another a/c question

I have a 1996 Caravan 3.3L and would like to know what the capacity of
the a/c system is. I believe that I am low on R134a chemical. I would
also like to know a simple procedure. Can I tell if it is low simply by
measuring the pressure on the low side? What should the pressure be on a
fully charged system? I have a pressure gauge and fitting and have
checked it to be less than 40 lbs. By comparison my 96 Intrepid with a
3.3 engine measures 80 lbs, whether the gauge is coorect or not I am
just using it as a comparison Both measured with the engine off.

Thanks,

 

The aftermarket consumer re-charge products (Interdynamics) claim that
you can tell from just the low-side pressure (with temperature
correction needed *only* if the ambient is outside some range -
something like 70 to 80°F, IIRC), even though the shop manual procedure
uses hi-side pressure and temperature of the metal line coming out of
the condensor (a temp/pressure chart is provided with a narrow band of
acceptable operation shaded in).

I just went thru this mind game recently on my '99 Concorde, and decided
not to trust the aftermarket approximations (I don't want to be penny
wise and pound foolish) - bought a real dual gage set just yesterday at
Advance ($74). Will be checking charge level and topping it off this
weekend.

If an expert on the subject (of which I am not) posts that the low-side
method is acceptable, then by all means go with that.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')

 

This information is available right under the hood, on a label on the
radiator support panel or on the A/C compressor itself.

Pressures measured with the engine off are meaningless.

 

The easiest way to tell if you are low on refrigerant is to drive the
vehicle with
the A/C on AND IN RECIRCULATING MODE during a hot day for an hour,
then check to see that there is condensate
water coming out of the evaporator drain. If the evaporator isn't getting
cold enough
for water to condense on it, then fall into the evap tray and run out the
drain, then
it's not cold enough. The human body dumps enough water into the air for
this test to work even if your in a very dry environment.

In a damp environment, such as here in Portland, on a warm day I can turn on
the A/C at idle and within a minute, the underhood low pressure refrigerant
fittings are wet with condensation.

Ted

 

that may even be better than a a/c system performance test

 

You have to measure both the high-side pressure AND the condensor
temperature, and then look up the correct pressure for the corresponding
temperature. The procedure and chart of pressure vs. temp showing the
undercharged/normal/overcharged regions are in the factory service manual.

 

Steve - Do you (or anyone else) have any definite knowledge of how close
the cheapy aftermarket method of measuring (only) low-side pressure is
to the (assumed to be much more accurate) shop manual procedure based on
hi-side pressure and condensor temp? (I did notice in the aftermarket
"simplified" method that they do say that it is acceptable without any
temperature correction for a range of ambient temperature (something
like a range of 70 to 80°F IIRC.) (I had bought the cheapy kit for
low-side pressure only, but took it back for a refund before using it
and got a real set of gages after thinking about it. Borrowed a digital
contact temp. probe from work and topped off my system yesterday and it
works great - hopefully whatever had leaked out was *very* slowly over a
period of years vs. recent larger leak development - time will tell - I
put in 134a laced with UV dye just in case.)

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')

 

I really don't have any hard data as to the relative accuracy of the
low-side only method, but my guess is that its "pretty inaccurate." The
reason I say that is that an error of one PSI out of 30-40 psi is a much
bigger percentage than an error of 1 PSI out of 200 PSI. The high side
just gives you a lot better resolution on the measurement, so to speak.

 

Bill, I'm not a fan of the temperature test except as a quick check, to be
honest.
I prefer the method of sucking all the refrigerant out, then adding the
exact number
of pounds or ounces of refrigerant that are called for by the specs. Also,
if you
are working with a R12<->R134a conversion, the factory-supplied table is
for R12 and is useless.

However, one big problem with only measuring the low side is that if there's
a
problem in the system like a blockage that might be creating excessivly high
side pressures you won't see them.

Nevertheless I did buy one of those quick "tire checking like" A/C guages,
the
ones with the green/blue/red areas on the guage, just to see how horrible it
was.

With my 1984 Chevy, R134a conversion, filled with exactly the number of
ounces of
refrigerant called for by the specs, I checked the pressure on the quick
check guage and
was interested to note that the needle on the quick check guage was at the
absolute
minimum pressure for an acceptable system. Since the guage doesen't even
register with
less than 2 ounces of refrigerant in the system, I have to conclude that
this guage
reads low.

Ted

 

Steve wrote: "I have a 1996 Caravan 3.3L and would like to know what the
capacity of the a/c system is. I believe that I am low on R134a chemical. I
would also like to know a simple procedure. Can I tell if it is low simply
by measuring the pressure on the low side? What should the pressure be on a
fully charged system? I have a pressure gauge and fitting and have checked
it to be less than 40 lbs. By comparison my 96 Intrepid with a 3.3 engine
measures 80 lbs, whether the gauge is coorect or not I am just using it as a
comparison Both measured with the engine off."

Try here http://www.ackits.com/index.cfm?fuseaction=Chart

Sarge

 

Thanks, Ted. Kind of as I expected. I think I'll stick with the "real"
gages and the shop manual method of charging/checking. So far, after
topping the system off, my stystem is still performing well at 36°F
(recirc) and 40°F (non-recirc) at the vents with all controls max'ed. I
hope that continues (i.e., no leaks - especialy in the evaporator which
the LH cars tend to have and cost a bunch of labor to replace).

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')

 

Oh - and I did put in UV dye - just in case.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')