Defrost problem (CLIMAVENETA AWR-HT/CA-E 0302)

[nerijust]

Hello for all,

We have CLIMAVENETA AWR-HT/CA-E 0302 and problem with defrost.

In cold days, when temperature is approx. or below 0, the coils become icy and units stops by Low Pressure alarm. I noticed that defrost starts and ends in approx. 10 - 15 s. I looked at the process and found that then coils is very icy, defrost starting (compressor not restarting) and pressure on LP side very quickly falls below 1 bar and defrost is terminating due to low pressure I suppose and some ice remains on coils.
Units are with standards parameters and factory refrigerant charge.
Maybe somebody had similar unit and solved this problem. Also maybe somebody know right refrigerant charge? We got unit with 19,5 kg charge. In this document - http://www.climacon.com/storage/_files/AW_HT_0122_0302_EN_(389).pdf I found that refrigerant charge is 40 kg.

Thanks all for support.

Nerijus

[frank]

First thing to do is recover the refrigerant and weigh the total charge and compare it against the data sheet you have posted.
It may be as simple as a SOG

[nerijust]

I did that. Unit have 19,5 kg. It is amount that is recorded on the sticker from factory. Is it mean I need do additional charge?

[frank]

If the data sheet says 40kg and you have 19.5 then it's SOG

[nerijust]

Oh, sorry Frank and all. I did some mistake with calculation. Unit have 2 separate circuits. Each of them have 19.5 kg. So 2x19.5 = 39 kg. and I don't have problems with refrigerant charge but have problem with defrost.

[install monkey]

are all the sensors reading correctly, mainly coil sensor

[frank]

Can you confirm that all of the other operating parameters are OK?
Flow rates of water through the HE
Operating pressures etc
How often is it defrosting?

[nerijust]

For install monkey:
There is no coil sensor. Just outside air temp., water inlet and water outlet sensors, pressure transducer, high and low pressure pressostats.

For frank:
All operating parameters are from factory, for change them need unique code.
Defrost starts then low pressure falls below 1,7 bar. Due to bad defrosting some ice remains on coils and second defrost starting earlier as it will be starts after good defrosting.
Flow rate I didn't measured but deltaT on HE is 5 C.

[nerijust]

Can somebody explain purpose and principle of operation of low pressure bypass valve. Here is bypass valve bypassing TXV near water heat exchanger. Valve is controlled by pressostat with is conected to low pressure line.
Thanks.

[NewmanRef]

Can you post some pictures of the valve arrangement? Sounds like you have either hot gas bypass for reverse cycle or a hot gas line to keep evaporator pressure up at low ambient. Some pictures might help.

[nerijust]

Here is refrigerant circuit diagram.11243

[NewmanRef]

Was this bypass installed from factory? Or been added since installation? It looks to me as though the valve opens to bypass liquid round the TEV when in reverse cycle. This in turn would allow the liquid to bypass the receiver and economiser and instead direct it straight to a subcooling coil at the evaporator before reaching TEV. Perhaps installed to prevent sat gas at TEV? How is the pressure switch set up that controls the solenoid? If this isn't set up correctly may be starving valve of liquid which could be causing premature frost build up on evaporator.

[nerijust]

It's factory installation. Just I don't know why it isn't present on circuit diagram, but it is on electrical diagram. The control is simple - it will opens when pressure on low side falls below 3 bars. From diagram you can see that it working only when unit is on chiller mode.

[NewmanRef]

Can you post electrical wiring diagram? It looks as though the pressure switch is connected to liquid line on circuit diagram? So the solenoid valve flow direction is towards the ev/cd and not towards bce?

[nerijust]

Some photos
Electrical wiring diagram:
11274
And some actual views:
11275
11276

[nerijust]

The problem is, that during defrost we have low pressure drop and low pressure bypass is to short to pass it.
Later I'll post some charts from measurements. Waiting for its from my colleague.

[nerijust]

Chart from measurements.

11307