AC fixed w/ ACC - might help you - Page 2 - PeachParts Mercedes-Benz Forum

leathermang · #16 09-17-2014, 11:18 AM

Quote:

Originally Posted by BillGrissom

Sort of not. Many people question how "flammable" is defined. R-134A also burns, and it produces poisonous phosgene gas as a product, which was used in WWI. Even R-12 burns. Stay away from the tail-pipe of a running engine after an accident in case the AC condenser is venting and getting sucked thru the engine.

You have missed the bigger physics and safety concepts.

Your compressor... particularly the R4 due to its lack of oil reservoir ... depends on the refrigerant oil being carried around the system by the refrigerant ... ( the measure of this ability is called ' miscibility ' ).
Few people question whether finely misted oil.... the result of the refrigerant being sprayed out into the air ... potentially onto hot exhaust or sparks produced in a collision...is flammable...
Having an obviously flammable carbon based gas... like Propane .... refrigerant carrier can't be as safe as a less volatile pressurized gas in case of fire.

BillGrissom · #17 09-17-2014, 03:36 PM

Millions of cars are using HC refrigerant, and nobody has reported a refrigerant or refrigerant oil fire, according to Duracool. It is used in home refrigerators in Europe. Duracool even paid for an engineering study that calculated that even if the entire charge leaked into the passenger compartment in 5 min, it wouldn't form an ignitable mixture. Of course, you would smell the mercaptin. One 6 oz can charged my 300D. If you shake the can, you would swear it is empty. Doesn't seem threatening, not like a 32 oz can of hair spray or (god forgive) the Sunday NY Times.

Actually, you would like the oil to remain in the compressor, not circulate where it decreases heat transfer in the coils. I use PAO 68 oil, which is supposed to stay put better. GM guys are at a disadvantage since their R4's are mounted high. I don't know how PAO 68 burns relative to mineral or PAG oils. My guess is that if refrigerant oil sprayed on the exhaust pipe, it would simply cool the metal and not ignite. A slightly educated guess since my M.S. thesis was in heat transfer and Phd study in combustion.

leathermang · #18 09-17-2014, 04:46 PM

Quote:

Originally Posted by BillGrissom

Millions of cars are using HC refrigerant, and nobody has reported a refrigerant or refrigerant oil fire, according to Duracool. It is used in home refrigerators in Europe. Duracool even paid for an engineering study that calculated that even if the entire charge leaked into the passenger compartment in 5 min

Well , Duracool is certainly an unbiased reference...LOL

How many miles per hour do refrigerators in Europe travel ?

I am not concerned with leaking into the passenger compartment.

I am concerned with it promoting a fire in the engine compartment during an accident which might not happen if a combustible gas under pressure and incorporated with oil were not present.

Graham · #19 09-17-2014, 08:05 PM

Quote:

Originally Posted by BillGrissom

Millions of cars are using HC refrigerant, and nobody has reported a refrigerant or refrigerant oil fire, according to Duracool.

Bill,
In Canada, our laws concerning refrigerants are more stringent than in USA. For example, we cannot just go down to Walmart and buy R134a like you can. In fact we can't buy it at all retail. The regulations for R134a are very stringent and if a shop feels there is a leak, they have to evacuate the system before giving you back the car - no topping up or recharge until leak is found and repaired.

However, hydrocarbon based refrigerants like Duracool and Red Tek are readily available at auto stores and are not regulated. I am sure most owners of old cars use them because the alternative is just too difficult to deal with.

I asked our best local A/C shop about repairing my 85 300D's A/C (It also seized and broke belt some time back). It had been converted to R134a, but they RECOMMENDED using Duracool. Likely because they felt old R12 cars are prone to leaks and they realize the average guy can't bring the car in and have R134a system repaired every couple of years.

Luckily we don't have that much very hot weather. Only 1 of our 4 cars has working A/C

leathermang · #20 09-17-2014, 09:39 PM

One thing to keep in mind with regards to someone having an R4 is the lack of an oil reservoir ... thus.... whatever refrigerant you use... its miscibility with regards to the oil you are using is critical... this is one of those things which does not get researched when the system fails.... so feedback is not available....

BillGrissom · #21 09-17-2014, 09:57 PM

I sure wouldn't convert a car to R-134A since it is soon to be replaced. I wonder what surprises are in store with R-1234YC (or whatever its called). Low price is probably the least likely. I have read that PAO 68 is the best oil to use today with any refrigerant, because it is the least miscible, doesn't absorb moisture (like PAG), and works for any specified viscosity. That it coats the condenser and evaporators less gives better efficiency, at least that is the claim. I can't say I notice any improvement over the R-12 & mineral oil I used to have in my 300D's.