[DML] Re: Advice on AC lines
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[DML] Re: Advice on AC lines

If your external surface temps are below 32 degrees, the likely
culprit is your low side pressure switch. The Delorean cycles its
compressor on and off to meter freon into the evaporator. 

Because R134 doesn't contain chlorine, the drier doesn't seem as
critical to me. The old R12 would react with moisture to create acid
that would eventually eat through the thin walled metal components. Of
course the boiling point of R134 is below 32 degrees, so you do need
to ensure that there's no moisture in the system (otherwise it will
ice up internally). My experience has been that trying to remove
components from 30 plus year old A/C systems usually causes more
problems than leaving the components in place (with the notable
exception of the compressor, which is designed to be removed). The
metal used is *VERY* thin. You can easily kink and bend it trying to
free the rusty old nuts (the way I see it, if the fittings are that
rusted together, there's no need for O rings anyway!). I have systems
that leak freon, and the cheapest and easiest solution is just to top
them off as necessary (BTW: R134 is the exact same stuff used in those
Dust-Off keyboard cleaners -- I don't see any difference in my little
leaks and everyone else spraying their computers). As long as the
system doesn't leak below atmospheric pressure you don't even need to
pull a new vacuum.

Regarding oil: The two most common R134 oils over here are PAG and
Ester. Because it is mineral based, Ester oil mixes better with
however much R12 oil happens to be in the system (I've converted some
of my cars with the old compressor and oil in place, with identical
results to a new compressor & oil). People tend to go crazy with oil
anyway. Remember: oil is there for the benefit of the compressor.
Because it doesn't evaporate, too much oil elsewhere will gum up the
works. I've had to blow out evaporators when they were full of oil and
the freon couldn't get in to evaporate. Those cans of oil designed for
the low side port are particularly insideous -- a nice idea, but most
of the oil ends up in the evaporator. An A/C compressor only needs a
couple of ounces anyway. Because condensors work the other way around
(from the top down) oil won't bother them.  Oil doesn't evaporate when
pulling a vacuum either -- if the system has too much you need to blow
it out (the compressor itself can be removed and tipped upside down).

Most flushing fluids are mineral based (I've been advised to use plain
old paint thinner). Even though flushing fluid will evaporate when
pulling a vacuum, I can't help but think that some of it ends up left
behind in the accumulator, absorbed into the hoses, etc. Ester oil
will of course react better with residual flushing fluid. 

"Stop up" products of any sort (radiator, transmission, etc) usually
cause more problems than they cure. Because they circulate throughout
the whole system, they gum up things you don't want stopped up. The
only product I've ever seen suitable for such are the tubes of
aluminum powder that parts houses used to sell for cooling systems,
and even it would accumulate in/under the radiator cap.

Bill Robertson

>--- In dmcnews@xxxxxxxxxxxxxxx, "Kevin Milliken" <kevin.milliken@...>
> If you are changing from R12 to R134a
> Option 1
> I have just been through this loop in the UK, after talking to
> quite a few A/C guys and manufacturers the correct thing to do is
> all the flexible
> hoses which has now been done on one delorean. THE MOST important
item to
> change is the drier under
> the front wheel arch, If you dont you are asking for problems, it is
> "supposed" to be changed
> every two years but if it is running o/k on R12 and are notchanging
from R12
> to R134A.then leave it.
> The result of this is R134A  A/C running at 3.8 degrees out of the
vents and
> the doors now freeze on the outside.
> Option 2
> If your hoses are o/k then change the drier as above, then have your
a/c man
> use the new R134a oil
> which is used when changing from R12 to R134A (this oil is very, very
> expensive about £50.00 per half pint
> about $100.00) it is not the normal R134A oil. This is used to
lubricate the
> pump and coat the inside of the
> hoses. DO NOT under any circumstances let your a/c man use a sealer
> compound. This will wreck your a/c
> if you have a problem later. Sealer compound is designed to be used
on old
> cars which need a quick fix
> and will be sent to the breakers yard after a year or so, even the
> manufacturers of the sealers say dont use
> it.
> I have gone through Option 1 and about to go though Option 2 on another
> Delorean
> If you need any other info let me know.
> Kevin
> #5959
> #10163

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