Posted From: 18.104.22.168
|Posted on Saturday, 01 November, 2014 - 11:22: |
In my quest to find out about stuff.
I have been snooping around fridges.
R12 is effectively banned because it damages the ozone layer some say it doesn't and some also say that volcanoes emit much more cfcs than du Pont have made in total, I haven't clue as to the truth. The science behind the ban is there to read if you want.
The replacement is R134a which is a Hfc and it also damages stuff and decomposes into mustard gas in a vehicle fire. Fortunately in general there's less than a kilo of 134a to decompose and most of that will vent and escape before the fire gets it.
There are other gases such as CO2 nitrogen and argon but these require more pressure. Low side and high side pressures are 20 and 200 bar for CO2. 300 and 3000psi. The fridge guys are working on such a system for cars because despite the high pressures the efficiency is high and the system about a third of the size.
However hydrocarbon gases such as butane methane and propane are good refrigerants that work at the same pressures as R12 and are 10% colder than R12 and 50% colder than R134a.
These gases are known as R12a.
The guy who explained this yo me said his old jag aircon is running on 90% propane 10% nitrogen mix. The nitrogen absorbs moisture and the propane is extra refined. Because the compressor oil is hc based mineral oil the hc propane does not cause any reaction. Propane is aalso ok with pag and ester oils used in Hfc134a. Also added is a small amount of ethyl mercaptin stenching agent and a small amount of dye. Plus propane doesn't go acidic should moisture get in.
He also said that some have been using blow lamps to charge the system without even taking out the R12 or 134a. Which will eventually lead to problem because the operator has no way of knowing how much is going in. Plus the system has not been drawn down to Zero psi absolute. At best it's zero psi gauge.
Best to use a gauge and run the compressor and go to book pressure on the low side.
Because propane is better than R12 only half the weight of gas is used. The compressor uses 40% less power which on ageing systems is good plus less fuel used.
Safety....propane is inflamable. However it has been calculated that the odds are like winning the lottery jackpot.
The stenching agent will alert that the system is leaking. For propane to explode it requires oxygen. Which means a leak. I think in a front ender the condenser will rupture and the propane will disperse into the atmosphere. However a small slow leak inside the car could explode but the smell would be obvious.
The law. Oz kiwi and some states of America it is illegal. In some states the car has to be fitted with 134 adaptors first.
Europe is different and as far as I can tell not illegal.
Canada has a company called Duracool. Which makes the charge hoses and 6 oz cans of fridge grade propane $8 each. The hose with gauge is 20 bucks or so reusable.
Accidents .....there have been accidents with fridge propane not many. Caused by engineers not realising that propane is in the system and doing something stupid like venting to atmosphere and sparking something. So should one use propane a warning sticker is available.
Note if you are unsure read the internet. If you are still unsure go to ac shop and they will stick 134a in which does work providing the conversion from R12 is done correctly.
I get the impression that the fridge bit is simples, but it's more complicated with all the flaps and actuators.
(Message approved by david_gore)
Posted From: 22.214.171.124
|Posted on Tuesday, 04 November, 2014 - 12:02: |
I have been mucking around with an air con system on a rover.
the system has been in bits when the car was rebuilt last year and has no R12. The compressor is a Delco A6 which is about the same as a SY one.
How the system was repaired.
First vacuum the system to check for leaks none found.
Remove compressor and empty the oil out no oil. So we added 8 fluid ounces to the compressor and 2 in the new dryer.
Vacuum to 29 plus " for 1 hour.
Fill with nitrogen to 20 psi. For 10 ten mins.
Vacuum to 29 then fill with R12.
The vacuum pump used costs £700.
the workshop temperature was 22 centigrade which helps the damp in the system boil, at 10c it would be harder to remove the damp. Also the engine was warm which also helps.
Any air left in the system will lower efficiency because air is not a good refrigerant and is taking up space. Plus with the air will be moisture which can freeze inside and block the expansion valve and other small holes.
It gets worst. The water will react with R12 and 134a And form acidic sludge. And more bad news 134a uses pag or ester oils which is hydroscopic like dot. R12 uses mineral 525 Frigidaire oil.
The whole job above cost £75 Labour plus dye, R12, fridge oil and nitrogen which added £80.
The R12 used was reclaimed stuff supplied by BOC.
With out a vacuum pump that can pull to 29.5 inches of mercury it is not possible to diy. If the system is not vacuumed then one has no way of getting the damp out which will damaged any system running 12 or 134a.
It is possible though to use a domestic fridge compressor and having an ambient temperature that is 25 c plus. Which in the UK I would suggest in the summer would be best.
When the customer came to pick up the car he sat in the car with the owner and explain how to get the best from the aircon.
The aircon guy reckons that most owners don't understand how to use the air con and they either have it flat out or off. Instead he says turn it down to minimum and use every week to keep system good. Most don't turn the system on in the winter which causes the seal behind the compressor clutch to dry out and lose a bit of Freon. Hopefully the rover compressor seal is the later double lip type.
(Message approved by david_gore)
Post Number: 163
|Posted on Tuesday, 04 November, 2014 - 20:09: |
Bob, you were lucky to get R12, I was told this was totally unavailable years ago, and now illegal to fill systems with . I have been using RS24 which is a drop in replacement in my vehicles on the garage's advice for years. However this is not as cold as R12.
Post Number: 205
|Posted on Tuesday, 04 November, 2014 - 20:23: |
I was under the impression the ban was on the manufacture of R12, not the use of it.
So reclaimed would be fine (although sources of it will eventually dry up).
As of a year or two ago, I think you could even still get new (old stock) R12, but perhaps that's all gone now.
Post Number: 3117
|Posted on Tuesday, 04 November, 2014 - 22:19: |
Surely R12 is like Four-Star leaded petrol (we simply called it Super in Australia), chloroform anęsthetics and kerosene-fired refrigerators with porous plugs. No longer relevant and best forgotten.
Post Number: 164
|Posted on Tuesday, 04 November, 2014 - 22:27: |
Richard I quite agree, if it is not easily available on going, then its not worth bothering with, hence my use of RS 24 which is readily available in the UK.
Posted From: 126.96.36.199
|Posted on Wednesday, 05 November, 2014 - 09:08: |
I too in view of the expense and environmental concerns wondered why R12. But the customer insisted. R134A is about to be banned in Europe. Which leaves only R12a propane and RS 24 butane/hfc. Out of the two I prefer 12a. Because it has zero hfc and air in the system lowers efficiency and doesn't cause damage. Also if nitrogen is added in small amounts then the moisture is absorbed should a bit somehow get in.
The flash point of 12a and 24 is 1700c and 134a is 1300c.
Another is R600 butane.
R 600 goes liquid at 35 psig. This means that the low pressure side is very low
25 psia or minus 5psig.
I also was shown a system that vacuums itself. The high pressure outlet from the pump has a cap which goes to atmosphere. Next to that is a valve. The cap is removed and the valve closed. The compressor is then run which vacuums the system. Then while running the cap is refitTed and the pump stopped. Then the valve is opened. The throttling valve has a small bypass which allows the vacuum to pass into the evaporator, the expansion valve,
the drier and last the condenser. The vacuum can go no further because the valve is shut. Then the fridge gas is allowed in via the low pressure port until the correct weight on the spring balance is shown.
Safety and environmental.
all refrigerants are inflamable including R12 R134a and RS24. It is illegal to vent the above to atmosphere by knowningly putting stuff in a system that leaks or by venting just to check for pressure or as a disposal method.
R12a and R600 are inflamable but have arrestor additives. Venting to the atmosphere is not illegal in Europe. However it is illegal to purge using the gas as a purgent.
R12 and 134a are both ozone or otherwise nasty, and as bad as each other. RS24 is not as bad.
R12a propane is to me the best bet as it a stable refrigerant that is environmentaly friendly and kind to elderly air con systems. Plus it is so cheap that the air con guy reckons if R12a is chosen as a replacement for 134a then he will be able to give it free when doing aircon work. The cost for a shadow for R12a is £6. Hopefully my compressor seals are good.
A car has petrol or lpg automatic oil, dot and other inflamable stuff so a couple of litres of propane isn't going to hurt.
Suppose the evaporator sprung a leak which takes say 2 months to leak all the propane out. In that time the propane would leak out of the car, if a door is open then with in seconds any propane will go in seconds. Plus a nasty niff of mercaptin. Huge fast leaks don't happen unless there's an accident and the condenser gets it not the evaporator. I would be more worried about the displacement of air which applys to all refrigerants.
Du Pont said that the problem is that as soon as inflamable gas is mentioned the Hindenburg airship disaster comes to mind.
Greenpeace and friends of the earth both recommend hydrocarbon refrigerants mainly propane and isobutane and mixes of the two. There are 400 million fridges running world wide on isobutane R600.
(Message approved by david_gore)