Is this right?

[marc5180]

I've been working on an Airedale CUHS3 today that needed the 4 way valve changing.

There was no indication of the gas charge on the side of the unit:mad:.

I rang Airedale yesterday and asked them what the standing charge was and what the additional grammes per meter was.
I was told the standing charge was 1.7kg plus 50g per meter after that, since the pipe run was 40 meters then the total charge should have been 3.7kg.

I charged the system up but it kept shutting down on LP. I blocked the condensor coil up to raise the head pressure and found superheat to be 30K and the sightglass flashing..... I continued to add refrigerant at 250g at a time until the sight glass had stopped flashing.

The subcooling was 5K and the superheat was at 7K, suction line sweating and good air off temps, everything looked like the system was working good apart from the fact that i had in total charged 8.5KG how can this be?

I left it 15mins each time that i took SH and SC measurements by the way.

[al]

marc

standing charge is correct, additional charge according to the manual i have is 100g per meter, pm me and i'll send the manual (it's for close control but condensing units are standard?)

al

[laf100]

From my limited experience with Airedale's, I would say your final total charge of 8.5kg sounds about right to me. If pressures/temps & especially S/heat are good, pack up & go home!!

[marc5180]

If pressures/temps & especially S/heat are good, pack up & go home!!
I did:D

Just seems a lot of refrigerant for that size unit, hopefully i'm wrong.

[monkey spanners]

How much refrigerant did you take out to change the 4 way valve?

Does it have a txv or is it a capiliary system?

(haven't a clue how much they hold, never worked on one :o :D)

[VRVIII]

Hi Marc,

Do you know if the pipe sizes were standard for the unit? or could they have been increased?

I've never been impressed Airedale charge calc, I only use it as a starting point.

I agree with laf100, you were safe to pack up & head for home :D

P.S. Was this the airedale unit from previous post, re-tripping on LP?

[marc5180]

How much refrigerant did you take out to change the 4 way valve?

Does it have a txv or is it a capiliary system?

(haven't a clue how much they hold, never worked on one :o :D)Hey MS, hope you are well:)

It has a TXV and i only got out 2kg bearing in mind that this hasn't worked for the 12 months tht it has been fitted.

It is the 3rd stage external condensor for an AHU and doesn't call for it often hence the reason why it hasn't been flagged up earlier.
Hi Marc,

Do you know if the pipe sizes were standard for the unit? or could they have been increased?

I've never been impressed Airedale charge calc, I only use it as a starting point.

I agree with laf100, you were safe to pack up & head for home :D

P.S. Was this the airedale unit from previous post, re-tripping on LP?

Hi VRVIII,

I think the pipe sizes are standard 3/4 and 3/8th, the only reason i'm querying the charge is the fact that i worked on another airedale system the other day where the condensor coil needed replacing and the pipe sizes were 1"1/8th + 1/2" with a pipe run of 30m but the charge was only 6kg.

It is the same type of unit but not the same site.
We have a big contract with a company who have sites all over the country that have AHU's with 2 internal circuits and 1-2 external airedale condensors as stage3/4.
We are having many problems with them that seem to be linked to the lack of airflow...the manuafacturers are aware but in the mean time compressors are constantly tripping.

[thebigcheese]

had a problem similar myself. changed the valve on an airwell split, weighed in the charge that was on the name plate (think somewere around 3kg)

sytem seemed to be undercharged but my scales where nearly new.

rang tech and he tells me aww dont go by the nameplate

so i charged her up and was home for dinner

how can this be right tho altho i no from past experience the kit isnt great

[Gary]

I've been working on an Airedale CUHS3 today that needed the 4 way valve changing.

There was no indication of the gas charge on the side of the unit:mad:.

I rang Airedale yesterday and asked them what the standing charge was and what the additional grammes per meter was.
I was told the standing charge was 1.7kg plus 50g per meter after that, since the pipe run was 40 meters then the total charge should have been 3.7kg.

I charged the system up but it kept shutting down on LP. I blocked the condensor coil up to raise the head pressure and found superheat to be 30K and the sightglass flashing..... I continued to add refrigerant at 250g at a time until the sight glass had stopped flashing.

The subcooling was 5K and the superheat was at 7K, suction line sweating and good air off temps, everything looked like the system was working good apart from the fact that i had in total charged 8.5KG how can this be?

I left it 15mins each time that i took SH and SC measurements by the way.

What were the air on and air off temps?

[marc5180]

I can't quite remember the exact figures, i had them wrote down but the td on the airflow on both evap and condensor was ok so somewhere between 5C and 10C.

Also Delta T's seemed fine 15-20C.

[Gary]

I can't quite remember the exact figures, i had them wrote down but the td on the airflow on both evap and condensor was ok so somewhere between 5C and 10C.

Also Delta T's seemed fine 15-20C.

When fine tuning an A/C, everything starts with the evap leaving air temp. In order to get 50% RH the leaving air temp needs to be about 11K/20F below the temp at the thermostat. Assuming the coil is fully active (normal SH) the fan speed should be adjusted to achieve the desired leaving air temp.

If the fan speed is too high, then the coil uses more refrigerant and therefore more refrigerant needs to be added in order to clear the sight glass. Then you can't tell that it's overcharged until you get a hot day.

It's important to adjust first things first... and airflow is first.

If we assume the entering air is the same as room temp, then dT (air in minus air out) should be about 11K.