Correction: R134a Conversion Question (Sorry)

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richrx - 13 Aug 2007 02:40 GMT

Greetings,
Is it possible for air to blow too cold from the center vent after
converting from R-12 to R-134A? I just converted my 1993 Honda Accord.
A technician pulled as vacuum for 30', added exactly 28 oz of R-134A
(the lower limit of R-12 listed on the under hood plate) & told me
that oil would not be necessary because the car was so old that there
was probably enough mineral oil impregnated in all the parts to
maintain adequate lubrication. He said these conversions could fail
immediately, in a week or whenever. There were no guarantees. After a
few days & research, I added a can of 2 oz Ester oil with 2 oz R-134A
to give some circulating lubrication. Anyway, the vent blows at 40
degrees after a few minutes & then after I turn the fan down, it
fluctuates between 30 to 40 degrees (confirmed with 2 different
thermometers). Pressures are 35 to 40 PSI low & 230 to 280 PSI high. I
thought the system was working great until I found this quote from a
technician in an old thread (2002) in response to a poster who had
stated that his conversion was blowing ice cold:

"Then its too cold....no system puts out air at 32F and is working
normally,
unless its a refrigeration unit..:)
That would mean, the system is UNDERCHARGED....look at any refrigerant
temp/pressure chart."

He was attacking the credibility of the original poster, who seemed
knowledgeable but abrasive.

My understanding that overcharging with R-134A when converting was the
most common error. Based on my pressures & temperature results, is my
system undercharged? Is there something wrong with mys system to be
blowing cold air. It seems to be working great.
Thanks,
Rich

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C. E. White - 13 Aug 2007 13:18 GMT

You probably should check your thermometer (mix up a cup of crushed
ice and water and dunk the problem in it to make sure it is close to
correct). Hondas use an expansion valve with a thermostatic probe. You
probably need to replace the R12 valve with one intended for R134. I
also think you have too much R134 in the system. Most of the
guidelines I see say to use 65% to 75% as much R134 as was specified
for R12 when doing the conversion. I've had three systems converted to
R134 (two in farm tractors) and all worked fine. In fact, the last one
converted works better than when new.

http://www.honda-tech.com/zerothread/1665946

Ed

> Greetings,
> Is it possible for air to blow too cold from the center vent after
[quoted text clipped - 37 lines]
> Thanks,
> Rich

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richrx - 13 Aug 2007 19:56 GMT

On Aug 13, 5:18 am, "C. E. White" <cewhi...@removemindspring.com>
wrote:

> You probably should check your thermometer (mix up a cup of crushed
> ice and water and dunk the problem in it to make sure it is close to
[quoted text clipped - 51 lines]
> > Thanks,
> > Rich

Thank you for responding.
I confirmed the temperatures with a new thermometer. Maybe I will drop
both of them in ice water to verify. As far as it being over-charged,
I read on some site that a rule of thumb method when converting was to
stick a thermometer in the vent, add R-134A slowly while the
temperature drops. When the temperature starts going up again, they
advise to remove the amount of R-134A added after the temperature hit
its lowest. I would expect warmer vent temperatures & higher pressures
if I was over-charged. Also, when the tech checked out my system with
an electronic leak detector, a "medium" leak was detected around the
compressor mounting so any state of over-charging will self-correct
itself.
I was actually interested in confirmation of the statement that an
undercharged R-134A system would produce a "too cold" situation. It
seems counter intuitive.
Rich

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Steve - 13 Aug 2007 22:02 GMT

> On Aug 13, 5:18 am, "C. E. White" <cewhi...@removemindspring.com>
> wrote:
[quoted text clipped - 71 lines]
> seems counter intuitive.
> Rich

There are so many disturbing things about this conversion that I don't
know where to start.

First of all, "the parts are impregnated with enough mineral oil to
protect them" is absurd. By that theory, you should be able to drain all
the oil out of your engine and never re-fill it after 50,000 miles,
because "its got enough oil impregnated into it to protect it."

Second, adding a couple of ounces of ester oil and hoping for the best
is asinine. There is now (potentially) too much inert matter (oil) in
the system for it to work right, let alone last long. The ONLY way to
achieve a successful conversion is to completely drain the system of all
oil, FLUSH the evaporator and condensor and hoses with a solvent (but
NOT the compressor! just pour the old oil out if it), and then add the
correct amount of PAG or POE (aka "ester") oil for the system. The oil
charge for R134a is the same as it would be for R-12. You also need a
new receiver/drier whenever the system has been opened and flushed.
Replacing the drier is even more important with R-134a than with R12
because R-134a oils absorb water so easily, much like brake fluid does.

Third, the "rule of thmb" quoted above about slowly adding R-134 and
watching a thermometer is asinine. The ONLY correct way to charge a
conversion is to use 75 precent (by weight) of the recommended R-12 charge.

Fourth, whether or not an undercharge causes a "too cold" problem at the
vents depends on the design of the system. Is the thermostatic clutch
cycling switch located in the evaporator core? If so, then NO it won't
blow too cold. Is the switch located on the suction line under the hood?
If so, then MAYBE it will blow too cold becuse there's not enough
cooling potential left after the evaporator to cool down the suction line.

All in all, I'd say this conversion is marginal at best, disastrous at
worst. It is very possible and practical to convert older systems and
have them perform very well and last a very long time. I've converted
two 1960s systems of my own, and they've both performed extremely well.
But you can't scrimp- its not a simple thing to do, and saving $$ by
skipping steps like flushing out the old mineral oil is a false economy.
You run the risk of having the oil block the expansion valve causing a
cooling loss (at best) or having the compressor suck in a big slug of
un-dissolved mineral oil and break a piston or a valve (at worst). And
no matter what, the presence of the mineral oil that is not soluble in
R-134a will decrease the effectiveness of the soluble PAG or POE oil
because some of the PAG or POE will try to mix with the mineral oil and
fall out of circulation, rather than staying dissolved in the
refrigerant and circulating through the system..

Reply to this Message

Rich - 14 Aug 2007 03:11 GMT

>> On Aug 13, 5:18 am, "C. E. White" <cewhi...@removemindspring.com>
>> wrote:
[quoted text clipped - 117 lines]
> fall out of circulation, rather than staying dissolved in the
> refrigerant and circulating through the system..

Thank you for responding. All your points are well taken & previously
encountered during my research of this subject. My compressor(14 years
old) had a slight shaft oil leak & the aforementioned medium (so far the
charge has lasted 10 days) Freon leak at the mounting base/bolts. The
initial diagnosis by the independent tech was that all I needed was a
recharge with R-12 which is readily available at a reasonable price not
far from where I live (Arizona) Inasmuch as the local Honda dealer had
recommended a new compressor ($1800) & I did not want to damage the
ozone layer by just throwing R-12 into a leaky system, I opted to do a
simple retrofit to last the possible short, existing life of the
compressor. However, I have a couple of asinine follow-up questions.
Approximately what percentage of the lubricant resides in the
compressor? Does all the oil in the compressor immediately migrate from
the compressor & circulate when the compressor is on? Or does some of
the oil always remain in the compressor? If so, does any of that
resident oil passively offer lubrication to the compressor through
simple mechanical action of the compressor?
By the way, I became asinine when I read the following on the
Interdynamics site:

"Do I need to remove the oil that's in the system? Is the old oil
compatible with the new oil?

No. The residual mineral oil left behind after you evacuate a R-12
system will not mix with the new R-134a refrigerant. That is why we add
Ester Oil, because it will mix with R-134a, lubricate the system
components and is compatible with the residual Mineral oil..."

Their kit would have added approximately 7 to 8.5 oz of Esther oil
depending on whether I used pre-mixed R-134A or added the recommended
amount separately. So, I chose the safe first step of being 23 to 28% as
asinine as Interdynamics by adding only 2 oz of Esther oil.
Furthermore, also from the Interdynamics site, this is what I was
planning to do:

"...The mineral oil just collects in a low place in the system (such as
the accumulator), where it stays, UNTIL IT IS REMOVED AT SOME LATER DATE
DURING FUTURE MAINTENANCE OR REPAIR (my emphasis). The mineral oil does
no good, but it does no harm either. It's just there."

Thank you,
Rich

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Kevin Bottorff - 14 Aug 2007 14:41 GMT

>>> On Aug 13, 5:18 am, "C. E. White" <cewhi...@removemindspring.com>
>>> wrote:
[quoted text clipped - 167 lines]
> Thank you,
> Rich

that is not necessarly true as oil has been know to pool in a poor spot
and restrict flow where it shouldn`t. KB

Signature

Thunder Snake #9
"Protect" your rights or "lose" them.

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Steve - 15 Aug 2007 03:57 GMT

However, I have a couple of asinine follow-up questions.

> Approximately what percentage of the lubricant resides in the
> compressor? Does all the oil in the compressor immediately migrate from
> the compressor & circulate when the compressor is on? Or does some of
> the oil always remain in the compressor? If so, does any of that
> resident oil passively offer lubrication to the compressor through
> simple mechanical action of the compressor?

Actually that's NOT a simple question. It depends not only on the type
of compressor (some have large oil sumps that tend to retain a fair
amount of oil, some don't, some have oil cirulating pumps, some don't),
but also on how the system is operating. When the system first kicks on,
the oil in the suction side plumbing (everything between the expansion
valve and the suction inlet of the compressor, including the evaporator)
foams up like whipped cream as it is subjected to vacuum and all the
refrigerant that is dissolved in it flahes to gas. When that happens, it
passes through the compressor and some will accumulate in the sump (if
so equipped), but some will also go right through and get into the
discharge side, where it slowly works its way back around. In general,
the oil goes nuts for the first few seconds after the system cycles on,
and then tends to stabilize with a certain fraction in the compressor
sump and oil circulation system, and the rest distributed and
circulating with refrigerant. When measuring the oil in a system, you
are supposed to operate it for 5-10 minutes at high idle and high fan
speed (max load on the A/C) to stabilize the distribution of the oil. Of
course, you generally only DO that if the system is broken, in which
case you can't run it... but I digress. Lots and lots of really
short-cyling can be very hard on the compressor because that tends to
put ALL of its oil out in the refrigerant stream, but that's not usually
a problem with car A/C systems as much as home systems where there's a
long run of plumbing between the compressor unit and the air handler.

> By the way, I became asinine when I read the following on the
> Interdynamics site:

Interdynamics .... oh joy. :-p

> "...The mineral oil just collects in a low place in the system (such as
> the accumulator), where it stays, UNTIL IT IS REMOVED AT SOME LATER DATE
> DURING FUTURE MAINTENANCE OR REPAIR (my emphasis). The mineral oil does
> no good, but it does no harm either. It's just there."

But it takes up space that the engineers who DESIGNED the system
intended to be occupied by refrigerant.... not oil. It does have
negative effects, and if a good bump in the road causes a slug of it to
fly into the suction side of the compressor, the effects can be sudden,
loud, and destructive :-p

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