Is there anything about the A/C compressor on a 70 Valiant that would not allow me to retrofit to R134? I was told there is some valve built in the compressor that would not take the retro. The A/C worked great before I took it out to rebuild the engine. When I tried to pull a vacuum I have a leak aound the front compressor seal which would explain the oil that was present on the clutch before I removed it. Should I bite the bullet and have the seal replaced and the system charged with R12 or do I install the retro kit and use R134 with leak sealant? Cheaper is not always better.

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70 Valiant Super Six

I would have the seal replaced before reinstalling the A/C. That way no leaks! As far as going from R12 to R134 I did that on a 68 Valiant that I had. I had put a complete in the car and under the hood system in from a 75 Valiant. All I did was put in a new expansion valve and dryer (one for either R12 or R134), change the oil in the compressor with oil for R134 pull a vacuum and charge it with R134. That was using the Chrysler 2 cylinder compressor. Man that thing got cold. It would fog up the windows on the outside at night while stopped at a light. The other thing you could do instead of repairing the compressor you have is go with one of the newer compressors. They don't take as much power to run. I don't know about any valve in the back of the compressor as I didn't have to take anything out of the compressor to get it working other than changing oil. Oh you may want to set an electric fan in front to help push some air through the condenser while you are charging the A/C. That will keep the A/C from overheating while you are charging it.

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Former bent 6 owner
Mark

The "some kind of valve" you've heard about is the EPR valve, and it is not present in the A-body A/C systems until the 1974 model year. Your '70 already has the clutch-cycling switch system that will be utterly "transparent" to an R134a retrofit. The advice to install a new compressor shaft seal is an excellent one. Do NOT be tempted to install a "remanufactured" compressor; they are junk. However, DO install a parallel-flow condenser to get back the performance that will be lost due to R134a's lower efficiency compared to R12. As a bonus, installing the parallel-flow condenser will also reduce the head pressure on the compressor, which in turn will reduce the torque required to turn it.

False. This is one of those myths that just never seems to die. They take *MORE* torque to turn than the originals do, because of much higher internal friction (6 cylinders instead of two, PLUS the swash plate). The newer type compressors have a more even torque load which can eliminate the need to be quite so careful with bracket condition and belt tension to avoid engine shake at idle due to the early compressor's "peaky" torque loading, but the early compressor not only takes less torque to run, it also is much more suitable for an R134a retrofit, because unlike the newer compressors it has its own oil pump.

Is there enough cooling efficiency lost in conversion to 134 to warrant the use of 12? The difference is $50 per pound on a 2 lbs 14 oz. system.

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70 Valiant Super Six

From what I saw with the conversion I did there wasn't any loss of cooling from the A/C. One thing those cars were known for was cold A/C. R134 is readily available and very easy to come by not to mention much cheaper than R12. It cooled the car very well even with 100 degree heat and high humidity.

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Former bent 6 owner
Mark

My car is a 74 and I am thinking about converting to R-134a. If it does have the EPR valve then where is it at and what do I do with it. My compressor has been remanufactured, replaced by previous owner. Has a "remanufactured for General Motors" sticker on it. Is that weird or what.

What about the clutch cycling feature. I am pretty sure my car does'nt have it.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

The EPR valve is installed in the compressor. To remove it, you remove the suction fitting (two bolts at rear of compressor). You'll then be staring in at the EPR valve. Sometimes there's a retainer ring; remove it if you find it, then use a small pair of pliers to grasp the valve and pull it out. Use a new gasket when reinstalling the suction fitting.

Your '74 doesn't have a clutch cycling switch from the factory. You'll need to add one. It's not hard to do, and adjustable ones are available so you can dial them in to behave exactly as you want. I've got one of those on my truck; I'll provide the P/N and source info tomorrow from the office.

As far as the "does too!" "does not!" statements you're seeing on reduced cooling efficiency: it depends on how the system is configured. An unmodified R12 system with a cheap R134a conversion (suck out the R12, change the oil and a few O-rings, drop in the R134a) will usually show a noticeable performance drop, especially in high-demand situations (slow or no car speed/stuck in traffic or sitting at a red light on a hot day). Whether the loss of efficiency will be enough to bother you or not is a matter of personal opinion and also depends on demand placed on the system, which in turn is a function of ambient temperature and humidity, sealing of the passenger compartment, whether the windows are tinted, color the car is painted, etc. Of greater concern is the higher system pressures developed with R134a than with R12 under those same high-demand conditions.

A proper retrofit on a '60s-'70s Chrysler system will give good results and good system life if you do it properly. A half-baked retrofit (suck out the 12, dump in the 134a) is a poor idea if you're planning on keeping the car. Read this post for more info on how to do it "all the way correctly".

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

What happens if I forget to take out the valve.

What is the purpose of the clutch cycling feature.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

The EPR valve and the clutch cycling switch both have the same job: to regulate the temperature of the evaporator so that it does not go below 32°F. If it were to go below 32°F, ambient humidity that condenses on the cold evaporator would freeze, turning the evaporator into a big chunk of ice. This blocks most/all airflow through the evaporator, and you stop getting cold air out the vents.

As with all fluids, the pressure and temperature of refrigerant are related. You can control either by controlling the other. As pressure drops, temperature drops. As temperature rises, pressure rises.

The EPR (Evaporator Pressure Regulator) valve works by opening and closing in response to pressure in the suction line. When it senses low pressure, it moves towards the closed position to reduce refrigerant flow. When it senses high pressure, it moves towards the open position to increase refrigerant flow. The valve is not an "either open or closed" device; it works rather like the throttle valve in your carburetor; it has a range of positions from all the way open to all the way closed. The idea behind the use of an EPR valve (which is just Chrysler's name for a device known generically as an STV, suction throttling valve) was to eliminate the clutch cycling which some marketeers must've thought was objectionable to vehicle owners. In a system with the EPR valve, the compressor runs full time whenever the A/C or defog is on.

The problem with the EPR system is that it begins to close long before the evaporator freeze-up point is reached, which hurts system performance in those maximum-demand situations I keep talking about (even a crappy, minimal system will keep up with low-demand situations). And the problem with EPR valves in a 134a retrofit is that 134a operates at different pressures than 12, so the valve's calibration doesn't match the refrigerant being used, so system performance takes yet another hit.

A clutch-cycling switch is a thermostatic device that senses the temperature of the evaporator (or the evaporator end of the suction line). It uses a capillary tube filled with a gas that has a specific pressure/temperature curve. One end of the capillary tube is wedged between two rows of fins in the evaporator, pushed into a tunnel into the suction line, or wrapped several turns around the suction line. The other end of the capillary tube ends in a chamber with a flexible metal disc at one end. When the capillary tube gas gets DOWN to a certain temperature, the flexible metal disc contracts, and the spring-loaded switch contacts leaning against this disc trip (TICK!), opening the circuit to the compressor clutch. The compressor stops pumping refrigerant, but the blower fan continues to run, so air is still cooled and blown into the passenger compartment. This adds heat to the evaporator, which in turn causes the capillary tube to warm up. When the capillary tube gas gets UP to a certain temperature, the expansion of the gas pushes the flexible metal disc outward, which pushes the switch contacts together (SNAP!), the compressor clutch circuit is completed, the compressor pumps refrigerant, and the evaporator cools down.

The nice thing about a clutch cycling switch is that it IS an all-on/all-off device, so there's no performance reduction curve at the fringe of the evaporator frost-up point. Also, a CCS doesn't know or care what kind of refrigerant you're using, since its only input is temperature. And with an adjustable CCS, you can tweak the switch's behavior to suit your particular system in your particular car in your particular locale's weather conditions.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

What is the brand and part number of the CCS ?? Is it universal or application specific?

I'll provide the P/N and source info tomorrow from the office

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

At the risk of starting a heated discussion, I have used hydrocarbon based refrigerants as a replacement for R-12 on my old ranger pickup.
http://autorefrigerants.com/ worked really well for me. I have read that some experts consider it a fire hazard, but burning Freon isn't too good for you either. The best bet is to just not get into a situation where your car is on fire, and you are sitting inside, waiting for any refrigerant to catch on fire.

Greg

These are blends of isopropane and isobutane. They're sold under names like EnviroSafe, RedTek, DuraCool, HC-12a, OZ-12, MX-12a, ES-12a, HC-12a, "anything"-12a). They're inexpensive and widely touted as "drop ins", even though legally there is no such thing as a "drop in " replacement for R12.

Do these hydrocarbon blends work? Yeah, they work.

Is it safe? The sellers say yes (of course), but can't seem to provide enough supporting data, despite 15 years of trying, to pass the refrigerant
safety tests ALL refrigerants are required to pass before they're legally
approved. The sellers claim it's due to politics and Big Refrigerant Inc's
desire to own the market. EPA says Don't. MACS says Don't.

One argument commonly advanced for these refrigerants is "You carry 20 gallons of gasoline and you don't worry about that, so why worry about 2 pounds of hydrocarbons in your A/C system?" The answer is that the fuel system is specifically designed and tested to store, carry and transport flammable fluids. The A/C system isn't. What's more, our old Mopars don't have anywhere near the ventillation that newer cars with their through-flow air exchange systems have. In a newer car, a small leak of hydrocarbon refrigerants is not as likely to lead to a critical (BLAM!) accumulation of hydrocarbons in the passenger compartment. In an older car without through-flow (all A-bodies and most other '60s-'70s Mopars), the opportunity for accumulation is much greater.

And don't think you're not at risk 'cause you don't smoke in your car. There are lots of sparks happening all the time in and near the passenger compartment. Blower motor, all the dash switches, static electricity, etc. It only takes one.

Freon does not "burn". In fact, like other halons, it tends to extinguish whatever fire it encounters. Fire + Freon can produce a toxic gas (phosgene), however, injury or death from phosgene created by a fire in an A/C equipped vehicle is far less likely than injury or death from fire or explosion caused or aggravated by hydrocarbon refrigerants. Think about it: The antidote to toxic gas exposure is ventillation. That's easy to accomplish and you've got time to do so after the exposure. The only antidote to a hydrocarbon explosion is not being there when it happens. That's much harder to do since it involves predicting the future.

if you mouse around on the websites selling this stuff, you'll find them talking about "legal 2nd-generation drop-in" refrigerant. This is a bit of doublespeak. Here's how it works: It's illegal to replace R12 with hydrocarbon refrigerants, but it's not illegal to replace R134a with hydrocarbon refrigerants. A law against the latter was never written, 'cause there's no reason why anybody would ever replace R134a with hydrocarbons. Unfortunately, that legal omission is being treated as a loophole by those selling hydrocarbon refrigerants. The idea, they say, is to convert your system over to R134a (which is legal), then replace the R134a with hydrocarbons. Nudge nudge, wink wink, elbow in the ribs, and if you happen, wink wink, to forget the "change to R134a" step, wink wink, why, that would be awful. Wink wink. Just terrible. Wink wink.

As a final note, A/C shops have sniffers that detect what the system you bring them is charged with. When they detect a nonstandard refrigerant, they will either tell you to leave or start making the cash register ring Large. If they detect hydrocarbons, they will tell you very quickly to get the hell out of their shop.

Hydrocarbon refrigerants work but are a really, really, really bad idea in motor vehicles. It'd be a terrible shame to get killed, disfigured or maimed because you were too cheap to fix your A/C correctly.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan, I knew that you wouldn't like it!

Seriously, there are a few benefits to hydrocarbon refrigerants:

1. It is environmentally friendly, and does not cause ozone depletion. R-12 certainly does, R-134 does to a lesser extent, hydrocarbons do not.

2. Hydrocarbon refrigerant carries more heat than R-134. It is more efficient, and will cool a car better.

3. As far as the shops that service it, I couldn't tell you, as I had the equipment to evac a system myself. I can tell you that you can release HC refrigerants into the atmosphere, with no consequences, legal, ethical, or otherwise. If you are concerned about taking it to shop, vent it out, and they may not notice it at all. (I tend to think of most of the members here as "fix it myself" types, and not prone to taking their cars into a shop.)

That said, Dan's points are valid, and useful to think about. As always, Dan has put some thought into his postings, and I am glad to read them.

Greg