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Registered
1999 DeVille De Elegance
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106 Posts
Discussion Starter #1
When I start my 99 Deville, Ive been getting the "Ac Low Refrigerant" message on the DID all throughout the winter. Last year I did recharge the AC with an over the counter 134a refrigerant and eveything worked perfectly all throughout the summer. Obviously there is a leak somewhere. Now that summer is here again, I expected to have to perform the same procedure to have AC for the summer....not an issue. However, when I just tested the pressure, it read a tad over 45lbs. I expected it to be much less since there is apparently a leak. Why is the pressure where it should be if there is a leak and the system is detecting a lack of refrigerant? Should I simply expell the existing pressure down to some level (25lbs?) and then refill with a new charge of 134a until the pressure is back up around 45lbs again? I am aware that the proper in shop procedure would be to recreate a vaccuum an refil, but that of course would cost $$$$ since there is an apparent leak. Easier to fix for the year for a $30 can of refrigerent which is the route I would prefer to take.
 

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98 DeVille, 97 DeVille d'Elegance
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7,345 Posts
You need a set of gauges for both high and low pressures, can o freon with gauge suck.
If you don't vacuum the system out it will not function properly.
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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26,323 Posts
:yeah:

And if that message is displaying the compressor is disabled. Static low side pressure is higher than when the compressor is running. You need to clear the code to enable it.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,265 Posts
When I start my 99 Deville, Ive been getting the "Ac Low Refrigerant" message on the DID all throughout the winter. Last year I did recharge the AC with an over the counter 134a refrigerant and eveything worked perfectly all throughout the summer. Obviously there is a leak somewhere. Now that summer is here again, I expected to have to perform the same procedure to have AC for the summer....not an issue. However, when I just tested the pressure, it read a tad over 45lbs. I expected it to be much less since there is apparently a leak. Why is the pressure where it should be if there is a leak and the system is detecting a lack of refrigerant? Should I simply expell the existing pressure down to some level (25lbs?) and then refill with a new charge of 134a until the pressure is back up around 45lbs again? I am aware that the proper in shop procedure would be to recreate a vaccuum an refil, but that of course would cost $$$$ since there is an apparent leak. Easier to fix for the year for a $30 can of refrigerent which is the route I would prefer to take.
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Why is the pressure where it should be if there is a leak
and the system is detecting a lack of refrigerant?

this is exactly why we say those single-gauge dispensing tanks are worse than useless -
and should NOT be sold over-the-counter -

don't take this the wrong way - but -

people who have no clue about AC systems -
become an expert - because "I did it last year - and it worked " -

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to answer your question -
you are looking at "static" pressure - not "working" pressure -

HUH?

when the AC system is OFF -
the high side and low side equalize -
that is STATIC PRESSURE -

typically - something above 70psi -
in a properly working system -

WORKING PRESSURES are a direct result
of ambient temperature and relative humidity -

example -
assuming 80* - 60% humidity -
temp set to 60* -
center vents selected -
blower on a medium speed -
a "perfect" working system system -
LOW pressure around 27 to 30 psi -
HIGH pressure around 175 to 200 psi -
center duct discharge air temp 39* to 42* -

------------------------
 

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1999 DeVille De Elegance
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106 Posts
Discussion Starter #5
So the static 45psi reading I am getting is 25psi below where it should be; if the static reading should be around 70psi. If memory serves, the reading was around 25psi last year before I filled it up to a 45psi reading, but I cannot say for sure. From what you state above, the only advice you can give is take it to a professional? I do have pressure guage so I can read both the low and high sides, but not simutaneously.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,265 Posts
So the static 45psi reading I am getting is 25psi below where it should be; if the static reading should be around 70psi. If memory serves, the reading was around 25psi last year before I filled it up to a 45psi reading, but I cannot say for sure. From what you state above, the only advice you can give is take it to a professional? I do have pressure guage so I can read both the low and high sides, but not simutaneously.
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So the static 45psi reading I am getting is 25psi below where it should be
the reading you are getting is the static pressure - CORRECT -

it doesn't make any difference what the actual static pressure number is -
other than it's well below the "typical" static pressure of a working system -
meaning it is low - too low to work -

From what you state above,
the only advice you can give is take it to a professional?
not necessarily -
but if you want to SAFELY work on the system yourself -
you need some basic AC "tools" -

first is a real AC gauge set -

I recommend the Mountain 8205 set - $56 - with free shipping -
http://www.amazon.com/Mountain-8205-R-134a-Manifold-Couplers/dp/B000JFHNG0
this is a high quality - but inexpensive set -
comes with nice long hoses and both HIGH and LOW side quick-connects -

you will also need a "can tap" -
Mastercool 85510 - $11 - also from amazon -

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I do have pressure guage
so I can read both the low and high sides,
but not simutaneously.

you can't imagine how much that statement scares me - :canttalk::suspense:

I don't even want to know HOW you can read both sides from one gauge -

I will tell you this - SERIOUSLY -

even with the correct tools -
AC systems are dangerous to service -
if you don't know what you're doing -

high side pressures can top 400+ psi -
open the wrong valve on a working system -
it can turn that innocent can of freon into a hand grenade -
and it WILL mess you up!
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,781 Posts
high side pressures can top 400+ psi -
open the wrong valve on a working system -
it can turn that innocent can of freon into a hand grenade -
and it WILL mess you up!
:yeah: :hide:
 
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