How do you know if the air con is packing up?

If the gas leaks out, the a/c loses efficiency. Why regas before that point is reached?

How does moisture get into a pressurised system?

It's a lot cheaper

Unless the system has been unused for some time, or been left standing without gas, it's unlikely the seals will need replacing even if the system has lost a little gas over time.

A cars a/c system is working perfectly. The temperature differential is within acceptable limits, meaning their are no significant leaks. Why change the gas? Refilling it with similar gas to that taken out seems pointless to say the least. Domestic freezers and fridges often run on the same gas for decades. What makes a cars a/c so different? The lubricant that was added to the gas on the initial filling is still there. Moisture or impurities can't get into the system as long as it's under pressure. I'm not going to accept a recommendation to change the gas without being given a logical reason for doing so. Mike.

Just guessing but maybe it uses the gas pressure to push the seals onto the drive shaft and as the pressure falls the seal weakens and lets out more refrigerant.

Car compressors are driven from the engine so they have a rotating shaft going through the seal. Domestic units have the motor and compressor completely sealed in a tin can so they can't leak. I think I heard at some time that BMW were going over to 42v electrics so that they could used the sealed tin can compressor with an electric motor so that it wouldn't need to be regassed.

I don't know the answer as to how but the systems do contain a dryer to hold what moisture does get in so maybe it permeates through the rubber or something. I can't imagine them putting dryers in if all they had to do was ensure they used dry gas.

The summer before my compressor seals failed I was getting condensation on the outside of the windscreen at the bottom when the air conditioning was running and the air coming out was at -4 degrees C. MAybe if I'd known to have it regassed then the seals wouldn't have failed.

Granted, but the point remains. If the system is working properly, it hasn't a significant leak, so why change the gas because it's a year old?

I did know that. I was questioning the idea that the gas had to be changed, because in some way it degrades over time.

I think I

Thus supporting my argument that a/c systems only need regassing if and when gas loss reduces efficiency to an unnacceptable level.

I would suspect a drier is used to dry the gas when the system is filled. If not, maybe someone can explain how moisture gets into a pressurised system.

I don't understand that. How can the a/c work if the compressor seals have failed. No pressure... no a/c.

It's obviously in the interests of those that service a/c systems, to convince owners that systems need regular maintenance. I would question the value of servicing at regular intervals, rather than servicing when the system shows signs of a problem. Mike.

The car a/c can't ever have a perfect seal though. The refrigerant molecules are so small that there will always be some escape and they are likely to take some of the oil with then.

I've seen systems that take the gas out and dry it but I know my system also has a drier inline and that makes me assume that some moisture must get in somehow, capillary action, osmosis, I don't know.

The seals hadn't failed when it started running at -4 and I'm only assuming that running it at the lower pressure, but before the low pressure switch activated, that it did damage the seal, the car was 4 years old at that time. I'll never know if the seals wouldn't have failed if I had had it regassed then but with that experience I would always have it regassed after 3 years in the future.

The point about R12 is that it is extremely ecologically UNfriendly. All systems lose pressure over time. The modern recharging stations remove and clean the refrigerant, then after vacuuming down (which checks for leaks) refill with the correct quantity of gas (plus most places insert a leak discloser and some oil) After recharge the outlet temp is checked, the pressure differentials are checked and early signs of failure are found.

Some places also flush out the oil, replace the dryer and the oil (which is what holds the oil) which is more expensive.

I think that if you check up, all manufacturers will recommend a gas check and charge every few years.

Ignore the checks at the peril of your wallet, as in my experience regularly checked systems rarely fail. A failure usually is several hundred pounds worth at a minimum, a check/recharge is usually 50 - 100 pounds depending where you go.

mrcheerful

That's the main difference. domestic fridges etc. are far smaller in terms of the heat moved & the motor & compresser are all sealed inside the tin, on a car you've got a drive shaft with seals to the outside world

Well you can stick a pressure guage on & check if you like. You have to lose a very large percentage of the gas though before the pressure drops to the point where it cuts out & given how little it costs to vacuum & regas it evry 3 years compared with any maintenance work on the system it seems like cheap insurance. You pay your money & take your choice.

Granted, and from what I understand, loss of pressure is the most common reason for a/c failure.

That may be the case, but is it necessary? IMO it's not.

IME nothing could be further from the truth. To suggest that failing to have a system checked on a regular basis is 'usually' going to cost 'several hundred pounds worth at a minimum' when it does fail, is nonsense. Most failures are due to a gradual loss of gas over a period. The fix is to simply regas the system, after checking for any obvious leaks.

As for not having regular checks being expensive on ones wallet. I've had a/c or climate control on my car or cars since 1988. During that time non have been serviced as such. Only once have I paid for regassing, after a condenser sprang a leak, which I repaired, rather than replacing it. I don't think I've been particularly lucky. I believe a/c systems are fundamentally reliable, and expensive mechanical repairs are the exception rather than the rule. I also believe that regular servicing is a waste of money. Obviously you don't agree, so I think we'll just have to agree to disagree. Mike.

Why does that mean the gas has to be changed. How does a shaft with a seal affect the quality of the gas?

So are you saying that an unserviced system that is repaired as and when necessary is going to cost more in the long run than one that is serviced on a regularly basis? All I can say is that that is not my experience at all. I suspect that your view is based on what a/c engineers would like you to believe, rather than on personal experience. Mike.

Cos it can leak, look at a fridge & it's completely sealed. You regas commercial refridgeration units too as they're not completely sealed.

Well as I say you pays your money & takes your choice, at least two people I know apply that approach to engine oil & so far they'd agree with you.

All AC systems have a drier to remove water vapour - and unless you have a major leak should last the life of the system. If new parts are needed it's usual to replace this drier.

As regards seals failing prematurely, this is usually down to the AC not being used for long periods - like the UK winter.

. Only once have I paid for regassing,

Fairy nuff.

mrcheerful