Why do car air-cons lose gas, but domestic fridges don't?

Bendy_House

The recent hot spell has highlighted that my car's air-con ain't working. Ho-hum - looks like I need a 'gas.

Google suggests I shouldn't be too surprised if this needs doing every couple of years! (First time - and car is 7 years old, so mustn't grumble.)

But, why do domestic sealed systems - fridges, freezers, air-cons etc keep going forever, seemingly without loss? Where is the natural 'leak' in a car?

Mr.Generous

There isn't a natural leak, but if you bounced your fridge on and off speed bumps at 30 mph for 5 years it might also spring a leak.

grumbler

Mr.Generous said:

There isn't a natural leak

Well, in a fridge the compressor is driven by an electric motor that is sealed together with the compressor in an air-tight casing filled with oil.

 AFAIK, in a traditional car it is usually driven mechanically - by the engine and a belt. I think, this makes it impossible to seal it perfectly.

Bendy_House

That makes sense, Grumb. Yes, most car systems are driven off a drive belt, and are engaged via an electrically-operated clutch. So that means there will be a spinning shaft running through a presumably-rubber seal, which won't be perfect, 'specially for a pressurized gas.

So a fridge's comp motor is sealed inside the unit? Wow. Cooool.

grumbler

Bendy_House said:

So a fridge's comp motor is sealed inside the unit?

I bet you saw it many times.

Alanp

With car air con it depends on how it’s used, if it’s only used during hot weather, then the oil in the system doesn’t lubricate the seals, then they dry out and leak, best to leave air con on all year and just adjust the heat settings,  I’m assuming a fridge is the same , and is on more or less constantly so seals won’t dry out..

Bendy_House

grumbler said:

I bet you saw it many times.

Yup!

Thanks Grumb. Wow - two wee pistons rattling away. So that's why they make a 'purring' sound!

I wonder why car air-cons aren't electrically-driven? They can be that high a power drain, can they? Much much simpler than a permanent belt drive and an electric clutch?

There must be a good reason.

chrisw

Bendy_House said:

grumbler said:

I bet you saw it many times.

I wonder why car air-cons aren't electrically-driven? They can be that high a power drain, can they? Much much simpler than a permanent belt drive and an electric clutch?

There must be a good reason.

You can buy 12v compressor fridges but they are very expensive, 12v fridges are usually thermoelectric instead which are much cheaper to buy.

So I suspect it comes down to economics  in the end.

Bendy_House

Yup, it must do, Chris. Cheers.

grumbler

 Reportedly, a car air conditioner needs about 3kW power - much more than a 12V fridge. You'll need a huge generator for such power. Normal generators (alternators) are less than 1kW, and you'll need extra 3kW.

Moss5

It's all changed for hybrid and electric cars. My Hybrid has a 300V DC compressor.