DIY Aircon top up.

[norseman]

It's interesting to compare that with the automated drain, measure, vacuum, refill, new oil, test
£60 at places like kwikfit. .

I might be lucky then, last week's re-gas carried out by my local garage was on what looked like a new Sun machine ... it was certainly the shiniest piece of kit in the workshop & I've not seen it there on previous visits

 

[Bodgedbuild]

I have reservations about using a DIY top up kit, not because it is a bad product but because it has the potential to cause damage if not used correctly.

1/ I would first check there is at least some pressure remaining because if there is none at all, the system has a leak and since the Kyoto summit it is illegal to refill a system that is known the leak. Obviously there would also be no point in proceeding anyway!

2/ I would start with a totally cold engine and car interior as cool as possible as you will get the refrigerant in far more easily because the stuff in there has not been heated up already. Really the tin needs to be warmer than what is in the car.

3/ To keep it as safe as possible you would need to know if the connector is either sized for low or high side ports. I'm guessing low side (small port). As this side is subject to a much reduced pressure while the AC is running it tends to draw the gas from the can but it really does need to be a gas and not a liquid so it is important to know which way up the tin should be to discharge as vapour/gas. This is important because the pistons or vanes within the compressor can hydro-lock in the same way a car engine can so liquid should only be introduced in the high side, after the compressor. Logically I would think it should have no dip tube in the tin and if so it should be kept totally upright.

4/ To avoid charging a small amount of air (and hence moisture) into the system, a very small amount should be "purged" to fill the tube and gauge supplied with the tin.

5/ Obviously the amount of r134a to use is not going to be assessed by weight so I would probably add very short bursts while taking vent temperatures and not add much after it starts to go cold. I guess the temptation would be to add loads but this would either damage the system or result is "slugging" when the refrigerant does not change from liquid to vapour as it expands. You would then get a system that goes hot/cold, hot/cold in cycles. This would also happen but more slowly if there is ice in the system, which occurs when air gets into the system.
As another note, I believe some of these kits may not be pure r134a but a blend, if this is the case it must be charged as a vapour so I really would hope it has a low side port connector?
The only other problem I can see with a small tin, is the thing freezing up if it is vapour charging into the low side?

I'd be interested to see the instructions if anybody has one of these kits?

 

[Avocet]

I know there's not much in it but I get the hose and gauge and hopefully it will do more than one top up, and I'll find out for myself once and for all whether they work.

Oh they certainly work (especially if you get a reputable one like the one illustrated in the earlier post, that actually contains R134a rather than some magic potion that is supposedly "R134a *compatible* ")! However, I don't think they do you system any favours in the long run.

 

[Avocet]

I have reservations about using a DIY top up kit, not because it is a bad product but because it has the potential to cause damage if not used correctly.

1/ I would first check there is at least some pressure remaining because if there is none at all, the system has a leak and since the Kyoto summit it is illegal to refill a system that is known the leak. Obviously there would also be no point in proceeding anyway!

2/ I would start with a totally cold engine and car interior as cool as possible as you will get the refrigerant in far more easily because the stuff in there has not been heated up already. Really the tin needs to be warmer than what is in the car.

3/ To keep it as safe as possible you would need to know if the connector is either sized for low or high side ports. I'm guessing low side (small port). As this side is subject to a much reduced pressure while the AC is running it tends to draw the gas from the can but it really does need to be a gas and not a liquid so it is important to know which way up the tin should be to discharge as vapour/gas. This is important because the pistons or vanes within the compressor can hydro-lock in the same way a car engine can so liquid should only be introduced in the high side, after the compressor. Logically I would think it should have no dip tube in the tin and if so it should be kept totally upright.

4/ To avoid charging a small amount of air (and hence moisture) into the system, a very small amount should be "purged" to fill the tube and gauge supplied with the tin.

5/ Obviously the amount of r134a to use is not going to be assessed by weight so I would probably add very short bursts while taking vent temperatures and not add much after it starts to go cold. I guess the temptation would be to add loads but this would either damage the system or result is "slugging" when the refrigerant does not change from liquid to vapour as it expands. You would then get a system that goes hot/cold, hot/cold in cycles. This would also happen but more slowly if there is ice in the system, which occurs when air gets into the system.
As another note, I believe some of these kits may not be pure r134a but a blend, if this is the case it must be charged as a vapour so I really would hope it has a low side port connector?
The only other problem I can see with a small tin, is the thing freezing up if it is vapour charging into the low side?

I'd be interested to see the instructions if anybody has one of these kits?

An excellent post, if I may say so. (And yes, they all connect to the "low side" port). The "High side" will be several hundred PSI with the pump running, so nothing will leave the can - quite the opposite, in fact)! The low side, at the point just after the compressor cuts in, will only be a few tens of PSI. On some systems, it can be very low indeed - close to atmospheric pressure, in fact. That's one of the problems with these "one-size-fits-all" gauges that have a green zone on them. On pretty much every "healthy" car I've tried one of these gauges on, the topup can gauge has either told me it needs gas, or it has been right near the bottom of the green zone.

Lastly, some people stand the top-up bottle in a bucket of hot water (especially as the can starts to get closer to being empty), to encourage the gas to leave it.

 

[Bodgedbuild]

An excellent post, if I may say so. (And yes, they all connect to the "low side" port). The "High side" will be several hundred PSI with the pump running, so nothing will leave the can - quite the opposite, in fact)! The low side, at the point just after the compressor cuts in, will only be a few tens of PSI. On some systems, it can be very low indeed - close to atmospheric pressure, in fact. That's one of the problems with these "one-size-fits-all" gauges that have a green zone on them. On pretty much every "healthy" car I've tried one of these gauges on, the topup can gauge has either told me it needs gas, or it has been right near the bottom of the green zone.

Lastly, some people stand the top-up bottle in a bucket of hot water (especially as the can starts to get closer to being empty), to encourage the gas to leave it.

Despite my tag, even I wouldn't liquid charge into the high side with it running!

 

[Avocet]

Despite my tag, even I wouldn't liquid charge into the high side with it running!

I don't think it would ever be possible, to be honest. I think the real danger, is putting liquid into the low side and it then getting sucked into the pump. I've never seen it happen though. Normally, if the pressure is low, then by definition, the liquid will evaporate as it goes through the charging port.