low gas?(freezing evap)

[marc5180]

hi, i agree with frank on this,is the unit running 24/7 or? you said that you turned controller off when iced up and found contactor still energized by outdoor control and not dodgy contactor....could someone be turning this unit off at any time in the day? i would imagine the indoor fan stops for what ever reason! you say it a 2 to 1 system is both indoors boards ok, have you seen them satisfy on temp? super heat seems small aswell is both units get refrigerant through...and not just flooding one...let me know how you get on??

cheers

Hi i turned controller off and found the contactor stuck in, i know it was stuck in because when i tapped it it released but i didnt check if it was energized i should have, then i turned the unit back on and the contactor did energize then. No one has access to the room apart from myself and 1 other guy so im 100% certain that no one is playing with the controlls. both indoor units get down to temp then go off then come back on and go off etc.Tried this many times. bot units must be getting some refrigerant through cos both evaporators are iced up

[Brian_UK]

You need to resolve the problem of the contactor staying in.

If it is sticking then it needs replacing, no ifs, no buts, it needs replacing.

Next time, before you tap the contactor check to see if there is any voltage at all at the contactor coil feed. It may be that there is a low level voltage remaining on the coil which is enough to hold it in.

If so then you need to find the source of that voltage. It could be coming from a dodgy relay on the PCB. I seem to remember you having changed the boards but there is no guarantee that the new boards are fault free.

It could also be that the contactor has been moved ? is it mounted squarely? a slight twist can cause the moving parts to stick.

Go with the simple things first, contactors should not stay in when de-energized.

[Gary]

Hmmm... As I stated earlier the dT can only be raised by increasing the compressor capacity or reducing the airflow. We dismissed the former because this has a fixed capacity compressor... but let's reconsider this. What if the condensing unit were oversized for the evaporators? That would give us increased compressor capacity. Perhaps we are looking at a mismatch here.

What is the BTU rating on the condensing unit?

What is the BTU rating on each of the evaporating units?

[Gary]

Hmmmm... I see the evaps are rated at 5KW each...

10 KW = 34140 BTU

The condensing unit is Hitatchi Rci 5H5QE. If those 5's indicate 5 tons, that would be 60000 BTU, a gross mismatch. That would explain the high dT and coil freezing problems.

Hmmm...

[Gary]

Next time, before you tap the contactor check to see if there is any voltage at all at the contactor coil feed. It may be that there is a low level voltage remaining on the coil which is enough to hold it in.

The fact that it shuts off with the thermostat but not the controller would seem to indicate that this is the case, and a new board may be needed.

I would further suggest that this is why the unit is not defrosting itself on low coil temp, i.e. the board can't shut off the compressor.

Perhaps the boards could be swapped between the two units to see if the problem transfers with the board.

[Gary]

As i was at the condensor later on in the afternoon when all the ice had melted the condensor went to start and i heard i funny noise in the condensor and looked underneath the fan and found the suction accumulator totally froze up.. Im now wondering if the unit is overcharged and there is a problem with the accumulator because if you remeber i recovered 7 kg where as there should have been 11.5kg but no leak was found?? What do you guys think

I think somewhere along the line somebody saw the frosted accumulator, made that same "overcharge" assumption and removed 4.5kg. That's why the system only contained 7kg. Overcharge is not the problem. The low superheat and frozen accumulator are all part of the high dT problem.

[marc5180]

Hmmmm... I see the evaps are rated at 5KW each...

10 KW = 34140 BTU

The condensing unit is Hitatchi Rci 5H5QE. If those 5's indicate 5 tons, that would be 60000 BTU, a gross mismatch. That would explain the high dT and coil freezing problems.

Hmmm...

Hi gary no the indoor units are Rci 5hq5e 5KW . the condensor is a 10kw unit Ras10q

[marc5180]

I went back to the unit again today, and changed the compressor contactor and outdoor board on the faulty unit. Turned the indoors on and monitored them all day and they worked like they should, What i found was.... i set the controller to 19DegC and whereas on the other cassettes in the room the return air for both units was 26degc which is why they arent going off.... on the system that we are having problems with on the master the return air gets down to 23degc but the slave gets down to 18degc and obviously stops calling for cooling even though the master still wants cooling. So what happens is that the units are cycling on and off about once every 6 mins. so i think im going to order some wall sensors for both indoors and put them in the same place so the return air is the same and they arent fighting one another.....With regards to the freezing up though, im hoping that changing the contactor has sorted it but we will have to wait and see..........

[frank]

i tried to switch it off by the controller but it didnt switch off the condensor or compreesor for some reason, i couldnt get the cover off the condensor and tried to tap the cover to get it off which resulted in the condensor and Compressor going off

'Nuf Said.

on the master the return air gets down to 23degc but the slave gets down to 18degc and obviously stops calling for cooling even though the master still wants cooling

Are you saying that the indoor units (twin split) are on seperate controllers?
Do the indoor fans shut off when set point is reached?

[marc5180]

No both units are on 1 controller master and slave but i can interrogate the controller to see what the readings are for the master and the slave.

No the fans dont shut off when setpoint is reached they carry on untill itstarts to cool again.

[Mr Cilltech]

Hello!

i get this kinda faults all the time. check if the ice built up is solid or is it frosty.

if solid, your unit is not cycling OFF, check ur thermostat or the unit is undersized and is working hard to reach the setpoint.

if frosty, u have a refrigeration problem, check ur gas charge or probably ur expansion valve is starving the evap coil.

and check ur drain not block, becoz once the drain pan is full it will slowly ice and keep buiding up the coil.

Run the unit for a while and watch the part of the evap start to freeze up, if only couple of pipes are freezing u have refrigeration problem.

if ice starts to built up thru out the coil, check ur fan speed and airflow across the coil. Is the coil Dirty. Is the fan blades Dirty, these are basic things which makes a lot of difference.

[Gary]

...on the system that we are having problems with on the master the return air gets down to 23degc but the slave gets down to 18degc

If the room air is 23C, how can the return air for the slave cassette be 18C unless part of the supply air is dumping into the return and recirculating?

Or perhaps the sensor is wrong? Are you taking actual air on/air off measurements or relying on control interrogation?

[Gary]

Hi gary no the indoor units are Rci 5hq5e 5KW . the condensor is a 10kw unit Ras10q

Which brings us right back to insufficient airflow.

[marc5180]

Hello!

i get this kinda faults all the time. check if the ice built up is solid or is it frosty.

if solid, your unit is not cycling OFF, check ur thermostat or the unit is undersized and is working hard to reach the setpoint.

if frosty, u have a refrigeration problem, check ur gas charge or probably ur expansion valve is starving the evap coil.

and check ur drain not block, becoz once the drain pan is full it will slowly ice and keep buiding up the coil.

Run the unit for a while and watch the part of the evap start to freeze up, if only couple of pipes are freezing u have refrigeration problem.

if ice starts to built up thru out the coil, check ur fan speed and airflow across the coil. Is the coil Dirty. Is the fan blades Dirty, these are basic things which makes a lot of difference.

Hi, the ice is buitl up about 1inch tick all the way around the coil. When ever im with the unit it does cycle on and off...i have tested this several times. All thermostas are fine and working correctly. The drain isnt blocked at all both drain pans are clear, iv checked out the fan took them apart cleaned them. As of yesterday though it hasnt frozen up since i changed the contactor....so im waiting for a call to say it has.

[tonyhavcr]

when units are leaking or I think they ma be I Remove gas and pump it up to 300 pis you will see it drop if theres a leak

[marc5180]

I went back to the unit today to check on it and its been running fine all week (fingers crossed). Its been 5 days now since i changed the contactor and all seems to be well. The only thing that i will have to change is both return air sensors ....for wall sensors...because they are 4Degc apart from each other, so they are fighting each other all the time...

[stevo]

Why not replace the contactor (or swap it with the other identical unit if you haven't got one ! ) i have had this on a wall mount where relay/contactor checks out OK, but seemed to have sticky contacts ! and iced up again after a few days ! worth a try ! (don't think it is a refrigerant problem IMHO ).... good luck

Cheers...

[Gary]

Congratulations... apparently both units are now defrosting themselves. Here's the downside:

http://www.coolerado.com/CoolTools/P...11x17US_SI.pdf

Locate 2C (air off temp) along the bottom of the psych chart... go straight up to the 100% humidity line... now straight to the right to where it intersects with 20C (room temp). The humidity of that air is now below 30%... plus the unit runs less efficiently with a colder coil. It takes energy to dehumidify... and even more energy to defrost.

You still have the delta-T problem.

[RAVISEKAR]

Hi,2 Every 1 I Am Working For York Chillers,anything You Need I Can Help U Thanks To Every 1

[airconadam]

hey fellas just an update from the last time we had all these problems with the hitachi units since we changed the contactor we have had no more call backs or problems and its now fine thanks alot for all your help

adam

[markacs]

THE DELTA "t" APPEARS TO BE TOO HIGH.I WOULD SAY FIRSTLY CHECK THE FILTERS OR THE INNER CORE OF THE EVAP COIL.
I HAVE HAD THE SAME PROBLEM AT A CHAIN STORE GROUP IN SA.CHECK DESIGN AIR QUANTITY.TAKE AN ANAMOMETER DO AN ACTUAL AIR QUANTITY.

HOW WE SOLVED THIS?CUT THE EVAP COILS OUT.(THESE ARE 15 AND 20 TON UNITS).MADE A LARGE TRAY 2,5m X 2m X150mm DEEP.FITTED HEATER ELEMENTS INTO THE BASE,FILLED UP WITH WATER.SEALED COIL REFRIGERANT CIRCUIT.WIRED STAT TO CONTROL HEATERS AND SET AT 55C.DUMPED COIL IN AND WE KEPT TOPPING UP THE WATER.AFTER 2 DAYS WE REMOVED THE COILS.THE WATER HAD TURNED TO SLUDGE AFTER IT COOLED.THE A/C UNITS NEVER EVER ICED UP AGAIN!!!!