Retrofit your Air Conditioning System to R-134a

Chris 96 WS6  Mar 31 2006 - 5:40pm   

Background

Third generation F-body cars are anywhere from 8 to 17 years old now, and that usually means your air conditioning system is either wasted or is going south. It could be a number of things: bad compressor, a blown o-ring, or worse, the dreaded slow leak that no repair shop can find. So, you probably do what I've done for years, just get it charged up in the spring and hope it cools until fall. Well, that didn't work for me this year.

Well, if you haven't looked, R-12 (DuPont's name for R-12 is Freon) is more expensive than ever--I paid $35 a pound, and since it is no longer produced it will only get scarcer and more expensive. To boot, after the shop charged my system (for $130), it wouldn't run, turns out the compressor failed, too (and leaked out all of my $130 of R-12)! If you have a bad part, its actually cheaper to go ahead and convert the system rather than pay $35/lb. for R-12 (R-134a is $7/lb.).

I’d been wanting to convert to R-134a (Dupont's name for R-134a is Suva) refrigerant for years, due to the high cost and eventual unavailability of Freon. This was the perfect time, and it turned out that it was a lot easier than I had been led to believe.

If your system leaks all the R-12 out annually, even if all the components are working properly, it is financially worth your while to convert to R-134a, recharging will cost only $60 instead of $120. Maybe more importantly, all the stuff need to charge an R-134a system yourself is available to anyone (no license required as with R-12). If you have a broken component (most often the compressor), it is advantageous to go ahead and retrofit while you are opening up the system. If you're a/c works great and you don't have any leaks, don't worry about it-don't retrofit until it becomes worthwhile to you monetarily.

I got two estimates from a/c service shops (both nationally known chains), one for $500 and something for replacing the compressor, orifice tube, and accumulator (not including recharging with R-12), and another for $700 for replacing basically everything. With an R-12 recharge, I was looking at $650-800 to get cool again. After telling them I thought they were rip off artists, I decided to do the work myself. I searched the internet and "educated" myself about air conditioning systems.

If you are wary of working on you’re A/C system, read on. Even if you leave the charging to a shop, you can still do the repair work yourself with a substantial savings on both parts and labor. Working on an empty system is easier and simpler than you might think.

Two internet sites I found that that deal with conversions are: www.delanet.com/~pparish/cond.htm, and www.echocheck.com/maconair/pa00002.htm. These sites are run by accomplished a/c service shops and will give you a comprehensive overview of retrofits of R-12 systems to the new R-134a refrigerant that is readily available and cheap. I recommend you read through these sites before starting any conversion work.

The essence of the conversion is this: If you are currently running R-12, you have two options. First, you can simply evacuate the system, charge with R-134a and PAG oil, and run as is. The lubricant used with R-12 is mineral oil. Mineral oil will not mix with R-134a, and thus you must use PAG oil. The mineral oil does not need to be removed, as it will seek out quiet spots in the system to just sit there. This is actually the recommended OEM retrofit procedure from automobile manufacturers. The second option is to have the system flushed, removing all traces of mineral oil. In this case, you use ester oil (I don't know why, that’s just what is recommended). If you do not flush the system and use ester oil, it will mix with the mineral oil and "spark" in the system, not lubricating the compressor (which will lead to failure).

I have been told that all hoses must be replaced as well, but this is not always the case. As it turns out, R-134a has a smaller molecular structure, and can seep out through older hoses. If your hoses are in bad shape, you might think about replacement, otherwise its not recommended as necessary. If it leaks out, it will be slowly, and an R-134a recharge is so cheap it’s not a big deal.

Supplies

What you will need: Retrofit Kit (two 12oz. cans R-134a, one can 8oz. PAG oil/ 4oz. R-134a, adapter hose, new R-134a service port adapters, retrofit label, new schrader valves), a third 12 oz. can of R-134a (for a grand total of 40oz.), a large bore schrader valve and valve removal tool, Snap ring pliers (if replacing the compressor), safety goggles and maybe gloves, and a normal assortment of metric and standard wrenches/sockets.

I also recommend sitting down with a Chilton’s Manual and learning the parts to your A/C system, especially the high-pressure and low-pressure sides, and the locations of the high-side and low-side service ports.

R-134a Pressures Vs. R-12 Pressures: Use different amounts

One key to the use of R-134a is the amount to use. At a given temperature, R-134a will have a higher pressure than R-12. Therefore, you must use LESS R-134a in your system than you would R-12. The formula is this:

   R-12 amount x 90% - 1/4 lb. = R-134a amount.

In the F-body system, 48 ounces of R-12 are used (3 pounds). Thus, applied to the formula:

   48 x .9 - .25lb (.25lb is 4 oz.) = 39.2 ounces of R-134a.

Obviously, if you are doing this yourself, 39.2 is an unrealistic number. I put in 40 ounces, which was easy because of the retrofit kit and the typical 12 oz. cans.

The Retrofit Kit

I purchased a Johnsen's retrofit kit from Pep Boys, but any good parts store should have a similar kit. The best part about Pep Boys was that all the a/c stuff is on the shelf, so you don't have to have some hilljack parts guy try to help you. The kit contained a hose for charging the system, service port adapters and valve cores, a retrofit label, one can of PAG oil (8 oz. Oil, 4oz. R-134a), and two 12 ounce cans of R-134a. You will need an additional can of R-134a to make 40 ounces. Manifolds are available with high- and low-side pressure gauges, but I don't think they are necessary. If you are charging a dry system, the 3 cans of R-134a and one can PAG/R-134a is exactly enough, so as long as you empty it all in, you know the pressure is correct.

Replacement of Parts

No special tools are needed to do the job, even if changing parts. A new accumulator (the canister looking thing, also called a receiver/dryer) is recommended when converting, so I put one in along with a new compressor. Also, a new orifice tube is recommended any time the compressor is changed. This tube is a filter that keeps debris from circulating in the system (if the orifice tube contains lots of debris, I strongly recommend having the system flushed after all repairs are completed). The accumulator needs to have XH-7 or XH-9 desiccant in it to be compatible with R-134a. Luckily, the majority of off-the-shelf parts are designed to go either way (back to R-12 or convert to R-134a), so this was not a problem. Actually, my stock accumulator had XH-7, so it would have worked. But considering the age of my '88 IROC-Z, the desiccant was probably not removing moisture from the system very efficiently, so I replaced it. Replacement compressors also typically come dry, with no oil-making conversions easier.

Replacing parts is helpful to the conversion because it removes mineral oil from the system. It is important to stress that removing it is not necessary, but every bit you can get out helps. When a system looses charge, it also looses the oil, because the refrigerant carries the oil with it--there will, however, always be some liquid oil left over.

I’m not going to go into the specifics of actually changing out parts, that’s what the Chilton’s Manual is for (remember, always disconnect that negative battery cable first!). However, I'll tell you that it was far simpler that I ever thought, and the whole process only took me about 4 hours, including breaks.

If you are going to do the work yourself, have the system evacuated completely if it is not already totally empty. There's no sense venting 3 pounds of Freon into the atmosphere-its illegal, dangerous, and supposedly not good for the ozone layer. Once the system is zero pressure (actually atmospheric pressure), its easy to work on. Be sure to lubricate any new seals (it’s a good idea to grab a non-pressurized can of mineral oil to coat the new seals, because PAG oil is mildly corrosive to rubber). DO NOT get PAG oil on paint, its like brake fluid and will take paint off. (I did not learn this the hard way, luckily!).

When replacing the compressor, keep some things in mind. Many 3rd gen cars will have a pressure switch located on the back of the compressor which turns on the primary fan when head pressure reaches a certain point (see Willie's "Total Fan Control" Tech Article). This switch is NOT supplied with a new compressor, and must be transferred to it. You will need snap ring pliers to get the thing out. Once the snap ring is out, simply pull it straight out (it might require some wiggling, but its not threaded in or anything).

Second, drain out the oil from the old compressor, and add approximately the same amount of PAG oil to the new compressor. This is important to prevent burning up the compressor. The PAG oil charge supplied in the retrofit kit actually contains sufficient oil for the whole system, but It is my opinion that its better not to run the compressor dry, even if for only a few moments. Only add at most a couple of ounces of PAG to the compressor, too much can be as bad as not enough! Once the compressor is installed and the lines are attached, use a socket to turn the clutch hub clockwise about 15 revolutions. This will properly lubricate the compressor. You don't want too much oil in there, though, as this is bad too-just use good judgment.

Converting the Service Ports

Before charging the system, you must install the new service port adapters supplied with the kit. By law, every kind of refrigerant must have different kinds of ports to prevent mixing of different types. The new R-134a ports in the kit simply screw onto the R-12 ports. There is a low side port (with a blue cap) for the adapter located on the accumulator. This is the ONLY port you should charge the system with. The kit supplies two kinds of high side ports (with red caps) (high-pressure port is located on a line just in front of the orifice tube fitting), only one of which will fit our cars.

The instructions to the kit instruct you to remove the schrader valves from the two ports and install them in the new port adapters. The Low-side valve is just like a tire valve, and a typical core tool will work. The valve in the high side port is of larger diameter and requires the larger size valve core tool. If you use the normal sized tool, you will destroy the spring (like I did). I found the proper tool, along with a new large-bore valve core, at Advance Auto Parts.

The instructions recommend that the new service ports be installed with thread locking compound (they are not intended to be removed). BUT, I didn't. I simply tightened down the ports until they were very snug.

Charging the system

I must recommend at this point that you leave the charging to a service shop. Although many people have successfully charged their systems at home, there are a couple of things you can have done at a shop that will extend the life of the A/C system and its components. First, if replacing the compressor, pay close attention to the old orifice tube. If there is a lot of debris in the screen, the system needs to be flushed to remove any additional contaminates, as they will destroy your new compressor. Expect to pay around $100 for a flush.

Second. Before charging a retrofitted system, it is preferable to have a shop pull a vacuum on the system to boil out any moisture and air remaining in the lines. The standard is 29in/hg for 30-45 minutes. With a moisture free system, the components will last longer and perform better.

Charging it yourself

If you are not willing, for whatever reason, to have a service shop charge the system, I've included those instructions anyway. I actually did it both ways…charged it myself and the compressor went out after two months, so the second time I left the charging to the pros.

I will assume that you are ready to start charging the system and are doing so according to the instructions supplied in the retrofit kit. Start with the PAG charge, screw it into the charge hose supplied with the kit. Next, attach the other end of the hose to the low-side service port (with the new adapter on it). Tighten the wing-nut on the can-side of the hose all the way down, then back it out all the way. You will hear the slight rushing sound of the contents moving into the system. Hold the can upside down and above the service port. To remove, close the wing nut on the can first, then disconnect the other end of the hose from the port. Then slowly open the wing-nut again to relieve any left-over pressure in the can.

I recommend starting the engine and running the compressor to draw the contents of each can completely into the system. You will have to remove the plug to the clutch cycling switch (located on the accumulator) and jump the connections to allow the compressor to run. Do not run it too long, though, as it will burn the compressor up when low on oil and refrigerant.

Final Recommendations

The last thing you will need to do is adjust the clutch cycling switch. Located on the accumulator, the switch serves two functions: 1) it cycles the compressor on and off to prevent freeze up during use, and 2) it prevents the compressor from running if the pressure is too low. The switch needs to be set at 21 to 22 psi, to compensate for pressure differences of R-134a. The adjustment screw is located in between the two terminals on the end of the switch. It is typically set at 24-25psi with r-12, so ¼ turn of the switch counterclockwise should be -4 psi (1/4 turn = 4 psi).

The whole job was fairly simple. Total cost, including new compressor, orifice tube, and accumulator was under $280. Actually, I had a service shop price those three parts at $260, $18.99, and $79.00 each. I got them at Autozone for $130 (+$10 core), $1.99 !!, and $43.00. Talk about mark-up!!! The retrofit kit was $40, and the extra can of R-134a was $7. Other miscellaneous parts were about $15. I also saved about $150 or so in labor.

This article was updated on September 7, 1999 by Chris Renner with technical input provided by Bernard Tripp (aka GMTech).

 
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