BarryBum

Is there a trick or special way or type of Freon I need to add to my 2000 C5 or is it just R13 and the old timey way of adding it?

lucky131969

If by the "old timey way", you mean evaluating the system pressure with gauges per the manual, and adding freon as required, then no.......no special trick.

BarryBum

my bad........the politically correct version is R134a.

BarryBum

Yep, thats what I meant by "old timey"

dougbfresh

Well the CORRECT way is to evacuate the system (with an approved system), see if it holds a vacuum (leak test) then refill with the correct amount of CORRECT refrigerant.

Since you can't directly tell how much refrigerant is in the system after the fact all you can do is read the high and low pressure sides and "guesstimate" how low you might be. The cheapy stuff you buy at the autozones of the world geneerall just measure the low side pressure and have you add more till the guage is in the correct place. Many people don't READ the instructions so they don't realize the correct pressure varies GREATLY on ambient air temp and Humidity.

The correct amount is determined by weight, typically 1.5-2 lbs of refrigerant depending on vehicle (will generally states it under the hood somewhere on a label or the compressor itself). The recharge stations weight the tank so you know how much your putting into the system by the before and after weight of the tank.

corvettebob1

bighank

Guages can be had for about $39 at Harbor Freight. Get freon in a 12 can case at Sams or Costco.

The Wrench

My 2000 has the label on the passenger fender - 1.5 lbs of R134.
Having just reworked my other car's system, I can testify that monitoring the high & low pressures to determine the freon capacity can be a confusing proposition for the non-expert like me.
The high side will vary all over the place, depending on the time of day, humidity, temp, when the fan comes on, engine RPM, etc, etc. The low side varies similarly, especially with the newer variable displacement compressors. Guys who do it for a living know better how to interpret all this, and can do a good job of getting close to the required qty of freon in the system. My solution, and always the best approach: was to start from scratch, fix whatever is suspected of being bad, evacuate the system to verify no leaks, then just charge with the exact specified amount.

DG

j84buick

To truly know how much R-134a you need you have to measure the high side pressure. Those cans just have a gauge for the low side which is only part of the story. Add too much and your in trouble.

majorpayne317641

True professionals and those who want to do it right will evacuate, leak test, and add the amount of gas by weight, if you want to get it right by looking at pressures, you better have a thermodynamics book, calculator, basic weather station read out, and pad of paper, that's why the best way in the shop or at home is the first mentioned method.

lucky131969

True, and that's why you consult the service manual. There are tables within, that tell you where you should be at based on temp/R.H. , etc.

SaberD

There IS a way to directly determine the amount of refrigerant. using the pressure readings to determine if the system is sufficiently charged shouldnt be too difficult if you have ever taken a basic physics class. Make sure the car has been sitting for a few hours so the ac system will have the same temperature as the ambient air. This allows you to use the ambient air temperature. It is also important because the temperatures will vary throughout the system. just use PV=nRT 2 times. once for the low pressure side and once for the high pressure side, where
P=ac pressure gauge reading on low side or high side
V=volume of low pressure side or high pressure side
n=mass of r134a / molar mass of r134a
R=universal gas constant
T=ambient temperature

the only problem i see with this is i dont think anybody really knows the volume of each side of the ac system. If the volume is known, all other variables besides mass are known. then the amount of refrigerant can be solved for. just make sure you convert to all the correct units when you plug the numbers into the equation. Also be sure to use the low side pressure reading in the same equation with the low side volume and the high side volume with the high side pressure. Once the mass of refrigerant is calculated on each side, add them together to get the amount of refrigerant in the entire system. If its lower than 1.5 lbs, subtract the amount from 1.5 and that is how much you need to add.

if its low, add refrigerant (you will probably have to make a ballpark guess as to how much to add because most likely the amount you need to add is not the amount that comes in a full can), turn the engine on and turn on the ac to crank the compressor for a couple minutes, turn off the engine, WAIT for the system temperature to equalize back to the ambient temperature (very important), take the pressure readings, and do the calculations again. keep doing this until the mass adds up to the required amount (1.5lbs).

so really all it requires is basic algebra skills and a little bit of factor label method for converting the units. The universal gas constant and molar mass of r134a can be found using google.

dougbfresh

This does not work well in practice since there is a compressor involved and the Ideal Gas law does not take into account humidity.


Superheat tables are what's required, so you can see at what temp/humidity the pressures should be.

SaberD

it will not work while the system is running, but it certainly will when the system is not running and the temperature is the same throughout the system. you just have to sit and wait for it to equalize.

majorpayne317641

That's why I said a thermo book, you don't have to do calculations you just need to do interpolation based on the temperature and pressure values of the given refrigerant.

SaberD

That isnt going to do much good because in order to use the tables, you will need to know the temperature of the refrigerant before the compressor and after the compressor. Unfortunately there is no way to measure it in this system. That is why i suggested using the ideal gas law with the system turned off at constant ambient temperature. Then all required values are known.

majorpayne317641

Well atleast we both know what I was trying to say, nevertheless I think personally the most accurate way is simply removing the gas, applying a vacuum and adding a weighed amount of freon, its easiest for time/money in my experience.

The Wrench

OK. I hope you guys aren't really serious. But I got a good laugh.

So, if you know the exact volume of the system, both high and low sides, and know exactly how much oil is in the system on each side since it occupies volume, and understand the variable volume operation of the compressor, and how the compressor dynamically loads the system, and how the TXV valve adjusts the freon flow on the fly, then get all this done within a few seconds of run time before the condensor heats; well of course the formulas certainly yield the answer (if I remember my Physics post-graduate work from 40 years ago).

Or, as Lucky said, just go to page 1-8 in the service manual, and all the answers are there. Of course, the manual is a bit vague about airflow thru the condenser at ambient temps above 70, and thus the critical cooling effect on the condenser, and does not reflect the usual trash jammed in the condensor of all Corvettes. But, if you have accurate humidity and temp gauges, and can take all the airflow variables into account, and guesstimate it within 10 degrees, you're only off 50 PSI!!!! on the high side. That's about as accurate as "throw in half a can and see what happens".

I'll stand by my original low-tech approach - if the system ain't working right, find the problem and fix it, then evacuate the system and confirm it's fixed, and fill it with $15 worth of R134.

Cheers,
DG

All_Motor_C5LS6

good info

lucky131969

You convinced me....the manual is garbage. Your low-tech approach is much better.