A/C questions, yes more!

The 2 electrical connection are the in and output of hi/lo pressure switch to cut to the a/c clutch in case of too low or too high pressure, and they will trigger at the same time the yellow warning light in the check control system when the power is cut to the clutch.

My car runs on a converted system and the max pressure was set to about 85% of original to safeguard against old equipment blowing up (evaporator, condenser)

 

Its propane. You want pressurized propane in the engine bay?

 

Hi Brian,

But with the same flashpoint as R134a? I don't understand why the propane mix with additives to increase the flash point is any different than R134a? Please explain?

Thanks in advance.

Here below is the product comparison table from Red Tek 12a (redtek.com). Unless they are lying, the flashpoint for R134a and the Red Tek 12a are the same (fourth line from the bottom). The flash point for Red Tek 12a only applies for concentrations from 1.6 % to about 8%, anything other than these concentrations will not flash. In addition, the charge of HCFC is one-third of the charge of R-12 therefore the amount of refrigerant in the system is reduced considerably (second line from the bottom in the table below). If you look at the EPA SNAP (Signifcant New Alternatives Policy) approval list you will find similar propane based products approved for Motor Vehicle use (http://www.epa.gov/ozone/snap/refrigerants/lists/mvacs.html). And, with lower head pressures associated with the HCFC products the possibilty of leaks are reduced compared to R134a, even though this may be marginal.

Product RED TEK® 12a R12 R134a
Chemical Type HC CFC HFC
Composition zeotrope pure pure
G.W.P (CO2=1, 100yr ITH) 3 10,600 1,600
O.D.P. 0 0.9 0
Atmospheric Life < 1 year 130 years 16 years
Thermal Performance +12 - +32% 0 -8%
Oils both mineral synthetic
Leak Detection hydrocarbon halide halide
Boiling Point (C) -31 -30 -26
Autoignition (F) 1385 n/a 1385
Latent Heat (1.0 bar, abs) 367 KJ/kg 145 KF/kg 189 KJ/kg
Refrigerant Mass Charge Size (R12=100%) 33% 100% 90%
Toxic Thermal Decomposition None Phosgene Gas Hydro Flouride Gas

I have no commercial interest in any of the products that I mention. I am only an interested bystander looking for reliable information. I consider you a source of reliable information.

Kind regards,

 

Gasoline as a liquid in a engine bay is flamable, but not explosive. Gasoline vapors are explosive. Propane in an engine bay is more explosive. In an accident, it is more dangerous than freon. Propane has been used for many years as a refrigerant. It is very efficient, inexpensive, and not bad for the environment, as well as less stressful on the equipment, but because of the increased dangers it only has limited applications.

 

1385 degrees F is the flashpoint for both R134a AND the modified propane used in refrigeration. I am not talking about Freon 12 which has no flashpoint. EPA considers these modified propanes safe for automotive use.

 

Lots of controversy over the R-134a replacement as well due to flammability concerns.

HFO-1234yf was developed to meet the Euro directive aimed at reducing global warming. While it has been adopted by GM (and implemented) France and some German manufacturers are hesitant.

www.en.wikipedia.org/wiki/2,3,3,3-Tetrafluoropropene

However, the Mondial's A/C system was designed for R-12 (which is still available in some areas). Anything else is an inefficient work-around.

 

It has been pretty well established that the additives that are used to render the propane safer separate and leak out over time leaving the propane. That is why it is not considered industry acceptable.

 

Fuel systems are designed for zero leakage and remain that way quite well with minimal service. Not true of A/C systems.

 

Leak out after how much time? i sure would like to see a reference for that. Nothing in the EPA stuff on line.

 

My cousin uses propane in his old Lincoln and gets very very cold air. Propane has been used in home a/c in the old days. In a car the amount of propane is very small and pales in comparison to 20 gallons of gasoline.

 

As far as I can speculate without real data, the Material Safety Data Sheet from Red Tek 12a only mentions propene and butane. But they do not list the real ingredients, only these two in the toxicology section which have published toxicology data. The 12a mixture is listed as "alkanes" which, if there is propene in the mix, is an "alkene" not an "alkane". I am not familiar with how much leeway the manufacturers have in the description of their product when they want to keep the formulation secret.

Rifledriver has seen data on the differential leaking of components which, after some time, leaves pure propane. I have asked for a reference. Red Tek 12a cautions against the use of butyl rubber tubing apparently due to Red Tek 12a's permeability through this tubing.

 

Mark, you are welcome. As far as I know the receiver/dryer should be changed every few years as it accumulates not only moisture but also other debris. The pellets capturing the humidity will become saturated and eventually break down and start clogging the expansion valve. The humidity will build up and start corroding the internals of the a/c system.

The min/max pressure switch just screws into the side of the in/outlet of the dryer. Are you sure there is no position for it?
My car's dryer was a standard item sourced locally when I switched from R12 to R134a. The switch exists with different pressure thresholds. You may want to check your dryer top and see if there is a position for a switch.
Image Unavailable, Please Login

 

No and no. I would also go with automotive-industry solutions.

 

Can you fit the min/max pressure switch into the Schrader valve position?
Also, there are 2x2 connections (2 combined on either side of the min/max pressure valve, for the check control signal, condenser and a/c clutch, plus the actual input.
It looks like your original setup had a separate lo and hi pres velave.

 

I think you need this pressure sensor which is both Max and Min sensor. It mounts on the male connector.
Image Unavailable, Please Login

 

Very interesting articles concerning the safety of the new tetrafluoropropene which produces hydrofluoric acid upon burning with the lubricating oil found in the compressor.

This is from Wikipedia article mentioned by Wade above BUT the references are NOT from Wikipedia.

"Although the product is classified slightly flammable by ASHRAE, several years of testing by SAE proved that the product could not be ignited under conditions normally experienced by a vehicle. In addition several independent authorities evaluated the safety of the product in vehicles and some of them concluded that it was as safe to use as R-134a, the product in use in cars today. In the atmosphere, HFO-1234yf degrades to trifluoroacetic acid, which is a mildly phytotoxic[8] strong organic acid[9] with no known degradation mechanism in water. In case of fire it releases highly corrosive and toxic hydrogen fluoride.

In December 2012, it was reported that tests by Mercedes-Benz showed that the substance ignited when researchers sprayed it and A/C compressor oil onto a car's hot engine. Stefan Geyer, a senior Daimler engineer who ran the tests, stated "We were frozen in shock, I am not going to deny it. We needed a day to comprehend what we had just seen." Combustion occurred in more than two thirds of simulated head-on collisions. The engineers also noticed etching on the windshield caused by the corrosive gases. BMW, and VW-Audi agreed with Mercedes and left the SAE R-1234yf CRP Team, stating that the performed tests are not sufficient to fully judge the safety of their vehicles. The German Automakers have been leaning towards carbon dioxide refrigerant which is safer for both passengers and the environment.

Following Mercedes claims that the new refrigerant was unsafe, Germany's Kraftfahrt-Bundesamt (Federal Motor Transport Authority) ran a series of tests. The Authority concluded that while the substance was potentially more hazardous than previously used R-134a, it did not comprise a serious danger. However the German Automakers disagree with their findings, and test procedures. [13] Following other independent and in house testing, General Motors still plans to transition all new models to the new refrigerant by 2018. Chrysler announced that they would continue the transition to R1234yf as well".