer no other ideas or suggestions, PERIOD. Mind you I am not suggesting the former either, just telling you what I have seen in my long life.

So with your charge gone, either my leaking away to by being recovered, next what? Ok here is where I differ greatly with the kit idea. You spent $30-$40 on a kit. Have access to an air compressor? Buy one of those $15 Harbor Freight venturi air pumps. Buy a single r-12 hose with a shut off on one end. (another $15). Connect this to the valve on the high pressure side. .This is the smaller line running from the compressor to the condensor in front of the radiator - or maybe just after the condensor running back to the receiver/dryer again, it varies, the line will be the smaller, usually metal, ) Hook the other end to this venturi pump and hook up an air compressor. Run this as long as your compressor can stand it... 30 mins should be good. (relatively speaking). Add the changeover fitting to the other valve (the one on the bigger hose leading from the firewall of the car to the compressor or maybe on the receiver dryer AFTER the expansion valve - it varies. If it is on a line, the line will be the bigger of the two. ) do this while the vacuum pump is running). When you have run the pump as long as you can or at least 30 mins if able close the valve on the hose and shut off the pump (shut off the air compressor in other words) connect the 1st can up from the kit and let it run into the low side UPSIDE DOWN. (I know I said NEVER, but the kit ONLY has a low pressure fitting, and if the system is not running this is safe. NEVER DO THIS ON AN OPERATING SYSTEM, EVER EVER EVER!!) It should take the entire can. Let it sit a few minutes to equalize in the system - eg. vaporize past the expansion valve until the pressure is equal on both the high and low sides of the system. Quickly unscrew the hose from the high side fitting. There should be adequate system pressure there now to keep air from leaking in, in fact some refrigerant may leak out as you unscrew it, that's ok.

Next, start the car and see if the AC will operate on this level of charge. If it does, the rest of the rerigerant goes in on the low pressure side, can RIGHT SIDE UP. A can or pan of hot water to float the can in as the refrigerants is fed into the system helps speed the process. More or less follow the kit directions at this point.

That's the best advice I can give. I don't believe in the kits. I do not recommend them, but if you absolutely have to use one, maybe this will help.

Happy Exploring

Chris

 

[V8BoatBuilder]

Chris' advice is top notch, but I feel slightly different on the kits. I think with the addition of a venturi vacuum pump and a real manifold gauge set, A/C conversions can be done sucessfully for about $100 + evac. The manufacturers really should sell kits complete with a manifold and pump, or at least tell people.

The low-pressure only gauges that you can buy are worthless. Also, not having a manifold makes the A/C work extremely difficult. If you want to do the conversion, use a kit. It will be a great chance to learn about another system in the truck and most likely save some money. Thank god A/C can be done by the DIYer, and I give props to companies like Interdynamics for giving us that ability.

 

[Glacier991]

Evening V8.... I think with your post we may have finally come full circle here. I think I started with the idea that AC COULD be DIY, and linked to a post on it. I was just unfavorable on the "kit" approach. If someone wants to do their OWN AC they can... like you however they really kind of need a gauge set to start out properly. In some localities rental places will rent a vacuum pump. For a cash outlay of under $125 you can have most of what you need, (save the pump for evac) to flush, evacuate and repair your own. As you accurately point out the little low pressure vacuum gauge with the kits is all but worthless. My point was that you may need to do more than the simple kit explains to you, not that it could only be done by a pro.

We all come to this site to learn how to do our own work. Some are adventurous and capable, others just want to see what they MIGHT be able to handle. Between us we've covered that ground...So see, we don't disagree all that much, and we've both added to the collective knowledge here. Thanks !


Happy Exploring...

Chris