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MJF_07
07-12-2006, 06:11 PM
Hi all

i have repaired a leak on a a/c system and whilst looking in the installation manual i find that the maximum pipe length is 20 meters (the run is 40m)

i recharged the system using the formula in the manual and after a short time the whole of the compressor turned to ice as well as the pipework from the evaporator.

am i on a hiding to nothing?

these units have been installed in march 06. never worked correctly and are in a battery room.

the other unit has no leak and keeps freezing up at the evaporator but not the pipework or at the compressor.

i am at the point of attaching to the van and driving off!!

Regards Matt.

Brian_UK
07-12-2006, 06:46 PM
HI Matt, sounds like you've had as good a day as I have ;)

What units are you working on?

Superheat and or sub-cooling readngs are ?

Andy
07-12-2006, 06:57 PM
Hi all

i have repaired a leak on a a/c system and whilst looking in the installation manual i find that the maximum pipe length is 20 meters (the run is 40m)

i recharged the system using the formula in the manual and after a short time the whole of the compressor turned to ice as well as the pipework from the evaporator.

am i on a hiding to nothing?

these units have been installed in march 06. never worked correctly and are in a battery room.

the other unit has no leak and keeps freezing up at the evaporator but not the pipework or at the compressor.

i am at the point of attaching to the van and driving off!!

Regards Matt.

If you just drive over the unit you could say it was an accident;)

Pull out the charge, recharge to the basic factory charge and add refrigerant until you are getting an minimum of 10k suction superheat. Check the air temps off and on the unit, look for about 12 deg c air off, with a drop of 4k accross the evaporator, (remember air off is related to air on).
Then check the subcooling at the condenser outlet on cooling, probably about 2k.
Because you are getting freeze back, check that your evap fan is working and on high speed.

When adding gas and ignoring the usually predicted weights it is still a good idea to weigh in the charge, that way you have an idea for the next time or you can say to the boss that the book weight was wrong and you only added X amount:)

Kind Regards Andy:)

monkey spanners
07-12-2006, 08:20 PM
When you find the correct charge get a lable printer and lable the unit with it, or if the boss is too tight to pay for one, get a car paint touch up pen from Halfords or some such, makes life easier for the next guy:)

I've worked on daikin stuff that was twice the max pipe run and daikin advised to just add 20g a meter or whatever it was to suit the run. Took a long time for the suction pressure to come up when it started though.

Cheers Jon

MJF_07
08-12-2006, 02:19 PM
Thanks Guys...

Sorry for my delay in posting had a bit of trouble with the old rubberband, working ok now..

Right subcooling for a cappiliary expasion device would this usually be higher than that of a TXV?

The running pressures are 40psi and 200psi but adding refrigerant into the system seems to have no effect on the pressures. even when the maths say woah thats enough. 4.8 kg.

you can touch the discharge pipe from the pot and feel it getting warmer and warmer then getting cooler and cooler then it starts the cycle again same at the exit of the condensor so getting any definitive subcooling value is a nightmare.

BTW the units are "HIGH COOL" are they made by or for York?

I am by no means any kind of expert in this field, i am predominantly M&E but got the chance to do the C&G safe gas handling and the C&G BRA flame brazing course and i love this kind of work because it has all the elements and is a challenge which is what i thrive on.. Now where is my tow rope i will sort them....

Regards Matt.

Andy
08-12-2006, 05:57 PM
Thanks Guys...

Sorry for my delay in posting had a bit of trouble with the old rubberband, working ok now..

Right subcooling for a cappiliary expasion device would this usually be higher than that of a TXV?

The running pressures are 40psi and 200psi but adding refrigerant into the system seems to have no effect on the pressures. even when the maths say woah thats enough. 4.8 kg.

you can touch the discharge pipe from the pot and feel it getting warmer and warmer then getting cooler and cooler then it starts the cycle again same at the exit of the condensor so getting any definitive subcooling value is a nightmare.

BTW the units are "HIGH COOL" are they made by or for York?

I am by no means any kind of expert in this field, i am predominantly M&E but got the chance to do the C&G safe gas handling and the C&G BRA flame brazing course and i love this kind of work because it has all the elements and is a challenge which is what i thrive on.. Now where is my tow rope i will sort them....

Regards Matt.

Hi matt:)
are you able to determine the suction superheat:)
discharge pipe temperature has no direct efect on the condenser outlet subcooling
Discharge temperature will always be 50 to 80 deg c on this type of equipment, dependant on the refrigerant used:)
lower than this would indicate liquid entering the suction of the compressor (over charge)

Charge the unit to just below the point where the discharge gets cooler.

Hycool have a fan cycle control that reduces the condenser fan speed on heating cycle to control the discharge pressure of the compressor.
Hycool units are either R22 or R410a the pressures given here are for R22.
Watch for the fan cycle thing on heating, this may be your problem, or you may have a reduced fan speed on an auto cooling cycle. Put the evap fan on manual and high speed and see how it goes, and check the indoor unit filters.

Kind Regards Andy:)

Peter_1
08-12-2006, 06:36 PM
youve ans your own question matt its only designed to do a max pipe run of 20m and its twice that,meaning it wont do the duty and putting excess strain on the comp ect as for the other unit i would check the pipe run capacity and the gas charge

any1 agree?
I don't anyway, so for me he didn't give the answer at all. Adding length doens't frost the compressor :confused:
Why it won't do the duty and why will it put excess strain on the compressor?
What exactly do you mean with excess strain?

Pooh
08-12-2006, 09:15 PM
Can you confirm what refrigerant it is on and how you charged it liquid or vapour, the coolish discharge line at those pressures sounds a bit suspicous.

Ian

Andy W
08-12-2006, 09:30 PM
I presume that the air filters have been checked and the evap coil has been checked with a torch at the air on as well as the air off point for pieces of cardboard or polystyrene, sounds daft but I have had it before.

MJF_07
09-12-2006, 11:35 AM
HI Guys,

Ian the unit is on 407c..

Checked filters etc no sign of restrictions etc..

Andy, question on superheat...

would i be able to take a temparature reading from the outlet of the evaporator just after the flare fitting connects to the unit...?? As access to the end of the evap coil is
impossible.

i had a look yesterday and i am thinking of remounting the outdoor units within 10 meters from the indoor units this can be achieved without too much hassle, does anybody feel this may be the way to go and start from scratch.

Cofreth
09-12-2006, 12:08 PM
What is the 'on' coil air temperature and 'off' coil air temperature of the fan coil unit?

Andy
09-12-2006, 01:20 PM
HI Guys,

Ian the unit is on 407c..

Checked filters etc no sign of restrictions etc..

Andy, question on superheat...

would i be able to take a temparature reading from the outlet of the evaporator just after the flare fitting connects to the unit...?? As access to the end of the evap coil is
impossible.

i had a look yesterday and i am thinking of remounting the outdoor units within 10 meters from the indoor units this can be achieved without too much hassle, does anybody feel this may be the way to go and start from scratch.

Hi MJF:)
Yes I would take the superheat at the outdoor unit, both the pressure and the temperture taken together:)

You could move the units, but are you sure that is the problem:confused:

Kind Regards Andy:)

Pooh
09-12-2006, 01:20 PM
How did you charge the system? with liquid of vapour from the bottle when you recharged it.

When you initially repaired the leak had all the refrigerant leaked out or did you just top up the charge?

If you topped up there is your problem, R407C is a zeotropic blend and requires the whole remaining charge removing if you have a leak and new refrigerant putting in charged as a liquid from the bottle. If this is not done the refrigerant in the system will not be R407C so you will get the strange readings you are getting. Before you move the unit try decanting what is in, vac out and recharge with fresh and see what happens.

Ian

sinewave
09-12-2006, 03:37 PM
If re-locating the condensor to within 10 metres of he evaporator is possible then I'd do that for starters.

De-cant all existing refrigerant, pressure test with OFN, vacuum and re-gas in LIQUID PHASE only to manufactures standard charge.

You now have a known datum point at which the system 'should' work correctly.

This is not to say there isn't another problem with the system, but at least you know the system is within it's design limits which at it's current 40M pipeing, it isn't! :eek:

MJF_07
09-12-2006, 06:01 PM
Hi .


To answer a couple of questions

I recovered what charge was left 1kg. i repaired the leak the correct way as i have been taught.

i am aware of the nature of these refrigerant blends and know as i have stated earlier in the post in charging in the liquid state only..

All i want to do is elliminate as much of the possible problems as i do not have as much experience as many of you guys.

last time i was at site i removed a few ceiling tiles above the rectifyer stacks 17 in total running at 64-68 amps a piece. This helped and brought the room temp down to 25 celsius was at 29-30. At that point the air off the unit was down at 8 celcius but frozen from the evaporator outlet all the way back and including the compressor.

unit 2 keeps going into filter protection (due to the restriction from the ice) and from what the manual says latches and then resets after 6 hours.

Regards Matt.

Brian_UK
09-12-2006, 06:17 PM
Are there any in-pipe filters or strainer at the evaporator that might be blocked ?

Only ask as a Mitsi that I was working on Friday had waxed up the strainer inside the flare fitting, might be something similar.....

Peter_1
09-12-2006, 06:50 PM
I personally think that the fractionation of R407c is more a myth then a fact.

monkey spanners
10-12-2006, 05:47 PM
Hi Peter
I would have to agree. When i did a lot of cfc conversion trials for a previous employer i got to talk to a lot of technical people from Dupont and Rhone poulenc (spelling?)and they didn't seem to think it was a major problem, even if a system leaked and was topped up three or four times. The worst place for a leak was where the refrigerant is changing state, but not so bad if just liquid or gas. Interestingly the letter after the rerigerant number defines its glide caracteristcs, a number ending in A would have less glide than one ending in B etc.
Another thing im not convinced by is that R134a leaks more than R12 due to its smaller molecules, how small has a hole got to be to only let out R134a and not R12? Execpt for uncompatable o rings etc. Most leaks are like tipping sand or gravel out of a truck, make no odds how small the bits are its all coming out.

Cheers Jon

Pooh
11-12-2006, 01:29 AM
Peter and Monkey spanners
First answer any refrigerant that has a glide must have a deferential seperation problem, if one constituant boils before another that part will leak first. Why do the manufacturers insist we charge as a liquid.
Second answer the molecular size of R134A is approximatelt a tenth of that of R12, why is it suggested that we leak test with Helium when using R134A and why are the manufacturers telling us that 80% of the R134A produced is already in the atmosphere through leaks.

Ian

taz24
12-12-2006, 03:57 PM
Hi all

i have repaired a leak on a a/c system and whilst looking in the installation manual i find that the maximum pipe length is 20 meters (the run is 40m)

.

I,d be tempted to think that the run is to long and the system is responding to too much pressure drop.

taz.