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[x25xe]

But the receiver / dryer should be removing any moisture in the refrigerant.  If it is not, then it needs replacing - all this of course assumes that there is moisture in the refrigerant.  Could also be the expansion valve at fault.

[cdx25]

Hi there,

>> when the system is running the low side pressure as measured with a Halfords gauge is in the right ball park

My experience is that gauge pressure will show you pressure even when the system is quite low on charge.  Vapour pressure isnt like air in a tyre, because you have liquid in the system too.  This liquid refrigerant boils off to produce gas pressure.  The pressure you get is then a function of temperature - ie hotter = more pressure.  (So low pressure on a static gauge means a real low AC charge.)

(Someone who knows more about gas theory will be able to explain vapour pressure better Im sure!)

>>I haven't added any refrigerant, but the cooling performance is pretty weak.

Many causes but most likely is that the gas has escaped over time and you are low on charge.  If you get *some* cooling then that suggests that the system is basically OK (although it might be in poor condition)

>> When you first start the system the high side connection from the compressor gets hot immediately and the low side gets cold but after a minute or two  they're warm to the touch and cool to the touch respectively. Makes me wonder if it's icing up internally due to moisture in the refrigerant?

More explainable by a low charge I would guess.

Best thing is to have it vac'd down and refilled (make sure you pull a good vacuum for enough time for any moisture present to boil off).  A good micron gauge is needed for this bit, vac gauges are not accurate at very low pressures.

Alternative solution is to just add a tin of gas in with an adaptor via the low side (charging with gas only, i.e. dont turn the can upside down) but this is a bit of a bodge because a) no idea how much is in there already and b) you often cant empty the lines of air before you start to charge, meaning there is a risk of moisture going in too.  Having said that there are a lot of people who top up this way - your mileage may vary!

Hope this helps,

Jon

[x25xe]

How long should a system have a vacuum on it prior to a refill with gas and lube?  I was always under the impression that the longer the better but have since been advised that this is not the case.  Which is correct?

I also agree with you about the cans of gas available at Halfords etc.  I always advise people against using these for the reasons that you have stated.

[Kevin Wood]

Thanks for the information. I can see the problem of simply measuring pressure when you're dealing with a system with vapours and liquids in different proportions!

Sounds like it needs a proper service as you say but it's nice to know a little about what's involved beforehand to avoid being fobbed off!

Cheers,

Kevin

[cdx25]

>> Sounds like it needs a proper service as you say but it's nice to know a little about what's involved beforehand to avoid being fobbed off!

and other post:

>> I also agree with you about the cans of gas available at Halfords etc.  I always advise people against using these for the reasons that you have stated.

I think the thing that would clinch it for me is that the halfords topup will be 30 quid (and every likelihood is that just one 300g tin isnt enough - my recharge weight on my Omega was 950g or so off the top of my head).  Compare this to a vac down, recharge with the correct amount plus maybe dye costing 50quid or thereabouts - its worth the extra.


>> How long should a system have a vacuum on it prior to a refill with gas and lube?  I was always under the impression that the longer the better but have since been advised that this is not the case.  Which is correct?

Hmm, the answer to that all depends on 1) if moisture is present as this takes time to come out of the system and 2) if you have a decent enough gauge to know when you have reached the end point.

1) A good level of vacuum takes time to reach, even with a decent vac pump with new pump oil.
2) Boiling point of water reduces as pressure reduces (table in link below)
3) Water in the system then starts to boil off at the low pressure
4) But this takes time to boil off and be pulled out of the system.
(Long pipes and slow moving molecules!)
5) Water presence & boiling off indicated by a long time to reach a good vac level
(A leak is indicated by an inability to hold that vac level with the pump isolated)

If you DONT have a micron level gauge then I'd say that in general longer is better...  Most people will accept something between 20-40 mins as being about right, but this figure depends on how long it takes to boil off and pull out any water.  Shouldnt be much water there unless the rec/dryer is saturated.

Better is to use a Micron level gauge so you know when to stop!  (Which may be why some people say that longer isnt always better - and with the right kit this is true.)

From Robinair (Auto vac pump site) http://www.robinair.com/acsolutions/acvacuum/acvacuum.php

"best way to know for sure that the system has been thoroughly dehydrated is by using a thermistor vacuum gauge. This prevents wasting time by pulling down after evacuation is complete or risking inadequate dehydration"

On my car with no commercial pressures of time?  I would wait until I reached max reachable vacuum on the micron gauge (indicating all water boiled off) and if that value was acceptable - I'd then hold that for about 10 minutes to be sure.  This would take say 30-45 minutes on the pump in all if the system was generally OK.

Hope this helps,

Jon

[The Barge Captain]

Question.  If doing a propper job, a vacuum pump is connected to the system, and is unable to create any decent vacuum after a reasonable time, this should indicate a leak in the system somewhere right? so therefore any problem on that side of things should be detected before wasting time and money putting gas into the system.
Where is the dryer on the omega, and is it a part i can change myself without breaking into the system? I'm guessing not.  Anybody know what a replacement is likely to cost?

[cdx25]

>> If doing a propper job, a vacuum pump is connected to the system, and is unable to create any decent vacuum after a reasonable time, this should indicate a leak in the system somewhere right?

Correct.

>> so therefore any problem on that side of things should be detected before wasting time and money putting gas into the system.

Yep - or $$$ wasted

>> Where is the dryer on the omega

Dont know offhand as Im new to this model and havent got my car handy to look at.    Anyone else know?

>> is it a part i can change myself without breaking into the system?

No - soon as you remove it you will open the entire system to air and that means get a new rec/dryer in quick and then vac down to remove moisture before recharging.

Jon

[x25xe]

Hi Jon

Thanks for your replies - all very informative.  I will take a look at the link your provided.  I have an interest in A/C systems in cars and my first car with A/C cost me £1000 to repair (this was in 1999) this was on my Cavalier which I still have and the A/C still works as I have it re gassed and a new receiver / dryer every 2 years.  Has worked for me which I why I recommend the same to others.

[The Barge Captain]

You sound like a man who knows what he is talking about.  I would come to see you for my aircon, but it would take me half a day traveling there and back and cost £30 in fuel just to get the bonnet open  
Guess i'll just have to go local, but thanks for the information provided mate.

[cdx25]

No worries - its nice to be able to contribute back something to the forum in an area I can help with.  Hope the regas goes OK.  Shout if I can help in any way more.

Jon

[gofwb]

I have been wanting a regas on my 02 2.6 for a while and was pleased to discover that Kwikfit did it as they are just across the road from where I work, 1.30pm yesterday gave them a ring, they said "bring it straight round as we don’t have much work on", dropped it off, they said "it would take about 30mins", I said I would pick the car up about 3.10pm.

Went back to work then went back at 3.10 to see them still working on it (alarm bells rang) manager says "its taking a bit longer than usual as we have to remove all the old refrigerant", I say "that’s what you are supposed to do anyway",  manager looks a bit grumpy and goes back to the other 3 "Mechanics" who are all peering under the bonnet and at the regas machine, manager comes back and says we cant regas it as the compressor does not work.

I go to talk to "mechanic" who tells a different story that "the machine will not fill it up” they have rang the machine manufacturer who insists that they are doing everything correct, I say you need the air con running for the regas don’t you" “yes” says the "mechanic". "Well you won’t get it on with the "ECO" switch on, "mechanic" says "he did not know anything about that".

They must have managed to get a little bit of gas in as the compressor clutch works now.

So if you take it to Kwikfit tell them "Don’t touch the bloody ECO button!!”

I dropped it off this morning and pick it up this afternoon will give you the verdict on them tomorrow.

Frank.

[Bo Bo]

You can't get better than a..........  

[Kevin Wood]

Sounds like they're about as good at aircon as they are at suspension geometry.

Surely during lesson one of the thick-fit air con training course it would have explained how to turn the air con on in the first place.

Kevin

[Jimbob]

they have probably tried to turn it on, not realising it is always on in an omega and you have to turn it off if you dont want it.

Dont they fill you with confidence!

[Bo Bo]

Well I'm off to them in about 1/2hr but I won't be leaving mine & I'll make sure they know about the ECO, not that ever use it.....