A/c Expansion Valve...

[Mitch Leland]

Howdy,

I'm starting an A/C upgrade to my car. I've got a Rennaire Evaporator and ProCooler from our host, but it came with an R134 expansion valve, I want to continue to run R12. My local parts house guy said there's no difference in the valves. Since the new valve is marker R134 I'm wondering if that is true? I'd like to move ahead with the installation, but I don't want to do the work twice. Doing it once is bad enough...

Thanks,

[glennspiegler]

Whether u use R12 or 134, need to replace receiver/dryer. Are you doing the hoses? Upgrading to a rotary compressor? I want to do my whole system, but R12 is expensive and hard to find. Why not switch to 134. With the above changes would hope vent temp is less than 50 which is what now with old system. Also saw an additional condenser and fan for the rear left fender at Zim's, need to ask more to see if it is helpful. Sorry, I dont know the answer to your question, just have a bunch more. Glenn

[Jim727]

The ProCooler is a great addition and is also the receiver/dryer. I think the expansion valves are different for R-12 and 134, and not sure about the ProCooler, but why not ask RennAire directly? info@rennaire.com - they're very helpful.

As I recall, you no not want to mix refrigerants, so sticking with 12 is a good idea. +1 on Glenn's recommendation of a rotary compressor.

Jim

[khamul02]

Not sure about the x valve but rennaire are more than helpfull. Make sure to pull a vacuum for as long as you can. If I were you I would go ahead and replace all of the hoses as well.

[rusnak]

Hi Mitch:

I just found this:

http://www.mercedesshop.com/shopforum/showthread.php?t=93429

It says for MBs the R12 expansion valve is not even available anymore.

[Jim727]

I'll second what Tom said. If you have the old red hoses they absolutely need to be replaced. Not all that expensive, just a bit of work but the payoff is that you will actually get to keep that expensive refrigerant in the system where it belongs.

[Mitch Leland]

Glen,

I have a cheap (free) source for the R12, plus I think it will give me a few more degrees of cold temp and that's what this is all about. My hoses are good, so if I have to add a can every two years to top it off so be it for now. However I think I will replace the suction line that you have to move from the passenger side to the drivers side and add the 12" furnished piece before connecting to the ProCooler. There's an elbo on the suction line that doesn't nest very well into the wheel well and other hoses so I think the single hose might be a better bet.

I called Rennaire and I guess they were out and didn't return my call. I was trying to get the evaporator back in the car this weekend. Oh well there's always something else to do...

I know that I've read or heard that the orifice is supposedly different between the R12 and R134? Here's a link that Russ (rusnak) sent me:

Original expansion valves were R-12. MB does not sell R-12 expansion valves anymore, I am not sure of the after market suppliers. Its ok to use R-134a expansion valves with R-12 its just that the R-134a parts flow more. You may very well have R-12 in that system if the original fittings are still on the car. There are testers that can determine what kind of refrigerant you have, but I don't have much info about them.

[Mitch Leland]

Glen,

I have a cheap (free) source for the R12, plus I think it will give me a few more degrees of cold temp and that's what this is all about. My hoses are good, so if I have to add a can every two years to top it off so be it for now. However I think I will replace the suction line that you have to move from the passenger side to the drivers side and add the 12" furnished piece before connecting to the ProCooler. There's an elbo on the suction line that doesn't nest very well into the wheel well and other hoses so I think the single hose might be a better bet.

I called Rennaire and I guess they were out and didn't return my call. I was trying to get the evaporator back in the car this weekend. Oh well there's always something else to do...

I know that I've read or heard that the orifice is supposedly different between the R12 and R134? Here's a link that Russ (rusnak) sent me:

Original expansion valves were R-12. MB does not sell R-12 expansion valves anymore, I am not sure of the after market suppliers. Its ok to use R-134a expansion valves with R-12 its just that the R-134a parts flow more. You may very well have R-12 in that system if the original fittings are still on the car. There are testers that can determine what kind of refrigerant you have, but I don't have much info about them.

[billybek]

The TX (thermostatic expansion) valve is king in the refrigeration circuit. What ever it is designated to run is what it should run. There are differences in the refrigerants operating pressures and flow rates.
It may be possible, OTOH to run, especially with such a long suction line back to the compressor to ensure that "dry gas" (superheated, but not too much) is being compressed.
Usually valves are set at the factory for a given refrigerant to provide the proper super heat. How easy is it to make adjustments at the stem of the TX valve, or are they even adjustable (some of them are not)?
Good luck and let us know how it turns out....

[rusnak]

Mitch, I just went outside to look at my Procooler install. It is pretty ugly with all of the hoses bunched in the corner of the front fender well. I think I had a problem with the elbow, and wondered why they made it with a 90d bend. I did some straightening and adjusting. I don't know if this will crack your paint later, but I did struggle some with the fitment. I ended up with more zip ties on the hoses than I would be proud of, but then I'm not that proud to start with, haha.

On the other hand, I don't even think about it now, and the ProCooler works great. You get some condensation on the outside of the body.

[Mitch Leland]

Bill,

It looks like the TEV is preset without any adjustments. On Monday I'll see if I can chase down Rennaire to discuss the question. I also have some support people in town that I can talk with. I'm sure you're right, the density of the material has something to do with the flow and I guess the TEV regulates that. What affect this has on a R134 TEV regulating R12 I don't know...

If I replace the suction hose to the compressor then that only leaves two more to replace so I might go ahead and do that.

Russ,

The 90 degree elbo is on the suction hose to the compressor and after moving it from the right side to the left it comes up short. I tried to move the 90 degree elbo so it looks up to the ProCooler just ahead of the fender well, but then there's too much hose around the transaxle support. So between the wrong length and not being the modern barrier type I guess I'll just replace it and measure it to fit, I hope...

[kuehl]

Not all expansion valves (TEV) are created equal: you have tonnage ratings as well as superheat settings, and there are three different ways to rate the superheat of a given valve.
Most of the TEV's available, from the limited number of manufacturers, that fit the application here usually all fall within, to some degree, the same tonnage rating. However, the superheat rating of the valve, as designed, set and shipped from the manufacturer could vary from little to double or nothing. The key concern is usually avoidance of liquid, rather than vapor, making its way back to the compressor. And, what there is to gain by attempting to adjust a TEV is more of a gamble in the sense of things that could go astray (regardless of how many posts you have read on various forums by those who think they got a gain as a result of attempting to adjust the valve; whereas the gain could have been more likely related to a better evacuation and charge).

If you have an abundance of time and refrigerant to spare and you are anxious to get the ball moving I would suspect that you will not have a bad day by simply using the valve in hand and simply moving on with it.

[JFairman]

The superheat adjustment in the X-valve is the brass allen head adjustment you see when looking up the inside of the bottom.

I know talented mechanics that have worked on this alot here in south florida and experimented with it at length, and the superheat adjustment is very definately DIFFERENT for R12 and R134.
They told me they would be VERY angry at me if I said here how far and which direction to turn that allen head... oh well, I have to respect that because it is information they have earned.

I will say that R134 molecules are smaller than R12 molecules so there's a clue...

My friends '87 930 blows at 38 degrees using R134 with the evaporator blower fan on the medium speed setting while it is around 90 degrees out and the car is moving at city driving speeds.

All he did was put in a new nippondenspo compressor, new reciever dryer from pelican parts (not a procooler), a high quality 10" puller fan on the bottom of the origonal rear half bay condensor, and all new barrier hoses.

The origonal R12 condensors front and rear, and origonal evaporator and adjusted x-valve are still in place, and the evaporator box is not wrapped in thermal wrap.
Stahl motorsports in West Palm Beach, Fl. did the X-valve adjustment, flush, evacuation, and R134 charge for him.

I had to ride in the car, feel the very cold air, and see the analog AC thermometer with it's probe in the AC duct to believe it...

[ShakinJoe]

Jfairman is right. The valve can be adjusted. While R-134a has a higher HRE (net refrigerating effect) the compressor has to work harder thus nessecitating the need to open the expansion valve. Three turn counter clockwise. Mention above is the fact that the charges are not the same and MB does not even sell R12 TEV's anymore, well the charges are so darn close as the buld holds a mixture of products that mimc the saturation curve for the refrigerant used. R-12 and R-134a are alamost identical on a PT realtionship. Never mix them.

[glennspiegler]

Was asking about the Zims cooler kit for $599. It is an extra cooler for the rear fender well. Any experience, or is the procooler enough. When I do this project I will be replacing everything and changing to R134. Due to the decrease in R134 ability want to maximize it potential.

[tsuter]

The valves are not necessarily physically different but the adjustment is most definitely different for R134a v R-12.

Just like the above posts say.

Most the guys with R134a who can't get vent temps below 44-45 are running expansion valves adjusted for R-12! They then start adding wheel well condensers and extra fans.

Its all in the PVT tables discussed at length on some of these A/C posts. R134a to get cold must have low side pressures of 19-20psi. For R-12 to get cold, low side pressures of 30psi will do it. That's the role of the expansion valve.

Anyway I had a nice run to the Airport Diner this Sunday. Blowing 32-35F all the way.

Jeff at Rennaire in Houston would be a good one to chat with.

[T77911S]

go to polarbearinc.com and give them a call. very nice guy and he will answer all your questions.

[kuehl]

Mitch,
How much you open or close the valve all depends upon the valve's set superheat from the manufacturer. Ask the supplier to look up the superheat for the model valve you purchased. That will give you an idea of where to start..... provided the tonnage on the valve is sufficient for the evaporator's size and the heat load. Valves are typically 1.5 or 2 ton rated. And, for R134a valves being marketed today the range of the manufacturer's factory set superheat values can be anywhere from 5 to 20 for common externally equalized valves.

Superheat can be described as the difference between the refrigerant’s vapor temperature and its saturation temperature at some give pressure; the saturation temperature is a point where either the refrigerant vapor starts to condense or the refrigerant starts to boil (with TEV’s you are interested in the later). There is no "magic formula" for the number of turns because valves are not created equal (there different brands and different models for different refrigerants as well). It is very easy to run an evaporator too lean to the point where excessive low side pressures will starve your compressor of enough refrigerant/oil, make it work harder, and overheat ($$$). And it is just as easy to run an evaporator too rich to the point where liquid exits the evaporator and slugs the compressor ($$$).

If you don't know the current valve's factory set superheat value PM for a test plan.

[Mitch Leland]

Thanks Griff,

That's probably more technical than I can handle, I'll probably run what I brung... You/ve been too kind to offer your expertise.

[Mitch Leland]

Thanks Griff,

That's probably more technical than I can handle, I'll probably run what I brung... You/ve been too kind to offer your expertise.