No argument here. It's just that this environmental friendliness comes at too high a cost of personal safety.
You can make R134a work just as well by simply increasing condenser capacity.
2/3 true. It is illegal to vent motor vehicle A/C systems to atmosphere, regardless of what they contain.

Thanks for your points, too.

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

A 74 what? Darts and Valiants had cycling-clutch systems, B, C, and E bodies had EPR systems.

The EPR valve mounts inside the suction port on the compressor. Here is a picture of the EPR valve being removed with a set of needle-nose pliers:

http://moparmusclemagazine.com/techarti ... _large.jpg

Assuming you actually have an EPR valve, you really need to remove it to convert to R-134a (in addition to flushing and all that other good stuff). But if you ONLY remove the valve without replacing its function, then the evaporator will ice up on low fan speeds in cool/damp weather. To avoid that, install a thermal compressor cycling clutch. You can get "universal" ones, and you can make them work by wrapping the capillary tube around the A/C suction line as close to the firewall as possible, and taping the wrapped tube down with insulating tape. The best way is to install the capillary inside the airbox downstream of the evaporator and before the heater core, but that's an involved installation.

Set the thermal cycling switch to disengage the compressor at about 35 degrees F and re-engage it at about 38-40 F, and it'll work fine.

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Actually, R-134a is not an ozone depleting chemical. It IS a "greenhouse gas", and so are hydrocarbons. That is a tie.

A properly converted R-134a system will blow all the 38-degree air on a 105 degree day that the blower can manage. So will a hydrocarbon system. What's the advantage of using the illegal, unserviceable refrigerant instead of the industry standard refrigerant that ANY shop will gladly deal with?
All well and good.... until you take that nice long road trip and have an A/C problem in Muleshoe, Texas. (actually, Muleshoe is full of farmers that are so mechanically inclined they could probably build you a new AC system from scrap aluminum so that may be a bad example. Lets say, "... a problem in Muleshoe Texas on Sunday Morning an hour before the game starts on TV."


Don't get me wrong, I'm not one of the safety-nazi types that thinks all car hoods should be welded shut so those maniacal gearheads can't make "unauthorized changes." If you carefully weigh all the options and for some reason think that HC refrigerants are a good idea, I'm not going to want the gummint to arrest you. But I think if you step back, take a deep breath, get your mind off trying to do something "quick and easy," and put yourself in the frame of mind that you are going to engineer a good, reliable, LONG-TERM conversion, you won't conclude that HCs are a good idea.

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A-bodies got EPR systems in '74 (clutch-cycling until '73).

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

I sit corrected.

Now on a philosphical note... WHY did Chrysler stick with EPR systems on the "bigger/fancier" cars, and use the much better-performing cycling-clutch system on the smaller cars?

And why did they go backward on the A-bodies in '74? Was it a NVH thing where they felt that keeping the compressor running all the time was less intrusive than feeling it cycle? If they'd asked me, I would have said "nevermind the cycling, I'll take the instantly cold air and super-fast cool-down . Thankyouverymuch."

Chrysler had the best engineering of any car company of the 50s thru early 70s, no question... but they did do a FEW things that really make me scratch my head.

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The EPR system gave better humidity control, over a broader ambiant temp range, then the clutch cycling system. But the clutch cycling system, is more fuel efficent. The variable displacement compressors on many newer vehicles, are the best of both worlds.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Sorry for the delay, all. Was a real busy day; I grabbed the catalogues on my way out of the office and now I finally have some time to post part numbers and descriptions.

There are lots of different clutch cycling switches available. Right now, I have a 35706 on my truck.
It is made by Ranco, which is an old and very well established name in temperature control devices (they made the heater control valves used on '60-'62 Valiants). It has one adjustment screw for the cut-in/cut-out point. The capillary tube is 24" long, which is a lot longer than I need for my application, but that's really not a problem.

35822 is similar, but with a slightly different bracket and a 19-1/2" capillary.

35823 is likewise similar, but with yet a slightly different bracket and a 19" capillary.

Before I went to the 35706, I went through two 35821 switches. This switch is made by someone other than Ranco, and has a 19" capillary. My original was made by Cutler-Hammer, and was working OK, except I manhandled the capillary tube and broke it. C-H are no longer in the temp control business. This switch has two adjustment screws, one for cut-in, one for cut-out temperature. Theoretically, these allow you to dial the switch behaviour in so it's exactly how you want it. In practice, it's tricky to get the two screws set to where the switch does what you want, and easy to mess up the cut-in and cut-out points. If you're willing to stick with it and adjust a little at a time, you can squeeze extra performance out of your system. I got tired of trying and went to the 35706 w/single screw.

35810 is also a Ranco product, but a totally different kind of thermoswitch; it's fully electronic and comes with all the parts needed to replace an electromechanical thermoswitch. No adjustment screw, and the only real advantage of the electronic switch is no "Tick!" when the switch opens or closes (yawn! I like to hear things working.). The sensor probe is very, very short, so this switch would need to be mounted on the evaporator box or in otherwise close proximity to the evaporator core.

Now, all the above switches are fixed-setpoint: No control over their open/close behaviour from the driver's seat. That's not really a problem on a blend-air system ('74-up A-body, for example) that mixes heated air with cooled air depending on where the cool/warm slider or dial is set. And these switches can be mounted and made to work most anywhere. The one on my truck is screwed to the firewall, and the capillary is pushed into a tunnel designed for the purpose, in the metal part of the suction line. Factory A-body systems have such a tunnel, but it's already occupied by the TXV's capillary, which really needs to be there. No matter, you simply wrap the switch capillary several turns around the metal part of the suction line and cover with some of that split-down-the-side foam pipe insulation you can buy at any hardware store, $1 for 6 feet.

There are also adjustable/thermostat-type clutch cycling switches. These are used in most all aftermarket systems, and in a lot of factory systems—including all pre-'73 A-body systems. When you slide the "TEMP" lever on one of these cars, you're adjusting the thermostat switch. With the switch in its "least cold" position, the compressor is engaged only for short periods and only when the evaporator gets considerably warmer than 32°F. With the switch in its "most cold" position, the compressor is engaged almost constantly, stopping only when the evaporator is about to frost up. This kind of adjustability gives added flexibility to the system.

It's hard to retrofit a remote cable-type control into a car that didn't originally have it, so if you want to retrofit an adjustable thermostat, you'd be looking at a knob-type unit installed either in or under the dash. Not a big deal to install one, really, you just have to pick one with a long enough capillary tube to reach the evaporator housing plus several inches (to install, you drill a hole in the evap housing and push the capillary tube in between two rows of evaporator fins, then seal the rest of the hole with whatever sealer (caulk, mastic, RTV) you happen to prefer.

Fortunately for retrofit artists, there's a wide variety of knob-type switches.

35820 is similar to the Ranco switches shown above, with the obvious addition of a rotary knob shaft (supply your own knob, Four Seasons 20980 or 20981). The capillary tube's 16" long, probably plenty for an A-body; not much distance between the dashboard face and the evaporator housing.

35715 , just about the same, but with a REALLY long 49" capillary.

35845 has a 34" long capillary.

35717: Similar, but with 2-bolt face mount (instead of screw thread face mount) and a 28" capillary.

There are more, and other brands, but this is quite a spread.

Thermal installation is as discussed above: Wrap the capillary around the metal part of the suction line closest to the evaporator, or push it between fins in the evaporator itself. Mechanical installation is easy: Mount the switch securely. Electrical installation is also easy: each of these switches has two terminals. The switch simply gets cut into the power feed to the A/C clutch. If you want your mode selector switch to live a long and happy life, do what the factory should've done (and in later years starting in the '80s, did): add a relay so the high current for the compressor clutch isn't gradually cooking your selector switch to death.

Now, go forth and cycle that clutch!

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

I'll admit, that is an advantage. Its a stretch, and it aint worth the loss of cool-down rate and total system capacity, but it IS indeed a legitimate advantage.

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