1978 460cui with A/C

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Steph - 03 Jul 2006 16:26 GMT

I a have 1978 clubwagon E-250 with the 460 and dual zone A/C.
What is involved in retrofitting the A/C with 134a refrigerant?

Is the valve on the curved tube just to the right of the compressor the low
pressure fitting, or a high pressure fitting?

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TM - 03 Jul 2006 18:05 GMT

Large Hose going into aluminum accumulator is the low side pressure fitting.
Smaller Hose with smaller pressure fitting is the high side.

Retrofitting the air conditioner will require changing the oil in the
compressor case, for best results do a nitrogen purge on the system to
remove any residual r-12 remnants. I usually replace the compressor due to
age and not having to crack the system back open again. The thermostatic
expansion valve (TXV) or metering tube will have to be replaced due to
different pressure tolerances between R-12 and R-134a. I would also replace
ALL of the rubber o-rings while the system is depressurized. Lastly pull a
vacuum on the system, I usually leave the vacuum pump running for about 30
minutes. Check for leaks by stopping the vacuum pump and closing all
valves. If the vacuum does not drop at all after 5 minutes, you are ready
to charge the system, make sure you purge the air from the hose lines.
Don't forget to install the retrofit low side fittings before pulling the
vacuum.

As far as the fitting on the tube, you must compare fitting sizes the larger
one is the high side.

Any questions, email me direct, just remove the extra dot com.

TM

> I a have 1978 clubwagon E-250 with the 460 and dual zone A/C.
> What is involved in retrofitting the A/C with 134a refrigerant?
>
> Is the valve on the curved tube just to the right of the compressor the low
> pressure fitting, or a high pressure fitting?

Reply to this Message

SnoMan - 03 Jul 2006 18:51 GMT

>Large Hose going into aluminum accumulator is the low side pressure fitting.
>Smaller Hose with smaller pressure fitting is the high side.
>
>Retrofitting the air conditioner will require changing the oil in the
>compressor case, for best results do a nitrogen purge on the system to
>remove any residual r-12 remnants.

This is a wasted effort, a good vacum will remove it.

> I usually replace the compressor due to
>age and not having to crack the system back open again. The thermostatic
>expansion valve (TXV) or metering tube will have to be replaced due to
>different pressure tolerances between R-12 and R-134a.

THe p[roblem with this is that it changes the flow rate and prusse
curve for compressor if you change orfice size. All though the logic
is good, the possible side effects are not.

> I would also replace
>ALL of the rubber o-rings while the system is depressurized. Lastly pull a
[quoted text clipped - 4 lines]
>Don't forget to install the retrofit low side fittings before pulling the
>vacuum.

Another danger here is that R134a is not compatable with mineral oil
so some extra PAG oil has to be added to system to bind mineral oil to
pag and pag to R134a to move it through system and it can reduce
cooling some if too much is added and increase head pressure and
reduce compressor life too. ALso given age of vehcile, you should
replace recv/dryer and precharge it with PAG as this will let you ad
PAG to system without over charging it with oil

When this is all said and done, there will be a lose of cooling
capacity because R134a has about 16% less heat capacity than R12 when
it is expanded and cooled. R134a systems have larger condensors and
evapotars and different compressors and flow rates to help minimize
this effect but a lot of time R134 is a R12 systems can provide
marginal results especailly if system was not the great on R12 to
begin with.

>As far as the fitting on the tube, you must compare fitting sizes the larger
>one is the high side.
[quoted text clipped - 9 lines]
>low
>> pressure fitting, or a high pressure fitting?

-----------------
The SnoMan
www.thesnoman.com

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TM - 04 Jul 2006 02:24 GMT

Just how many retrofits have you done Mr Sno Man? I have over 100 under my
belt with a less than 5% failure rate. 90% of the failures are a result of
marginal parts not being replaced according to my recommendation.

Additional information embedded.

> >Large Hose going into aluminum accumulator is the low side pressure fitting.
> >Smaller Hose with smaller pressure fitting is the high side.
[quoted text clipped - 4 lines]
>
> This is a wasted effort, a good vacum will remove it.

Only if the system has been sealed, hasn't leaked down or succumbed to
compressor failure.

> > I usually replace the compressor due to
> >age and not having to crack the system back open again. The thermostatic
[quoted text clipped - 4 lines]
> curve for compressor if you change orfice size. All though the logic
> is good, the possible side effects are not.

The manufacturer of the refrigerant and automobile manufacturers recommend
changing the orifice tube. Thereagain, how many retrofits do you have under
your belt? I will not waste my time going into specific weights and
solubility and long term longevity should best practices not be observed.
Sure you can cut corners if you are short on cash, but it will be more
costly in the long run.

> > I would also replace
> >ALL of the rubber o-rings while the system is depressurized. Lastly pull a
[quoted text clipped - 12 lines]
> replace recv/dryer and precharge it with PAG as this will let you ad
> PAG to system without over charging it with oil

That was addressed with the changing of the oil. By the given age of the
vehicle I would replace the compressor as a matter of principle if it has
never been replaced. Compressor manufacturer warranties require you to
change the accumulator/receiver/dryer or the warranty is void.

> When this is all said and done, there will be a lose of cooling
> capacity because R134a has about 16% less heat capacity than R12 when
[quoted text clipped - 3 lines]
> marginal results especailly if system was not the great on R12 to
> begin with.

That is precisely the reason the TXV/orifice tube must be replaced or your
results will be horrid at idle.

There should be two orifice tubes or TXV's on this particular vehicle
according to the service manual more likely the latter.

> >As far as the fitting on the tube, you must compare fitting sizes the larger
> >one is the high side.
[quoted text clipped - 13 lines]
> The SnoMan
> www.thesnoman.com

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SnoMan - 04 Jul 2006 04:04 GMT

I would not brag about a 5% failure rate, 0% is a lot more impressive.
When you change the flow rate as you suggest, with a larger orfice for
R134 you change pressure curve and drop accross it since compressor is
the same. Using R134 is a R12 system is a bandaid fix at best and
there are other options out there that will cool better than R134 in a
R12 system and do not require different oil because of incompatabilty
with mineral oil like R134 is. Nothing is gained with your purge
except maybe something to charge for if you do it for a fee. You could
purge it with air if you really feel the need to since it is 79%
nitrogen anyway. A good vacum held for a while will remove old freon
and moisture but I would change recv/dryer which shold be done here
which you fail to mention which casts doubt on your methods. Besides,
you do know that R134a is VERY poisonous and that it too will be
banned in 2012 too? Replace a banned refrigerant with another soon to
be banned one (that is inferior in performance to in a R12 system),
Not very wise. Also PAG oil is glycol based so corrosion is a bigger
potenail problem in a converter R12 system and that is why you change
the drier. (mineral oil in R12 system does not react much with moistur
(not like R134a and PAG oil does anyway)

>Just how many retrofits have you done Mr Sno Man? I have over 100 under my
>belt with a less than 5% failure rate. 90% of the failures are a result of
[quoted text clipped - 88 lines]
>> The SnoMan
>> www.thesnoman.com

-----------------
The SnoMan
www.thesnoman.com

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