Technical How much does it take?

[KungFooPanda]

I’m getting my 2007 air con re-gassed and I was wondering how much R134a the ?hp takes. Could also do with knowing if this takes PAG 46 compressor oil and the quantity please.

?

 

[portland_bill]

The question suggests you are planning to regas it yourself. Not a good idea.

Take it to an aircon specialist, (actually most garages can do this now). They have the equipment to extract the remaining gas, then do a leak test, and regas with the correct quantity of gas and the correct oil. Their equipment supplier will supply them with teh specs for each car. Usually you only pay for the additional gas used.

 

[KungFooPanda]

The question suggests you are planning to regas it yourself. Not a good idea.

Take it to an aircon specialist, (actually most garages can do this now). They have the equipment to extract the remaining gas, then do a leak test, and regas with the correct quantity of gas and the correct oil. Their equipment supplier will supply them with teh specs for each car. Usually you only pay for the additional gas used.

Not really thinking about doing it myself. I just like to know how much gas and PAG46 oil it takes. ?

 

[DaveMcT]

The gas is harmful to stratospheric ozone (though less than the old CFCs) and is a powerful global warming gas so should not be simply dumped or topped up without leak testing.

Fridges are now using butane. Who knows why cars don't.

https://en.wikipedia.org/wiki/Butane

 

[portland_bill]

The gas is harmful to stratospheric ozone (though less than the old CFCs) and is a powerful global warming gas so should not be simply dumped or topped up without leak testing.

Fridges are now using butane. Who knows why cars don't.

https://en.wikipedia.org/wiki/Butane

My new fridge took a lot longer to get down to temp than the previous one, suggesting butane is not as efficient. With a fridge that shouldn't matter much as once cold it just has to maintain that. With car aircon, we need to cool the air as it enters, at a rate that makes a difference. Perhaps with butane we'd need a cooling unit on the roof to handle the airflow, like refrigerated vans. Just a guess. Also, if butane did the job well, surely we'd have been using it for years.
My latest fridge is also significantly smaller inside due to the increased insulation. A real pain having to shop in smaller quantities and more often. Is this another suggestion that butane is not as efficient?

Are there any physicists out there with an answer.

 

[DaveMcT]

I would like to know why cars don't use it but suspect the real reason is homologation costs.

Regarding domestic fridges - if the coolant itself was less effective they would not be able to achieve the triple A ratings they all strive for. Single phase electric motors are not very efficient (check out the heat thrown out from vacuum cleaners. Fridges and freezers these days have smaller compressors (less power in = less used) but they take longer to get down to the set temperature. Laundry machines have gone the same way. Three hours to do a wash cycle is way longer than the older machines needed but uses less power.

The next step will be electronic controlled multiphase motors but costs will rise so not yet.

Edit - Found the answer

Very pure forms of butane, especially isobutane, can be used as refrigerants and have largely replaced the ozone-layer-depleting halomethanes, for instance in household refrigerators and freezers. The system operating pressure for butane is lower than for the halomethanes, such as R-12, so R-12 systems such as in automotive air conditioning systems, when converted to pure butane will not function optimally and therefore a mix of isobutane and propane is used to give cooling system performance comparable to R-12.​

Wikipedia

 

[jrkitching]

Fridges are now using butane. Who knows why cars don't.

It's both extremely volatile and extremely flammable. You wouldn't want a ruptured aircon line spewing butane over a hot engine in the event of a crash. There are probably a shedload of other good technical reasons, but that one will do for me.

 

[DaveMcT]

It's both extremely volatile and extremely flammable. You wouldn't want a ruptured aircon line spewing butane over a hot engine in the event of a crash. There are probably a shedload of other good technical reasons, but that one will do for me.

How about a ruptured petrol line spraying out of the plastic air inlet manifold in the event of a crash? Or a short circuited battery exploding acid all over the place? Or an LPG line failing in a crash with a pressurised tank containing gallons of the stuff. Butane is a component of LPG and petrol.

The amount of gas in an aircon system is very small and will quickly disperse though any hole. But any change will demand homologation and it's associated high costs.

CFCs were invented to make money though they were better refridgerants than ammonia based systems. The same inventor came up with the incredibly toxic Tetrethyllead that was only quite recently removed from petrol.

To be fair, Midgley died in 1945, but back in the early 1970s, my dad was saying to avoid using aerosol cans because they damage the atmosphere. I'm sure he had no idea why, but it shows the folly of CFCs was not a recent discovery.

These days, aerosol cans use butane. All that explosive gas retained by a little plastic valve, yet nobody stresses about them.

Again a Wikipedia quote:

Very pure forms of butane, especially isobutane, can be used as refrigerants and have largely replaced the ozone-layer-depleting halomethanes, for instance in household refrigerators and freezers. The system operating pressure for butane is lower than for the halomethanes, such as R-12, so R-12 systems such as in automotive air conditioning systems, when converted to pure butane will not function optimally and therefore a mix of isobutane and propane is used to give cooling system performance comparable to R-12.​