Automotive AC Services

[R.P.J]

Guys I would like to find out something after you do ac work on your vehicle I see alot of professional ac shops and also amauter ac technican gas up the system by guess, could someone explain to me when they are gassing up the system how much gas to do they put back in your system. Or do they watch the gauges and guess "ok that's enough"
very rare you would see someone uses an ac scale to put in back the correct amount

[nervewrecker]

Guys I would like to find out something after you do ac work on your vehicle I see alot of professional ac shops and also amauter ac technican gas up the system by guess, could someone explain to me when they are gassing up the system how much gas to do they put back in your system. Or do they watch the gauges and guess "ok that's enough"
very rare you would see someone uses an ac scale to put in back the correct amount

I will like to believe unless you working where the vehicles are manufactured or working on the same model vehicle all the time there is no way of knowing the weight of gas a system will take. Its best to use the gauge pressures to determine if you have enough refrigerant in the system.

[Strugglerzinc]

They have no way of knowing the correct pressure for each vehicle either.

Weight of gas is usually on the sticker under the bonnet. No manufacturer's FSM tells you to refill an ac system by pressure, but as usual trinis know better.

[R.P.J]

Ok so tell me this. Could a technican watch the manifold gauges while he is gassing up and say yes that's good?

A proper charge system gives what reading?

[nervewrecker]

Ok so tell me this. Could a technican watch the manifold gauges while he is gassing up and say yes that's good?

A proper charge system gives what reading?

Yes he can. They do it with domestic and commercial air conditioning systems.
Auto is similar.

Just need to make sure everything is within the parameters it should be and you orn. Not getting into much detail as I'm tired.

Also for older cars that did engine swaps that are not oem the sticker under the bonnet is no longer valid.

Edit, a proper tech should have a refrigerant chart with corresponding temps. The temp on the gauge supposed to not correspond with the measured temps at that point. Discharge side should be lower, suction - higher. Ill leave out the kintty gritty so youtube / internet made techs will go learn instead of google.

[skylinechild]

They have no way of knowing the correct pressure for each vehicle either.

Weight of gas is usually on the sticker under the bonnet. No manufacturer's FSM tells you to refill an ac system by pressure, but as usual trinis know better.

^^^^ THIS ^^^^^ don't forget the trinis who feel dey know more than the manufacturer...pressure testing and checkin for leaks......not a UV tool in sight...I wouldn't even mention the sniffer tool.

Ok so tell me this. Could a technician watch the manifold gauges while he is gassing up and say yes that's good?

A proper charge system gives what reading?

A "proper charge" (if youre using the scale method) depends on ambient temperature as well as other factors.

the correct method would be to weigh out the refrigerant and then put it into the system but most ac techs rely on watching the gauge.

as temp increases pressure levels also increase so lets say if the supplying R134 cylinder was left out in the sun for a good while......and the tech then takes the cylinder to charge up a automotive system....for a car that's already hot...and in the sun....again for a long while.....how much refrigerant will actually be goin into the car.??

[R.P.J]

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Ok guys so what reading would give you a properly charge system.

[bluesclues]

They have no way of knowing the correct pressure for each vehicle either.

Weight of gas is usually on the sticker under the bonnet. No manufacturer's FSM tells you to refill an ac system by pressure, but as usual trinis know better.

^^^^ THIS ^^^^^ don't forget the trinis who feel dey know more than the manufacturer...pressure testing and checkin for leaks......not a UV tool in sight...I wouldn't even mention the sniffer tool.

Ok so tell me this. Could a technician watch the manifold gauges while he is gassing up and say yes that's good?

A proper charge system gives what reading?

A "proper charge" (if youre using the scale method) depends on ambient temperature as well as other factors.

the correct method would be to weigh out the refrigerant and then put it into the system but most ac techs rely on watching the gauge.

as temp increases pressure levels also increase so lets say if the supplying R134 cylinder was left out in the sun for a good while......and the tech then takes the cylinder to charge up a automotive system....for a car that's already hot...and in the sun....again for a long while.....how much refrigerant will actually be goin into the car.??

Maybe it better to charge it while it hot so u will get a fill of expanded gas? Dont want to fill cold and if it heat up the gas expand and bus d tank.. lol im just guessing i know nothing about a/c refilling. But at automotive that is how they pressure my tyres based on temperature. If its hot they put a lil extra so that when it cooldown the tyre will set at proper inlation or something so lol.

Another note about a/c. Is it possible to change the refrigerant type in a car relatively easily?

[skylinechild]

Temp-pressure-chart-33776F1.jpgr134apc1-300x196.jpg

Ok guys so what reading would give you a properly charge system.

if you have the following scenarios :

no gas in system

1. - system already pressure tested & vacuumed - ready to accept refrigerant - check sticker and weigh out refrigerant...and add in. - no sticker on vehicle proceed to #2

2. check outside thermometer for ambient temp....then check the relevant pressure reading for the gauge and SLOWLY add in refrigerant.... - insert long stem thermometer into ac vent to check the temperature drop before and after. stop adding refrigerant wen desired pressure is reached.

system does not have enough Gas - note - if a sticker is present there is NO way of knowing how much refrigerant is currently in the system so you will have to proceed accordingly.

1. connect gauge and check the pressure readings...insert long stem thermometer into AC vent and check temperature. check outside thermometer for ambient temp....start adding refrigerant in the system slowly until the desired pressure is reached.... check temp inside vehicle.... let compressor cycle a few times so to get an avg temp inside the vehicle.

if I was an AC tech....that's how I would do it.

mango tree AC techs feel free to weigh in....

[Strugglerzinc]

Pressure values also vary greatly from one tech to the other, with each saying theirs is correct.

Consider that maybe all of them use the same pressure values for everything from Nissan to Benz. My 15 year old Mazda uses the same values as a 1 year old vehicle? I think not, yet i have seen it done.

High/Low pressure values should only be used to troubleshoot and not as a measure of if there is enough gas in the system.

[nervewrecker]

Leme ask you kids a question:
If I take a can of coke and put it in the sun, I take another and put it in the fridge.
Does the amount of coke in each can change due to the temperature?

Similarly, for a closed system such as an ac system, does the amount of refrigerant change when the temp does?

[Cantmis]

^no

[nervewrecker]

If I was to take two glasses of water, one at 10 deg c and the next at 60 deg c full to the brim, do they have the same amount of liquid?

No, one has less and one has more. If I was to connect a pressure gauge at the bottom of each glass and measure the pressure exerted by the column of liquid I'd know this. And I can use the pressure to determine how much water is in the glass and make sure each has the same amount.
Yay or nay?

So can we use pressure to determine how much of a fluid is in a system?

[skylinechild]

Leme ask you kids a question:
If I take a can of coke and put it in the sun, I take another and put it in the fridge.
Does the amount of coke in each can change due to the temperature?

Similarly, for a closed system such as an ac system, does the amount of refrigerant change when the temp does?

please note in your example your states of matter change went from liquid...to solid (frozen coke) - you compared two bottles of coke.

>>>> if I was to take two plastic bags and fill each with 1 liter of water....freeze one and left the other at normal temp...which would weigh more.??? does the amt of water change <<<<
that is effectively what you askin eah....

no body is saying the amount of refrigerant changes...what we are saying is the Pressure changes.....based on the temp....

HOW much refrigerant is in the system.???
how can we tell .????
if everybody just fullin up till the compressor kick on .... how can you be sure there is the correct amount in the system...???

for any given temperature the pressure reading will change...and it will affect the amt of gas you put in...

say for example... its hot ..like 30 deg outside.... how much gas do you add in..??
do you add in gas till the compressor kick on..??
do you add in gas taking into consideration the ambient temp and compensate by allowing the pressure to rise to the recommended amt.?
do you weigh the gas and add in regardless of temp.???

If I was to take two glasses of water, one at 10 deg c and the next at 60 deg c full to the brim, do they have the same amount of liquid?

No, one has less and one has more. If I was to connect a pressure gauge at the bottom of each glass and measure the pressure exerted by the column of liquid I'd know this. And I can use the pressure to determine how much water is in the glass and make sure each has the same amount.
Yay or nay?

So can we use pressure to determine how much of a fluid is in a system?

AC refrigerant is a GAS --- yes it changes to a liquid and back to a gas
when you adding refrigerant to an AC.... is the refrigerant in a liquid form...or gas form...???

-its pressure rises - due to being compressed by the compressor - temp also rises...so its sent to the condenser to cool off.... temps drops therefore it turns to a liquid...before being sent to the evaporator liquid passes thru the evaporator.....it absorbs heat......the refrigerant is then cycled back to the compressor to begin again.

its this property we exploit to make the air conditioner work...temp changes along with liquids and gasses...and of course..pressure....

nerve... yuh on sheit eah stop tryin to chain up the ppl.....

in both your examples.... you use a liquid.... Ac refrigerant is a GAS....

as quoted by you there are 4 states of matter....solids.... liquids gases....and cat
(a cat takes the shape of any container -usually a basket- its put into but that's a convo for another time )

solids liquids and gases interact different with pressure an temperature. (cat is irreverent here)

copy and pasta here for tuners

Overview
Temperature and pressure are directly proportional
to each other. This means that as the temperature
decreases, the pressure also decreases, and as the
temperature increases, the pressure increases.

One way to think of this is if you increase the speed of the
molecules –by increasing their temperature- the
force of the molecules hitting their container
increases and this increases the pressure. This
relationship is called Gay-Lussac’s Law and makes up part of the ideal gas law.

Theory
When the speed of a gas’s molecules increases, the gas molecules hit their container more often. The
more frequently the gas impacts the container walls, the higher the pressure. So, as temperature increases,
the pressure also increases. If the gas cools, the impacts are less frequent and the pressure decreases.
This relationship can be described using mathematics as well. Mathematically, Gay-Lussac’s Law states
that
P/T = k
where k is any constant.

This relationship explains why race car tires are not filled with as much air as normal tires. At the high
speeds of race cars, the air inside the tires heats up, causing the pressure to increase. Tires with too high a
pressure have less contact with the road and are more easily damaged. So, the cold tire pressure for a
race car is lower than a normal car. As air sinks, it encounters higher pressures and the temperature increases.
This characteristic of gases leads to the definition of potential temperature. The potential temperature
is the temperature a parcel of air would have if it was moved to 100,000 Pa, although this definition
does not require volume to be held constant.

link >>> http://littleshop.physics.colostate.edu ... elated.pdf

for the tuners who want to read about the GAS laws....
https://en.wikipedia.org/wiki/Gas_laws

Boyle's Law --- at constant temperature, the product of the pressure and volume of a given mass of an ideal gas in a closed system is always constant.

in simple terms. .once temperature remains the same....VOLUME AND PRESSURE DOES NOT CHANGE.....

Gay-Lussac's Law --- It states that, for a given mass and constant volume of an ideal gas, the pressure exerted on the sides of its container is directly proportional to its absolute temperature.

in simple terms ... once the gas does not change its mass and volume - ie 0.5kg of refrigerant remains 0.5 kg - once the temp rises...so does the pressure.....

[nervewrecker]

Aint even going to read all that. My example with the coke, I said fridge. It will not be frozen, no change of state of matter.

All im trying to show is that you can use the gauge pressure and temperature in order to figure out if the system is properly charged. You reinforced my point.

Most techs with experience dont usually have to pull out any equip to find a leak. Half the time I already know where a leak is before even seeing the system. And there are other methods of finding a leak without the use of all that high tech equip.

[bluesclues]

Leme ask you kids a question:
If I take a can of coke and put it in the sun, I take another and put it in the fridge.
Does the amount of coke in each can change due to the temperature?

Similarly, for a closed system such as an ac system, does the amount of refrigerant change when the temp does?

Bruh from a physics standpoint. Heat causes 'gas' to expand. So the amount doesnt change. Is not really that u need to check. Is the volume'. Not weight.

[nervewrecker]

Which brings us back to square one, how do we know what volume is needed?

[viedcht]

You could correlate the weight via volume with the cylinder...?

[bluesclues]

You could correlate the weight via volume with the cylinder...?

I would expect that to be a standard practice the volume of the cyclinder is written somewhere on it or in the model name.

[nervewrecker]

You could correlate the weight via volume with the cylinder...?

I would expect that to be a standard practice the volume of the cyclinder is written somewhere on it or in the model name.

Why do we need to know the volume? It's always the same no matter the amount of gas in it. The container don't get bigger or smaller.

[nervewrecker]

When you buying propane, you does buy by volume?

I have two right now to sell of that's the case.

[Strugglerzinc]

You could correlate the weight via volume with the cylinder...?

I would expect that to be a standard practice the volume of the cyclinder is written somewhere on it or in the model name.

Why do we need to know the volume? It's always the same no matter the amount of gas in it. The container don't get bigger or smaller.

And here we have my point that trinis always know better.

Doh study the system designed to work with a specific amount of gas, just fill gas till the pressure "look" correct.

[nervewrecker]

Not supposed to use pressure alone either. If place is cold and there isnt much heat to dissipate the pressure will read low so you keep adding.
As soon as things heat up the pressure will go up and guess what.... your system overcharged.

The original question was if you can use pressure to find out if a system is properly charged. I replied yes and I stand by my answer. If I'm not mistaken I said pressure and temp, not so?
The original question also asked if you can use weight. The answer is also yes but you don't have to.
If someone comes in and want to know if they have enough refrigerant in their system are you going to take it out and weigh it? Leme hear you smartasses now...

[bluesclues]

You could correlate the weight via volume with the cylinder...?

I would expect that to be a standard practice the volume of the cyclinder is written somewhere on it or in the model name.

Why do we need to know the volume? It's always the same no matter the amount of gas in it. The container don't get bigger or smaller.

Thats exactly what i said tho What i also said is weight desnt cater of expansion and cntraction of the gas under different conditions. Volume does that. Basically the same volume of gas can occupy both a 40lb(cold) container and an 80lb(hot) container. The container volume has to be specified based on how much pressure the container could handle not how heavy it is. Gas will have a maximum expansion to pressure threshold before the container explode.

In short... if it hot, under-gas a bit. And if it cool, put the regular amount.

Aight allyuh so this calls to me to mention the same trick i does use long time now to fill at gas station. Filling up when it's cool gets u more 'volume'' of gas.. so when it get hot the gas expands and u get better mileage on your tank... lel. I fill up early mornings or late at night. Filling up midday and after could cost the sacrifice of i think about 20% volume depending on how hot the storage containers are at the time of filling up.

[nervewrecker]

You still doing it by guess.
We don't guess! :Mrgreen:

[bluesclues]

Not supposed to use pressure alone either. If place is cold and there isnt much heat to dissipate the pressure will read low so you keep adding.
As soon as things heat up the pressure will go up and guess what.... your system overcharged.

The original question was if you can use pressure to find out if a system is properly charged. I replied yes and I stand by my answer. If I'm not mistaken I said pressure and temp, not so?
The original question also asked if you can use weight. The answer is also yes but you don't have to.
If someone comes in and want to know if they have enough refrigerant in their system are you going to take it out and weigh it? Leme hear you smartasses now...

Can u use pressure? From a physics standpoint yes. But let me tell u what u need to do without still 'guessing'. U need to know the temperature of the gas at the time of filling up, the relative rate of expansion per degree celcius for the particular type of gas. And factor those in to get the volume u need to fill. Because pressure during hot day and during cold day will result in an offset in the volume.

Using pressure alone? It go wukk because im sure its negligible almost like litres and quarts. But it wont be precise. But say a man using hot hrs figures during cold hrs... yeah he run the risk of overgassing and vice versa. But as long as the container designed to hold the pressure it wont explode. Container should also have a ppi rating 'pressure per square inch'.

So u could calculate it kinda easy. Rate of expansion per degree celcius will tell u exactly how much gas u need at the specific time u gassing. In volume.

[nervewrecker]

Still no.
I ain't hearing the terms of what I looking for.

[bluesclues]

Still no.
I ain't hearing the terms of what I looking for.

I am not an ac man so i dont know u all lingo. Lol

[bluesclues]

I think all your questions would be answered with this link

http://m.inspectapedia.com/site/inspect ... s.php#2752

Basically it pointed out that using pressure as measurement, 'assumes' a temperature between room temperature and body temperature for refrigerants. So i suppose this is the official method and would work just fine as long as ur not gassing outside that temperature range. But basically the same thing i said.. they wrk with psi, rate of expansion and temperature to fill and measure the volume. But doesnt seem to be a necessity since basically, theyve done all those calculations for u already and all is included as the standard regarding the design of the container. So according to what i read there.. yes nerve u are right, just use pressure. With the bluesclues note that that works as long as ur not dealing with temperatures outside the normal working range. If for whatever reason while driving your refrigerant cylinder gets hotter than average then you would most likely suffer overcharging symptoms as each additional degree will increase the pressure in the container beyond the range it was measured and designed to handle for the ac to work most efficiently.


This give me an idea to ceramic coat the cylinder as we here in hot trini. Dont know where in the car the cylinder is stored or if it could even get hot, but if it vulnerable to heat, a ceramic coating might do wonders and keep the ac running cool for longer. Wish i could do such experiments... sigh.

[nervewrecker]

That site only explain the basics. Just enough for google techs.

You guys dont quit your day jobs.