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Air Conditioner Queries

Air Conditioner Queries

Moburg, Shield, Lee, Stanford, Stern, & Bristow

Mark Moburg

JHS wrote:

I decided to try for Max. cold air from the A/C. I removed the vaccum line from the water valve. The lever on the valve moved to the very top of the left side. I assume this has shut of the water 100%. My question is this. Does anybody know if, by doing this, can it damage to the system ? I will return the line this fall when I will again need heat.

Shouldn't damage the system, but I just checked Kirby's book and the factory manual, and the "no vacuum" gives full heat. To quote the factory manual, "The water valve is closed as vacuum is applied and no water flows through the heater matrix. When heat is selected (either low or high) the vacuum feed is removed and the water valve is opened to allow water to flow through the heater matrix."

It makes sense, if you look at the table in Kirby's book, when there is no vacuum to the water valve, lower flap, screen flap, or center dash flap, you end up with full defrost. In other words, in case of a complete failure of the vacuum system, you get defrost. A pretty good idea safety-wise.

David Shield adds:

I've done the same thing, I think there's no potential for harm. My A/C is a little weak and, like you, I wanted the maximum possible cold air. I plugged the vacuum line with a golf tee.

Larry Lee

Bill Shaw wrote:

While cruising along one day my air conditioner suddenly cut out. Stopped blowing and cooling. After replacing the fuse located on the passenger side, blower motor and switch began working again but not AC. Pulled down the passenger side panel and put a new fuse in the in-line fuse for the compressor. (At least I think it is for the compressor) Had the wife turn on the blower for AC while I looked at the compressor clutch. Clutch engaged for a split second -- It did turn -- and immediately blew in-line fuse.

That is the extent of this jag lovers knowledge as far as AC goes. I then took the car to the local imports repair shop. He did exactly as I did and encountered the same results. His diagnosis: Compressor is shot and needs to be replaced. At this point I have to take his word for it. He is quite knowledgeable on imports, including JAGS. However I am still leery of the diagnosis. Price quoted to fix is $575.00 total. $345.00 for a NEW compressor, not rebuilt. I plan on maintaining this vehicle in top condition so I would go with the new as opposed to re-built. My questions to this, what I consider very knowledgable group, are:

  1. Am I fairly safe in accepting his diagnosis to this problem??
  2. Is the price quote reasonable?
  3. I can turn the clutch by hand. A little hard but it can be turned. I was always under the impression when the clutch 'freezes' it will not turn at all. Is this correct??

I have owned this car for a little over a year and when I first purchased it (from a dealer) the air conditioner was quite noisy. Took it back and they supposedly rebuilt the compressor and installed a new clutch? I would think it would last more than a year. I am sure that if I contacted the dealer I would be told the warrenty is void after one year. By the way it was purchased from a JAG Dealership.

Any feedback from this group would be greatly appreciated. Thanks in advance.

You may have two separate problems here, but you may only have one real one. As has been noted here recently, Harrison (GM) A-6 compressors tend to be noisy. Your mechanic may be trying to pull one on you, or he may not know much about these compressors. I have no idea whether it really needs to be replaced, so I'll ask how it was cooling before the clutch fuse problem. If the cooling performance was good and the noise is not so loud that it sounds like the poor thing will self-destruct in five seconds, it's probably okay for a while. Even if you do need a compressor, get a good rebuilt one for around $100-125. "New" doesn't buy you much here.

Now for the clutch. All this thing is is an electro-magnet that pulls one disc against another to transmit rotary motion from the pulley to the compressor shaft. When it causes fuses to blow -- assuming there is no other wiring problem -- it's because the magnet coil has a short to ground. A faulty compressor can not cause this. The only fix is to change the clutch, which can be done without changing the compressor or opening up the refrigerant system. (If you do have to change a compressor, change the clutch too.) Clutches can also fail mechanically, but that doesn't seem to be your problem. That doesn't cause fuses to blow unless excessive slippage causes everything to overheat to the point where magnet-wire insulation fails.

Here's a quick test. With the ignition switch in RUN, but without starting the engine, have someone turn the A/C on while you watch the clutch. The clutch should audibly click on and stay on until the A/C is turned off, at which point the clutch should audibly click off. If it immediately clicks back off and/or blows its fuse when the A/C is turned on, it's probably shorted. You may also want to disconnect the clutch wire, turn the A/C on, and see if the fuse blows. If so, you have a short somewhere in the control circuit.

Hope this helps. Feel free to inquire further, if need be.

Michael Stanford on Conversion to R134a

Converting to R-134 is easy, just requires a few tools, a bit of reliable information and some time. Unfortunately, I was unable to get reliable information from the three local AC shops I talked to, so I became educated, took the EPA test and bought the tools myself. FYI, right now in the US, R-134 can be purchased off-the-shelf without EPA certification.

It hasn't been really hot since I did the conversion, possibly only 90-92, so the verdict is still out. One thing about R-134 is that it requires higher condensor effeciency to work well. On the Jags the original serpentine condensor is not a very effecient design and can hamper the liquid converson of the refrigerant. My car has an aftermarket condensor installed (a 4 path serpentine unit, still not the best) which is a good bit more efficient than the original. I also have a primary electric cooling fan system, so I am not a good "benchmark" to compare.

You can see my installation at

Do take the time to browse around it is a fantastic site with a great deal or information about auto AC systems and conversion.

There are other alternatives to R-134 which work very well, are cheap and don't require oil changes. Those alternatives are the zoetropic blends, such as Autofrost, Frigc FR-12, R-406 and some others. They are great refrigerants however, since they are blends, if you have a leak you must evacuate and replace the entire charge. It is also difficult to find shops to service zoetropics other than FR-12, which is handled in the US by Jiffy-Lube. I take some comfort in knowing that the first blended refrigerants were patented by George Goble, a guy who lights his grill with liquid oxygen.

So, I suppose that if you are doing the work yourself and have access to a vacuum pump, manifold gauges and whatnot, a blend is a good alternative. Otherwise, use the original R-12 (about $50 a pound now) or convert to R-134 ($5 for a 12 OZ can).

BTW, you can get your own EPA certification to buy your own refrigerant by taking a small exam at


More from Michael Stanford

Many of you have seen my posts on AC systems, so you know my history.

I can tell you for sure that any AC shop that tells you that R-134 conversions won't work or can't be done, should not be patronized. They just don't want to go through the conversion process because it is not profitable and anytime older AC systems are worked on additional problems crop up. Especially on Jaguars.

AC is a simple system and there is no real mystery there. The R-134 switch just requires a lubricant change to be reliable and the reduction in cooling efficency is only a few percent. Most Jag owners who take the time to keep the evaporator clean and keep the flaps adjusted in the climate control won't notice any difference.

Good practice: always replace the filter/dryer when changing refrigerants. PAG or Ester oil is suitable, however the PAG is chemically more compatible with the refrigerant. Just get as much of the mineral oil out of the system prior to charging. GM recommends PAG oil and they cover PAG charged retrofits under warranty on millions of cars.

Oh, and by the way, I converted my Jaguar to R-134 a week or two ago after running a blend for the past year. I made the change to R-134 simply due to cost and availability of the refrigerant, and the fact that the blends are more difficult to aquire. It is in the mid 90's here today and during the 350+ miles I have driven this weekend, I can honestly say that the AC cools just fine.

Daniel Stern's Opinion on Conversion to R134a

Licensed s.609 Automotive A/C Technician

E-code headlamps, fender repeaters, etc.

There is a lot of misinformation (and intentional disinformation) flushing through the car hobby and repair industry about the state of auto A/C in 1997. We see people rushing to convert their perfectly good R12 systems to R134a, we see people demanding R134a systems for new installations, and we see charlatans pushing ineffective, dangerous, and/or nonapproved refrigerants and repair techniques. Worse yet, we see even bigger charlatans claiming that R134a is almost magical in its ability to go into any system, cool as well as R12, never create any combatibility problems, insulate your house, filter your coffee, and get your clothes whiter, brighter, longer. (Well, okay, maybe not those last three, but you get the point. R134a is being passed off as some kind of magic bullet for A/C systems.) The fact is that 134a, while it is nearly universally used in North America and many other countries as the OE refrigerant in '93 and newer cars, has numerous significant disadvantages over other refrigerants.

It is not a good idea to convert your R12 car to R134a or any of the R134a-based refrigerants (FRIGC and Freeze-12 come to mind). They are, relatively speaking, extremely inefficient refrigerants. Also, they are HIGHLY incompatible with R12-type oil. They operate at radically different pressures, so calibration of R12 expansion valves won't be optimal. Also, since 134a is so inefficient, one must use larger compressors, condensors, and evaporators to get the same level of cooling as from an R12 system. This is difficult and expensive to do on an existing system, so you get much less cooling with 134a. Perhaps most troubling is that R134a, unlike most other refrigerants, is not chemically inert. It is reactive, and has been shown to cause reproductive damage and is a suspected carcinogen.

Now that I have detailed some of the disadvantages of converting, let me outline what you would need to do to convert to 134a so as not to shell any of the components.

You're going to need:

  • Barrier-style hoses (The R12 hoses are permeable to the smaller R134a molecule)
  • All new seals and O-rings (ditto above)
  • A rebuild or thorough flush of your compressor. Which one you will need depends on the design of the compressor. Early Chrysler, York and Tecumseh compressors, for instance, use an oil sump and pump which cannot be "flushed" of oil like non-sump type designs, and because 134a is so violently incompatible with 12-type oil, you have to get ALL of the old oil out.)
  • New receiver-dryer with XH7 or XH9 desiccant

In addition, you're going to want to purchase a new condenser of the "manifold" or "parallel-flow" design to try to get as much condensing surface as possible for the refrigerant. The inefficient 134a, under high-demand situations, must literally be *forced* to condense. The serpentine condensers used in R12 systems do not have this capability. People often cite low cost of the R134a refrigerant itself as a reason for converting. Have a look at that list above and it becomes readily apparent that $80 worth of R12 vs. $20 worth of R134a is an irrelevant comparison.

There are other legal, safe, effective and efficient options if you have decided, for whatever which reason, to convert your system to a non-12 refrigerant (more on this later). Various companies have brought various refrigerants to market. Many of them have been minimally tested, have disadvantages similar to 134a, and/or other deployment difficulties. For instance, a lot of the new refrigerants have a very difficult time carrying any kind of oil back to the compressor. R12 has very good oil carrying capability, so the vast majority of existing compressor designs are meant for use with a refrigerant that will bring the oil back and lubricate the compressor. New oils have been developed to work reasonably well with the new refrigerants, but industry data confirm that compressor failure rates are up since the advent of refrigerants that don't carry oil as readily.

My own research and testing has turned up two very interesting refrigerants that seem to work extremely well, with minimal deployment difficulties. Those are R406a, and GHG-X4. Both refrigerants were invented by a Professor George Goble of Purdue University in Indiana. I don't work for the company, I don't sell the stuff, I have no association with Mr. Goble or anyone else on his refrigerant staff, except I've communicated with them by e-mail a few times. I point this out to indicate that I'm not trying to sell something, don't have any particular agenda or ulterior motive, etc.

Here is a rundown of some of the advantages of these two products as conversion refrigerants (actually, EPA's preferred term is "substitute" or "replacement" refrigerants.)

  • They are MORE efficient than 12, yet they operate at similar pressures, so the expansion valve calibration will remain optimal and your existing condenser and evaporator will function MORE than adequately. (improvement is usually quite quantifiable with a good A/C thermometer in the center outlet. Air outlet temps are usually 2 to 12 degrees colder than with 12.)
  • They are completely compatible with R12 type oil, so no system flush or compressor rebuild.
  • Both 406a and X4 have passed all UL, DOT, EPA and ASHRAE tests for safety and utility in mobile and non-mobile systems. They are certified nonflammable.

Are there any disadvantages? Yes, and here they are:

  • It is a ternary zeotrope, which means it is made of three components. This is an advantage AND a disadvantage: Leaking systems theoretically must be completely evacuated and recharged. Also, charging must be done in a LIQUID CHARGE fashion. (Note, this also explains the improved efficiency. The three factions boil/condense at slightly different temperatures. This is known as a temperature "glide" and effectively increases the usable condenser/evaporator area, creating the increase in efficiency.)
  • You still need barrier hoses, because R12 type hoses are permeable to the smaller R406a factions' molecules.
  • Ditto new seals.
  • New fittings and system labels are still legally required, since EPA has determined that each individual refrigerant product must have its own set of uniquely-threaded fittings. Adaptors and replacement fittings are available. (Note, this is a legal requirement. Physically and chemically, these two Rs are completely miscible and compatible with R12.)
  • Shops using R406a and X4 may be more difficult to find than those using 134a. Production and distribution of 406a and X4 has been ramping up steadily for the past several years.

Now I have to ask YOU a question: Why are you converting to anything or demanding a non-12 refrigerant? R12 is still around, you know, and anyone who tells you otherwise is lying or ill-informed. There is plenty of it in the US. There is MORE than plenty of it in the US. And there will be for a very long time. The best policy if you've a working R12 system is to keep it an R12 system.

Some will tell you that R134a is the only legal refrigerant. That's wrong. Go to the EPA SNAP (Significant New Alternatives Plan) homepage and see for yourself that many new refriferants, including 406a and GHG-X4 have passed all the safety tests, are certified nonflammable/noncorrosive, etc.

Some will tell you that 134a "moves more heat" than R12. That's also wrong. Some will tell you that no flush, rebuild, or anything else is needed when converting to 134a, and that you can just drop 134a into an existing system. For most systems, That's dangerously wrong. Information on conversions and refrigerant alternatives can be found at George Goble's e-mail (he's happy to answer questions) is

Converting a Series III Air-conditioner to R134a by Mark Bristow

In servicing my recently acquired 1982 Series III XJ6, I noticed the Air-conditioning compressor (GM Harrison A-6) was throwing oil thru the front seal (although it still worked great.) Hot weather coming on, I found a replacement at Western Auto (Parts America) for $59.95 with core exchange. A friend of mine is liscensed for R12 removal and has the equipment. He drained my system, and me and my dad went to work. We removed the compressor and replaced it with a remanufactured GM A-6 designed for the temperature/heat fuse. (Please note I had no leaks on the system.) We changed the accumulator/dryer-and changed only the o-rings we had disturbed. (Some techs say you must replace all the o-rings in the system and the expansion valve as well. The GM shop manual on the A-6 compressor said to replace ONLY those o-rings which were disturbed and expansion valve replacement was not necessary unless the previous compressior had failed-and my system was working well, even though it was running out of oil.) We then pulled a vacuum on the system down to 28.5 " of mercury for 45 minutes.

We added 8 oz of Ester oil to the new compressor. A tech at informed me the original R12 charge was 3.4 lbs (the original tag indicating the R12 charge was gone from my bonnet), so we first attempted an 80% charge which didn't cool very well, then a 90% charge which resulted in a vent temperature of 55 degrees farenheight on the road and 60 degrees farenheight at idle speed with an ambient temperature of 90 to 100 farenheight.

I then discovered a leak in my new system. We failed to be certain the charge valves were tight and the high-side valve was leaking. We discharged what little R134a was in the system, put in new valves and new quick connect R134a conversions and pulled a vacuum on the system to 28.5 " of mercury for 4 hours just to be sure there was no leak again. This time, with a thermometer in the vent, we began to charge the system. At 36 ounces, about 65% charge of the original 3.4 lbs (for the R12 system), the temperature in the vents reached 38 degrees farenheight with an ambient temperature of 90 - 90 degrees. On occasion the temperature in the vents goes down around 32 degrees farenheight. The R134a system has worked great for weeks now and it's Hot summer time in West Texas 90 to 100+ degree (farenheight) days. The system cools as good or better than the original R12 system did, and I am happy and cool. Total cost was about $225.00. (My friend donated the labor and equipment necessary for R12 removal in exchange for the R12 in the system.)

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