help required on checking a lp fault

[moondawn]

hi all,

Today i have been working on a job with an airdale close control unit which has two 2 compressors 2 circuits.
Compressor 2 kept tripping out on LP. The System is r407c.

I attached my gauges to the suction port inside the indoor unit and had a running pressure of around 2 psi. i measured the temp at compressor inlet and worked out the superheat to around 20. I understand this means not enough liquid in the evap, so i then measured the subcooling on the outdoor. attached my gauges to the liquid line and took reading from the liquid line at condensor outlet this was 10.

This was telling me that there was liquid in the condensor, so decided to check along the liquid line for a restriction, liquid line checked out fine, making me think problem with the EEV. they had not so long ago changed this apparantly.

Its the first time i have checked for SC and SH on a system before and was not 100 percent certain my findings would be right.

I decided to reclaim the refrigerant and found there to be around 15kg short of r407c pinpointed the leak which was on a shreader point outside on the discharge distributor pipework.

Could anyone tell me where i am going wrong. for lack of charge i should be getting high superheat and low subcooling shouldnt i. Am i measuring the temps in the wrong place. does it make a difference that the system has EEV. any help please.

cheers lee

[sedgy]

hi moondawn ,
this reminds me of a job that I was on years ago < airdale 2x cond units <
found the liquid line from number 1 went to number 2 so when a system went onto pump down it was trying to get all the gas from both systems into one unit, so I sugest you run +test one system at a time, all the best sedgy,

[moondawn]

hi there sedgy,

I dont think the liquid line is crossed when i reclaimed the refrigerant from the indoor unit, i also checked outside with another pair of gauges and the suspect condensor then had no pressure inside anymore.
so that would mean they are not crossed?

cheers lee

[sedgy]

ok lee, alls good, carry on the good work , sedgy

[Brian_UK]

2psi at evaporator coil outlet = +/- -32°C.

Did you measure a pipe temperature there?

So your pipe temperature at the compressor was -12°C, is that correct?

Also, EEV's need a liquid seal to work properly so if the liquid was flashing inside the line due to the SOG then the EEV may not have been able to work correctly.

[Magoo]

Have you done a system to system comparson. I agree with Brian UK, -32 'C is out side the real bounds of a A/C system . Either system is short of gas or the expansion device is not working.

[paul_h]

What was the actual condensing pressure and the temp of the liquid line after the condenser again?

[NoNickName]

I suspect a stuck solenoid valve, or a clogged pipe. If the system is newly commissioned, I suspect someone forgot a pipe cap in the pipe.

[wilko123]

hi all,

Today i have been working on a job with an airdale close control unit which has two 2 compressors 2 circuits.
Compressor 2 kept tripping out on LP. The System is r407c.

I attached my gauges to the suction port inside the indoor unit and had a running pressure of around 2 psi. i measured the temp at compressor inlet and worked out the superheat to around 20. I understand this means not enough liquid in the evap, so i then measured the subcooling on the outdoor. attached my gauges to the liquid line and took reading from the liquid line at condensor outlet this was 10.

This was telling me that there was liquid in the condensor, so decided to check along the liquid line for a restriction, liquid line checked out fine, making me think problem with the EEV. they had not so long ago changed this apparantly.

Its the first time i have checked for SC and SH on a system before and was not 100 percent certain my findings would be right.

I decided to reclaim the refrigerant and found there to be around 15kg short of r407c pinpointed the leak which was on a shreader point outside on the discharge distributor pipework.

Could anyone tell me where i am going wrong. for lack of charge i should be getting high superheat and low subcooling shouldnt i. Am i measuring the temps in the wrong place. does it make a difference that the system has EEV. any help please.

cheers lee

Hi Lee, i would check to make sure you took the readings correctly ''Its the first time i have checked for SC and SH on a system before and was not 100 percent certain my findings would be right.'' Like Brian said your suction line temperature will be -33 deg C at this pressure so to have a suction superheat of 20 your pipe temperature must of been -13deg C??? Im sure this was not the temperature otherwise you would have major frosting on the compressor. EEV could be to blame, it sounds like a blockage so long as your superheat and subcooling readings are correct.

What was the name plate refrigerant charge?
How long is the dx pipe run?
size of liquid line?
Is this a new install?
What is the discharge pressure and compressor body temperature
What is the full load amps on the name plate?
What are the running amps?
What is the EEV valve positioning on the controller?

There are many ways of checking whether there is a low charge, some systems are trimmed so they dont actually contain what it says on the tin!.... 15 kg short on a close control unit sounds pretty short generally and 2 psi back pressure is a dead cert if there is nothing resticting flow.

Hope this helps?

rgds Wilko

[moondawn]

hi all firstly i see i have made a mistake in measuring superheat, my suction temp at the compressor inlet was 22degrees c. I have then taken 2 psi and subtracted that which is why i have superheat at 20. So my real superheat would be a lot higher at over 50? This still means that evap is starved of liquid more so.

so i have calculated wrongly but on the subcooling side i remember taking the temp of the gauge reading and subtracting the liquid line temp which i think was around 30 degrees c. As i rememeber checking along the liquid line for around this temp across filter drier.

like i say never done this before and still learning so possibilty i am making a mistake. I am fairly certain my test on subcooling was accurate and was getting 10 subcooling meaning enough liquid in the condensor.

This job will be the death of me!!!
Today i returned to site to which i had left vaccing all night, the vac was good did a pressure rise test and got 2 torr.
I charged with 10kg of r407c Liquid into the liquid line at the indoor unit, Set the temp at the remote to 15 degrees to run both circuits and then proceeded to add the final charge however both contactors pulled in for a second and then clicked back out both faulting on compressor 1 trip and compressor 2 trip


Another engineer with me yesterday had knocked the mcbs of for the compressors which i never knew, i noticed this switched them on and reset the system. Still doing the same

I disconnected one of the compressors to see if this was affecting the contactor pulling back out but this made no difference.

what i cant understand is i have not touched circuit 1 yet it is now tripping it was fine yesterday.

circuit 2 which had the leak no has more refrigerant inside it.
i managed to get the full charge in later on but still doing the same.


The system is not newly installed model number for airdale unit is DF90XD-AT

[Brian_UK]

Sounds like the LP switch is sensitive.

Anyhow, check the contactor control circuit to find the cause from the drop out.

[moondawn]

thanks brian

thats what i will look at tommorrow, why would my works i have undertaken on the second circuit have a knock on effect on the other circuit. the system has seperate compressors and condensors?

[Brian_UK]

Sometimes control circuits can be linked so that at certain times all hell breaks loose.

Or, you could have a loose neutral in there somewhere.

[moondawn]

thanks brian i will try checking neutral tommorrow too. all hell breaks loose is a good way to describe it. its worse now than what it was with the leak fixed and fully charged!!

thanks all

lee

[moondawn]

hi there an update on the job.

went back to site today, checked the neutral and hp switch lp switch klixon. (thanks marc) still could not find out whats wrong all checked out okay.

found there was a problem getting a command from the serial card PCO board

the engineer who worked on this equipment last year recalled that on the drop down menu dehum hum heat and cool were showing, however now it was only showing cooling only.

Airdale assisted in putting the unit back to a fully functioning unit via input of settings. still no joy, we then noticed that the eev were not functioning and again went through settings with the unit next to us and through tech support. set up the eevs as this has also been lost. still no joy

finally i noticed condensor said CU on the faulty unit yet the one next to it said C.
Changed this retried the system and there it was all working again.

so its lost its settings and reverted back to factory settings.
There is a circular flat battery on the PCO card i think what has happened is when it was left on vaccum the other engineer has isolated the power to the unit, i think the battery has failed and all settings lost.

i normally leave power on when doing this sort of thing for crankcase heaters and disable a switch or interconnecting this will be an absolute must for me from now on.

Anyone else had problems with the battery?

after fixing the unit the client said that they have had issues previously with it losing its settings.

cheers
lee

[Brian_UK]

Thanks for the update Lee, good to hear that you have resolved the problem; as any good RE member would do, of course. :)

[marc5180]

One for the Memory bank Lee:)