Charging a refrigerant as a gas

[hammy]

Hey folks, sorry about such a simplistic question but I know that some refrigerants are to be charged as a liquid....but this can be difficult to do. If we charge a system on the high side with liquid as far as we can and run it are we okay to then attach a guage to the suction side and crack open the valves on the fridge manifold so the refrigerant liquid boils enters the suction side as a gas.

I wasnt sure if we had to charge it as a liquid so the refrigerant didnt separate inside the charging cylinder into its constituant compenents thus giving us incorrect pressures etc inside our fridge our whether we had to charge ity as a liquid full stop!!

If the refrigerant enters the fridge system like this is it okay. Im anxious not to charge liquid into the suction line but also maintain the correct blend of the refrigerant.

Again sorry if this is a dumb question or makes no sense (it does in my head lol)

[The Viking]

OK,
You have to draw the refrigerant as a liquid from the cylinder.
But you are perfectly all-right to let it boil off to a vapour before it enters the system, there are even special gizmos on sale to do this.

[hammy]

OK,
You have to draw the refrigerant as a liquid from the cylinder.
But you are perfectly all-right to let it boil off to a vapour before it enters the system, there are even special gizmos on sale to do this.

brilliant, thanks for confirming this :)

[Brian_UK]

If you get frost forming on your guages then you have got it spot on :D

[lowcool]

or pass it through a capillary

[hammy]

thanks for the further input guys. As im sure you are aware i dont work with refrigeration that often but am starting to so have really started buffing up on it :)

Can all refrigerants be charged in this manner ie boil it off in the gauges

I have a couple more questions if you would be so kind. I was with a guy the other day who's been in the game many many years and some of his techniques had me a little confused.

When we were about to charge a system i told him I was going to purge the air out of my gauges so we didnt get any air in the system. He said you dont need to bother with that. I didnt really want to argue with him because he's been in the game for 30 years and worked for some of the biggest fridge companies but surely we should avoid putting any air into the system shouldnt we. I then went on to witness him putting a lot of air in the system. When i questioned him again i was told it was alright.

I guess this is why i posted on here so i can get the correct answers and not learn bad practices


I went to another system that had just been charged by someone else and put my gauges on to the compressor. I bled the air off at my manifold (so when i had finished i could boil the refrigerant off in the lines and make sure it went back inot the system and not to atmosphere) but from the hp it started to frost a little bit and get cold as it came out. We shouldnt get this should we (this was as the compressor was running) ? If its a superheated gas then we should have no cooling properties left in the refrigerant until its been subcooled. Could this point to an overcharge or the superheat being incorrect. There was a bit of sweating on the suction line but i was told that was normal (everything i read says that points to incorrect superheat or possibly an overcharge)

I dont really like asking at work cause when i asked about superheat I was informed that you dont need to bother with that.

Im really trying to learn to do this the right way and appreciate the assistance of you guys that can point me in the right direction

[pendlesteve]

Hi Hammy,
Sadly some who have been in the industry for a long time were not very good engineers or have not kept up with the times.
Air contains moisture which of course is a no no in a system. Air also increases the discharge temperature & pressure so increases the power drawn, increases the load on the motor etc.

Not too clear about the second part of your post, could you explain further.

"Don't need to bother about superheat" utter crap! Superheat needs to be set correctly to ensure efficient use of an evaporator and to make sure the risk of liquid returning to the compressor is minimised.

[hammy]

Not too clear about the second part of your post, could you explain further



Cheers for the reply :)

Hopefully this will make it a little clearer
Basically when I purged air from my gauge lines on the hp side with the compressor running the line became cold and on the top thread it went white as if ice was forming. I didnt think this should happen because at this point there should have been no cooling abilities left in the refrigerant should there?...

I was wondering if this was a sign liquid was being pumped through the compressor because the suction line was also sweating. When you purge air from the HP line on your gauges it shouldnt go cold should it..we are pumping a hot gas that has no cooling properties left (until it has condensed again)

Sorry if these are silly questions :)

[TRASH101]

Hello Hammy

First off having the suction line sweating doesn't indicate anything....except that it is cold enough for the ambient air to reach dewpoint. (it also means that, due to the lack of insulation, it has the potential to add to the superheat)

Secondly its not generally a good idea to vent/purge your gauges whilst attached to the hp side of a running system.(a good way to lose the charge and injure yourself)

As for the cooling effect you observed, you are incorrect that the refrigerant requires sub cooling to cool. The refrigerant cooled the hose because of the pressure drop through your gauges.

[hammy]

Hello Hammy

First off having the suction line sweating doesn't indicate anything....except that it is cold enough for the ambient air to reach dewpoint. (it also means that, due to the lack of insulation, it has the potential to add to the superheat)

Secondly its not generally a good idea to vent/purge your gauges whilst attached to the hp side of a running system.(a good way to lose the charge and injure yourself)

As for the cooling effect you observed, you are incorrect that the refrigerant requires sub cooling to cool. The refrigerant cooled the hose because of the pressure drop through your gauges.

cheers for the reply :)

All the books I have read stated that a sweating or frosting suction line point to poor superheat. Thanks for correcting this. I guess everything isnt black or white :). If there is frosting though this is definately a problem though isnt i ?

So i should always purge the hoses with the system stopped <check> ;)

thanks again for the feedback, its much appreciated

[TRASH101]

I'm not saying the books are wrong;)

what I am saying is if you have R410A you measure 90 psig @ the suction service port and the pipe temp is 5 degrees C then say the air is 25 @ 50% rh then its going to sweat (like a junkie without a giro)

i.e. ice/sweat all depends on design and environment.

As for purging, if practical, turn the machine off and let it equalise first. If not then use a valved hose or "quick coupler" to connect to the high side.(this will help to minimise loss)

I worry why you would want to connect to the comp. discharge as knowing the discharge temp. in conjunction with the sub cooling and superheat gives you all the information most people will ever need.

[hammy]

cheers for the reply :)

All the books I have read stated that a sweating or frosting suction line point to poor superheat. Thanks for correcting this. I guess everything isnt black or white :). If there is frosting though this is definately a problem though isnt i ?

So i should always purge the hoses with the system stopped <check> ;)

thanks again for the feedback, its much appreciated


I'm not saying the books are wrong;)

what I am saying is if you have R410A you measure 90 psig @ the suction service port and the pipe temp is 5 degrees C then say the air is 25 @ 50% rh then its going to sweat (like a junkie without a giro)

i.e. ice/sweat all depends on design and environment.

As for purging, if practical, turn the machine off and let it equalise first. If not then use a valved hose or "quick coupler" to connect to the high side.(this will help to minimise loss)

I worry why you would want to connect to the comp. discharge as knowing the discharge temp. in conjunction with the sub cooling and superheat gives you all the information most people will ever need.

pmsl @ sweating like a junkie without a giro

Once again thanks fopr the reply :)

If i had the service valve back seated before i connected the hoses then cracked it to to purge the air from the hoses is this not acceptable. The loss would be minute wouldnt it.

I had thought we can connect our hoses to the high side as part of the working out the subcooling ie measure temp at outlet of condensor, measure pressure of high side and convert this to a temp. Subtract one from the other to give our subcooling. Your reply leads me to believe that this pressure cannot be taken from the compressor outlet...would i need to find somewhere else to take the pressure ie where we have complete liquid (if we had a liquid receiver could i take it from the outlet there) ...is this correct :)

Thanks again for your assistance

[TRASH101]

Sorry Hammy

You are correct.
If you have seated valves then its not such an issue.(Too used to schraeder valves)

When measuring sub cooling/ super heat then the temp should be taken as close as possible to the point you take your pressure. If you take your temp. and pressure at the reciever outlet then you have sub cooled liquid say 2 degrees c (good) say 20 degrees (could be really bad) or -2 degrees (super heat). That only tells you the quality of the refrigerant at that point. Measuring at the expansion device tells you whats going in.

[hammy]

Sorry thats my fault....Ive only ever come across systems with service valves on them so far :)

Should i be taking the subcooling as near to the condensor outlet as possible (service valve allowing) and as near to the evap as possible

cheers :)

[Brian_UK]

Just a small comment going back to your 'freezing' around the hoses.

1. If using Schraeder type connectors then there is a natural restriction through the valve core which will drop the pressure like an expansion valve when gas is flowing through your hose.

2. Frost at the hose connector end can also indicate a leak from the hose seal or the connection is not tight.

[Peter_1]

cheers for the reply :)

... If there is frosting though this is definately a problem though isnt i ?

Perhaps already answered but this can be a normal situation. If you SH is OK, then you don't have to worry.

[Gary]

Here's a thread you might find helpful:

http://www.refrigeration-engineer.com/forums/showthread.php?t=19701

[WINJA]

I been charging liquid into the suction for years , with 404a and 406a its a must , and I think it was copeland that recomended it for their scrolls any way , I dont believe Ive damaged any of the compressors so far , I liquid charge hundreds of units a year and go back to the same units years later and their still ok.
also think of of how many times youve seen an completely iced up evap with liquid flooding back for even a day or 2 with no noticable damage ( except sometimes and you gotta lug a 7.5 hp semi thru a roof space grrr)