Fixed orifice air conditioner not cooling down

[aquasanj]

Hi Super techs,

Recently replaced a maneurop compressor for a 19 Kw ducted split aircon because the exisiting comp had failed mechanically. Problem is that it does not pull down room temp.

Used Nitrogen while soldering the drier and pressure testing. Vaccummed the system and recharged as per manfrs specs based on piping lengths. (7.1 kgs)

(Had also weighed the charge when recovering which matched manfrs specs)

I have the following readings:Ambient temp 33*C/Room temp 26*C

Refrigerant R22

Low side 68 psi
Sat Suction t. 4*C
Suction line t. 23*C

Liq Line 230 psi (discharge 240 psi)
Sat Liq t. 44*C
Liq Line t. 41*C

Indoor unit air on: 26.5*C
Indoor unit air off: 18*C

Outdoor unit air on; 33*C
Outdoor unit air off: 41.4*C

condensor,evaporater and filters are clean

The suction pressure fluctuates between 60 and 75 psi approx every 30-40 seconds, and the orifice in the indoor unit makes a rattling sound during this period.

please help me figure out what is going on here. i know the super heat and sub cooling are out of order . From my knowledge i should expect 9k superheat and 8.5k subcooling. Pls correct me if i'm wrong guys...
Could the "accutrol" ( orifice rattling be the fault???)

cheers

[troymedhurst]

Hi Super techs,

Recently replaced a maneurop compressor for a 19 Kw ducted split aircon because the exisiting comp had failed mechanically. Problem is that it does not pull down room temp.

Used Nitrogen while soldering the drier and pressure testing. Vaccummed the system and recharged as per manfrs specs based on piping lengths. (7.1 kgs)

(Had also weighed the charge when recovering which matched manfrs specs)

I have the following readings:Ambient temp 33*C/Room temp 26*C

Refrigerant R22

Low side 68 psi
Sat Suction t. 4*C
Suction line t. 23*C

Liq Line 230 psi (discharge 240 psi)
Sat Liq t. 44*C
Liq Line t. 41*C

Indoor unit air on: 26.5*C
Indoor unit air off: 18*C

Outdoor unit air on; 33*C
Outdoor unit air off: 41.4*C

condensor,evaporater and filters are clean

The suction pressure fluctuates between 60 and 75 psi approx every 30-40 seconds, and the orifice in the indoor unit makes a rattling sound during this period.

please help me figure out what is going on here. i know the super heat and sub cooling are out of order . From my knowledge i should expect 9k superheat and 8.5k subcooling. Pls correct me if i'm wrong guys...
Could the "accutrol" ( orifice rattling be the fault???)

cheers

Hi aquasanj,

just a couple of questions;

Did you re-use refrigerant?

Is there a small in-line filter before the fixed orifice? Could there be a foriegn object there? I had a similar expierience.

What type of control fan control do you have?

Looking at the temp/pressures you have, it is looking short of gas.

Could the noise be just a shortage of gas going through the orifice?

[mad fridgie]

Sounds like a Temperzone to me.
Add a fraction more refrigerant.
You are getting flash gas through the orifice.

[aquasanj]

Hi buddy,

I charged virgin gas, as for the filter, i can,t tell maybe it is inside the line just before the orifice and the orifice is soldered so i may have to disconnect to check.
The indoor fan is controlled by a wall controller and has 3 speeds. the outdoor fans (2) are fixed speed.
I managed to note down the info i gave when it was sitting at those pressures for a short while during its fluctuating cycles.
It may be short of gas but the liquid line is quite warm (41*C), i did think it may be short of gas but was reluctant to add more than the mnfrs specs....did not want to over heat the liquid line
cheers

[aquasanj]

Hi mate,

Its an APAC unit, you probably heard of these.

I could add more gas but what would happen if my liquid line heats up too much......why would the suction pressure hunt as it does between 60 and 75 psi...not much change in the head pressure though....

cheers

[Gary]

Hi buddy,

I charged virgin gas, as for the filter, i can,t tell maybe it is inside the line just before the orifice and the orifice is soldered so i may have to disconnect to check.
The indoor fan is controlled by a wall controller and has 3 speeds. the outdoor fans (2) are fixed speed.
I managed to note down the info i gave when it was sitting at those pressures for a short while during its fluctuating cycles.
It may be short of gas but the liquid line is quite warm (41*C), i did think it may be short of gas but was reluctant to add more than the mnfrs specs....did not want to over heat the liquid line
cheers

Adding more refrigerant will cool, not heat, the liquid line.

Add refrigerant until the superheat is right.

[mad fridgie]

Hi mate,

Its an APAC unit, you probably heard of these.

I could add more gas but what would happen if my liquid line heats up too much......why would the suction pressure hunt as it does between 60 and 75 psi...not much change in the head pressure though....

cheers

Simply you are loosing your liquid seal at the orifice,
some times liquid, then sometimes liquid and vapour.
Add a little more refrigerant.

[desA]

Simply you are loosing your liquid seal at the orifice,
some times liquid, then sometimes liquid and vapour.
Add a little more refrigerant.

With an effective SC ~ 0K for an air-cooled condenser, would you expect to be able to achieve a full liquid seal at condenser outlet?

I wonder if perhaps the OP could have positioned the new filter-drier slightly differently to the previous one? Is it set in the correct flow direction?

[mad fridgie]

With an effective SC ~ 0K for an air-cooled condenser, would you expect to be able to achieve a full liquid seal at condenser outlet?

I wonder if perhaps the OP could have positioned the new filter-drier slightly differently to the previous one? Is it set in the correct flow direction?

He will not have consistant sub-cooling, (if any at all)
Remember in the service world we do not use highly calibrated measuring instruments. And if they were, after a while being thrown around a service van, they will not be so much calibrated as estimated

[desA]

^

I'll get back in my hole, now...

[mad fridgie]

^

I'll get back in my hole, now...

And i bet she better looking than mine??

[desA]

^ Hahaha... where the 'blush' emoticon?

[troymedhurst]

Hi mate,

Its an APAC unit, you probably heard of these.

I could add more gas but what would happen if my liquid line heats up too much......why would the suction pressure hunt as it does between 60 and 75 psi...not much change in the head pressure though....

cheers

I think the reason you are seeing the system hunt, is because everything on your system has a fixed constant - outdoor fan speed control, compressor and an orifice. If you had a tev and fan speed control, I think you would see the system run a lot more smoothly, but still short of gas.
Also gary is right, If you imagine your hot gas running through your condenser and in to your liquid line, if the liquid line is not full it goes through the condenser too quick and does not sub cool enough.
That is why you are only seeing 3k sub-cooling. If you add more refrigerant and you have a full liquid line, the refrigerant is backed up in the condenser a little longer, enough to be sub-cooled to a reasonable level i.e 10k. I have found that if my condensing temperature is 45*c ,I would normally have a liquid line temp of around 35*c (not always spot on, but around that)
Hope this helps.
Troy

[aquasanj]

Thanks fellas,

Did as per your advice and charged up 330 gms to correct the situation. Apparently whatever i reclaimed was obviously not the correct charge.

Re measured the piping length and topped up to superheat and all seems to be well now.

The super heat and sub cooling are obviously varying as the load changes

Many thanks guys for all your advice,

much appreciated

sanjay