R129 - Aircon recharge

[LeaUK]

Hi all

This is probably quite a generic question but anyway. I'm, thinking of recharging the aircon system (probably hasn't been done for 4 years or so) and have heard that the aircon system oil must be measured, drained and the correct volume replaced - alongside the gas of course.

I'm a person who likes things done correctly, so when I talk with the 'aircon man', what are the pertinent questions I should ask regarding his practise?

Maybe someone understands what's exactly required and how it's achieved and could point me in the right direction?


Thanks
Lea

[LeaUK]

OK, here's some useful info from documentation:

129 up to 31.5.96 (and probably the the majority of R129s

Capacity:
Gas R12 1100g/R134 U 950g gas type is marked on 'filling plate'

Inspection:

1. Clean inspection glass on receiver/drier
2. Disconnect cable from pressure switch (sits adjacent to drier)
3. Start engine and idle
4. Switch air-con on to defrosting
5. Short circuit pressure switch
6. Observe inspection glass of drier. Refrigerant must increase slowly and flow bubble free - do not test above 35degC

Regarding the replacement of oil:

If refrigerant has slowly leaked out over time and requires >400g replacement replace fluid reservoir and add 20cm3 compressor oil. No oil is required if <400g.

[LeaUK]

My previous article isn't strictly true as you must measure not only the gas but any oil that comes out before the recharge. This amount of oil must be replenished in addition to any further oil being replaced.

[JimF]

Originally Posted by LeaUK

I'm, thinking of recharging the aircon system (probably hasn't been done for 4 years or so) and have heard that the aircon system oil must be measured, drained and the correct volume replaced - alongside the gas of course.
Thanks
Lea

. . why?? Is the R134 low?? Do you see lots of bubbles in the site glass when a/c in on?? Have you done the operating checks in MENU#15 to see what the temps and pressures are?

I'm sure you have read my 'disaster' about 'doing it right', in MENU#16 and look where that got me.

I must be ok because you haven't 're-charged' in 4 years, so why know??

[LeaUK]

Hi Jim

Thanks for the web site reminder, but unfortunately my A/C control panel has no digital display and therefore the diagnostics available for the 140 and the majority of 129s is not available.

Regarding your story, this is unfortunately typical of the DIY'er without access to correct data - in essence there are circumstances which oil must be added above what has been measured upon discharge. And of course oil MUST be measured and replenished upon each recharge - this is noted in MB data. I feel for you, especially as you wanted to di it 'properly'.

You mention that yours was down by a lb, well that's over the 400g which is the 'add more oil' point in the MB data. It notes that if there has been a slow leak one can assume oil loss and so additional oil to that measured on reclaim must be added. I'm surprised the W140 isn't similar?

In the UK we have automated 'A/C' recharge systems. These measure the volume of gas discharged alongside the volume of oil removed. Therefore they can calculate the exact replacement oil volume. Gas is replaced to manufacturers specs.

Also, the 119 engine requires additional oil volume replacement depending on the A/C component replaced, so this info is great to know. I only use MB reference data as this is what the dealer workshops refer to and hopefully it's accurate but of course it's not always guaranteed.

My system is probably operating ok but MB specify checks every 2 years or 20km; I've owned mine for three years now but two years previous the car went unserviced (very low mileage in this period). So I think it's time for a complete recharge then I can be sure of a datum.

Top-ups aren't recommended, so it's the full treatment for mine - like you I want it carried out correctly, hence my post here and lots of reading. However I take your warning, but assuming if the correct kit is used alongside MB documentation it should be fine...

'cross-fingers'

Cheers
Lea

[JimF]

recycling systems here; one of the pictures (Menu#15) shows the 'Cornwall' (built by RobinAir) R134A system. It separates the oil from the refrigerant and shows how much was recovered by weight. All recycling systems use 'weight' not volume.

All I can say, if oil is removed, it MUST be replaced. Doing what I did for four (4) complete cycles, shows how you can kill a compressor quickly!

But I also say that common sense should be used: If you checked you a/c system when it was operating ok, and at that time, saw the you had no 'bubbles' in the site glass, and NOW see a SOME bubbles, you can safely conclude that some has escaped. Not very much, but some.

Now should you re-capture it all - or - simply add an amount of refrigerant that will cause the bubbles to disappear. Personnally, I will do this procedure FIRST, EVERY time! As you probably know you can get R134A w/ oil if that is a concern.

Yes, I agree that in order to "know" exactly how much the system is down, you need to re-capture it ALL. That's the right way. Be interested in what you find.

[LeaUK]

I've just started looking into AC systems and so I've never checked the system for 'bubbles' previously so I simply have no base line - hence the full recharge option to create a baseline.

Weight - uhm, I haven't seen the AC system yet so am only going by MB data. MB quotes volume, never weight...

I'll let you know how it turns out.

Lea