R134 Automotive Low side question

[moparkid440]

Hey quick question that maybe you AC guys can explain. Obviously when you're charging up an automotive AC system, it is accomplished by filling on the low side. The freon in the low side line comes from the evaporator as a low pressure gas back to the cars AC compressor. However, I noticed when I'm charging up the system through the low side with my manifold gauge set (as I'm looking through the clear sight glass), I can see the Freon entering as a liquid. It's even suggested to turn the freon can upside down to make sure the can empties, obviously meaning the freon in the can is in liquid form. But Theoretically, shouldn't that freon be entering the low side as a gas, which is what is in the low side normally as it travels from the evaporator? Never had an issue with an AC charge, but just a question I had.
Thanks in advance

 

[clubairth]

Yes you have it right. Don't invert the can, Your just slugging liquid into the compressor. Probably won't hurt it but it can.
Remember that in the AC system it's rarely a pure gas but has a lot of droplets and mist in it. You can't run the evaporator pressure too low or you start to get freezing.
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[Wrench97]

If you meter it in through the gauge set(crack the valve so it goes in slow) it will vaporize at the valve(pressure drop) and go in as a gas. As always if you are unsure put it in as a gas and buy a extra can if needed.

 

[moparkid440]

Ahhh makes sense. Thanks alot

 

[rlitman]

Doing this on a scale with a large cylinder, I'll vacuum out the system, and then allow the vacuum to **** the liquid directly out of my upside down cylinder. If you do it fast enough (before the system pressure equalizes with the cylinder), you can get perhaps 90% of your charge in this way, before you even start the compressor, and with the compressor not running, there's no possibility of slugging it with liquid.

I'll then leave it for a few minutes for the liquid to evaporate inside, and then start the compressor up and finish charging with gas.

 

[bazar01]

Doing this on a scale with a large cylinder, I'll vacuum out the system, and then allow the vacuum to **** the liquid directly out of my upside down cylinder. If you do it fast enough (before the system pressure equalizes with the cylinder), you can get perhaps 90% of your charge in this way, before you even start the compressor, and with the compressor not running, there's no possibility of slugging it with liquid.

I'll then leave it for a few minutes for the liquid to evaporate inside, and then start the compressor up and finish charging with gas.

 

[Ohmthis]

Moparkid440, one thing to note here is that the system has a specific amount of refrigerant required to run optimally. It’s on a sticker close to the radiator or on the upper part of the hood. It will say how many ounces of refrigerant is needed. So using a scale you can trickle in the required amount as a liquid like Wrench97 is saying.

 

[MoonRise]

Not only is there a specified amount of refrigerant, there is also a specified amount of lubricant too.

And the 'freon' in the can is usually going to flash to vapor as it leaves the higher pressure in the can (or in the gauge set hoses) and goes into the lower pressure zone in the low pressure line.

 

[RumT]

Once had a lead mechanic, who was the worst mechanic at the station, thought he would show us up by servicing up a Learjet R12 system faster by liquid, from vacuum, due to a compressor change.

I have never seen a compressor case fracture like that.

He never could grasp the concept of how it happened.

He also never touched an A/C system again.

 

[SGKent]

make sure you do the calculations correctly for the temperatures and pressures involved. Just adding freon won't make it colder if the freon is already at an optimal charge.

 

[Wrench97]

make sure you do the calculations correctly for the temperatures and pressures involved. Just adding freon won't make it colder if the freon is already at an optimal charge.

Too much can actually make outlet air warmer, raise the head pressure and make the compressor work harder make the engine run hotter and reduce fuel mileage(heaven forbid you mess with the CAFE numbers ).

 

[Milton Shaw]

All of the newer refrigerants have to be charged from an upside down cylinder as they are blends and do not maintain the correct mix if charged by gas. I remember when GE recommended charging R12 with the 7 oz can upright until it turned cold and then inverting it to finish off the charge. That was for systems that just took 7 oz as a full charge. That was so that the R12 was charged slow and at low pressure into the system.

 

[MattT]

And the 'freon' in the can is usually going to flash to vapor as it leaves the higher pressure in the can (or in the gauge set hoses) and goes into the lower pressure zone in the low pressure line.

The pressure in the little cans will drop below low side pressure when the can freezes up. That's why it takes forever to charge vapor with them.

What I used to do, before I switched to 30# jugs, was stick the can in a folgers can full of hot water. Keeping the can warm really speeds up vapor charging.

 

[04chase]

ive been doing a/c for some years now . its always the first thing a person will do is assume that it needs freon and adding a bit is all they need.

in recent years , i have seen more and more trucks with a/c overcharges . i had a truck a few days ago blowing hot and pressures were in the normal operating range (r134 , pressures vary largely) . so i recovered it to see if it was losing charge. pulled almost 5 lbs of froen out of a 2.88 lb system. Thanks for the free gas!

 

[rlitman]

All of the newer refrigerants have to be charged from an upside down cylinder as they are blends and do not maintain the correct mix if charged by gas. I remember when GE recommended charging R12 with the 7 oz can upright until it turned cold and then inverting it to finish off the charge. That was for systems that just took 7 oz as a full charge. That was so that the R12 was charged slow and at low pressure into the system.

The topic at hand is R134a. R134a is NOT a blend.

 

[fitter30]

A compressor turns to junk right after it gets a slug of liquid. Compressors of any type are not made to pump liquid. So when charging only crack the manifold when charging liquid and todays systems if they loose 2 oz they could be short. Old freon 12 systems used to hold pounds now its oz.

 

[LS6 Tommy]

Doing this on a scale with a large cylinder, I'll vacuum out the system, and then allow the vacuum to **** the liquid directly out of my upside down cylinder. If you do it fast enough (before the system pressure equalizes with the cylinder), you can get perhaps 90% of your charge in this way, before you even start the compressor, and with the compressor not running, there's no possibility of slugging it with liquid.

I'll then leave it for a few minutes for the liquid to evaporate inside, and then start the compressor up and finish charging with gas.

SOP...

Tommy