What Variables Affect Rate at Which Refrigerant Escapes System? - PeachParts Mercedes-Benz Forum

shertex · #1 03-03-2011, 09:21 AM

Both of my 300's have slow refrigerant leaks; both are R134a. If memory serves, last summer I had to add refrigerant every two months or so to each to change the system from cool air to cold air. Last time I added refrigerant was in August. So I was a bit surprised, now in early March, to find that both systems are blowing ice cold. So, obviously, the rate of loss has decreased.

So could some of you help me understand what the variables are? I can think of various factors: where the leak is, ambient temp, extent to which AC is being used, hoses swelling/contracting come to mind. What variable(s) most likely account for the slowing of the rate of refrigerant loss?

Thanks.

layback40 · #2 03-03-2011, 09:30 AM

The size of the hole & the pressure behind it are the 2 factors.

shertex · #3 03-03-2011, 09:46 AM

Quote:

Originally Posted by layback40

The size of the hole & the pressure behind it are the 2 factors.

Since hole sizes don't shrink, that leaves pressure. So what affects the pressure and to what extent? I assume the only two variables here are ambient temp and whether or not the system is being used. And of course the quantity of refrigerant.

showme · #4 03-03-2011, 10:56 AM

O ring conditions are critical.

moon161 · #5 03-03-2011, 11:34 AM

Some refrigerant top-up cans come with sealant, IIRC. May have sealed the crack. Really the way to tell is tracking system pressure over time. Ice cold AC in march doesn't say much unless you live in AZ.

leathermang · #6 03-03-2011, 12:05 PM

Quote:

Originally Posted by shertex

Since hole sizes don't shrink, that leaves pressure. So what affects the pressure and to what extent? I assume the only two variables here are ambient temp and whether or not the system is being used. And of course the quantity of refrigerant.

The pressure is going to be affected by which side of the system the leak is on... high or low... there is probably a ' high side cut off switch ' which should limit the high side pressure .... obviously.....
So the time you are running the system and the side the leak is on are major factors...
Have you tried just ' snugging' up all the o ring joints you can reach ? ( use two wrenches and what are called ' line wrenches ' to do this safely...

ah-kay · #7 03-03-2011, 08:47 PM

Quote:

Originally Posted by layback40

The size of the hole & the pressure behind it are the 2 factors.

I like it, right on the nail.

It is natural for the A/C to leak a little over time, it is just a matter of how little. I read it somewhere that you lose about 1-2oz per year.

bobodaclown · #8 03-03-2011, 05:05 PM

The need of the A/C. The more you need it the quicker it will leak out.

vstech · #9 03-03-2011, 07:47 PM

many variables of operation influence the leak rates in a system, where it's leaking, how big the leak is, temp on the line, as parts expand, holes get larger/smaller. seals pliable in summer heat, will tighten up in winter. pressure lines leaking while system is running, will only have vapor at low pressure in winter, where in summer it will have liquid under high pressure. liquid contains 30,000 times more molecules in the same volume as a gas at the same pressure...

layback40 · #10 03-03-2011, 09:30 PM

I wasnt trying to be a smart @SS with my post.
When the air con parts are cold in the winter & not in use, pressure equalizes & is generally lower except in the cold side of the system. When you use the air con the compressor warms up & is at a higher pressure on the hp side. Things expand & this could cause the leak to get smaller or larger. You need to run the air con now & again in the winter to keep the compressor seal from deteriorating.
A good detector is the best way to find leaks.

vstech · #11 03-04-2011, 02:27 AM

for a good detector, ultrasonic is the best!

layback40 · #12 03-04-2011, 09:44 AM

Quote:

Originally Posted by vstech

for a good detector, ultrasonic is the best!

I would have thought a haylon detector is what you would go for. How does the ultrasonic detector work John? I am probably 20 years out of date!! Where the heck is Larry Bible when you need him!!!

leathermang · #13 03-04-2011, 10:54 AM

Quote:

Originally Posted by vstech

for a good detector, ultrasonic is the best!

Is ultrasonic the brand name or the way in which it works... like some cleaning systems ?

Rooster300SD · #14 03-04-2011, 11:03 AM

IIRC, 134a is a smaller molecule than R12.
So, all things being equal, the 134a will leak out sooner.

Jeff

leathermang · #15 03-04-2011, 12:51 PM

Quote:

Originally Posted by Rooster300SD

IIRC, 134a is a smaller molecule than R12.
So, all things being equal, the 134a will leak out sooner.Jeff

That is also one of the drawbacks to using ANY BLEND.... the part of the blend which is smaller molecules do tend to escape at a different rate than they exist in the mix..
Thus, if you get a little low... and need to top off... as you could do with 134a or R12... you instead need to take out everything and reinstall the blend...

Some of you are thinking ' if you are getting low you have a leak and need to fix it' BUT our compressors are designed with a ' leak' on the front of the main shaft to bring lubricant to that front seal... thus your system can be ' perfect' and still need.... after several years... a little more refrigerant... not much or very fast. that would be a leak... but you can just need topping off every few years with a completely sealed system...