High superheat but major frosting on compressor

[kfjoe]

I have a system which is showing a low suction pressure ( -32 deg c sat )
And a high super heat of 20 deg c
But the compressor is showing major frosting as if liquid flood back and even Sticky to touch , temp at compressor inlet 8 deg c
The evap coil isn't showing any real signs of frosting and the controlled space at -10 deg c and air On off Td is low
There seems to be a lot of oil carried in the system , system is R422d

I'm just confused as to why so much frosting at this temp ?

Any help or advise welcome
Thanks

[james10]

Sounds like its low in refrigerant in theory you shouldn't have frost where liquid is present Low td also
the same as is high superheat

[RANGER1]

kfjoe,
It has been said numerous times in other post, do you have a liquid/suction line heat exchanger
that could be internally fractured?
Some heat exchangers are obvious, while others are built in fan casing of evaporator.
Measure superheat at evaporator bulb to see if its same as compressor, if not its something downstream of TX bulb.

[kfjoe]

No heat exchanger , superheat at bulb 20 and at compressor 18
It's just the amount of frost and how rapid on compressor that I find strange

[padraic]

replace exspansion valve and check the size orofice.... or someone might have screwed open the valve to the last... maybe try adjusting valve to get proper superheat in coil

[Brian_UK]

Is the compressor surface temperature below the ambient dew point?

[kfjoe]

Yes it's at -8 , so I understand it will frost
It's just the amount of frosting and the sticky to touch as if it's liquid
As there seems to be a lot of oil around the system , I'm wondering if this has some bearing on readings etc

[aramis]

1) Maybe you should measure superheat at hours of low thermal load. The system could be hunting then.

2) Check your oil separator, it could be condensing significant amounts of refrigerant. You'll see foaming when the float opens.

[cold.man]

what is your suction pressure?
what is your discharge pressure?
i would suspect also that if the system is on R422d and it is a low temp aplication it should have liquid injection?
is the liquid injection control faulty hence too much liquid in the suction.

[r.bartlett]

what is your suction pressure?
what is your discharge pressure?
i would suspect also that if the system is on R422d and it is a low temp aplication it should have liquid injection?
is the liquid injection control faulty hence too much liquid in the suction.

You could be onto something here.. starved system = high superheat=high discharge temp = liq injection...

[nando]

compressor to strong for the evaporator

[kfjoe]

Thanks for all the replies guys

The superheat isn't as high as I thought , it's 11 deg c
Liquid injection is fine
I have a poor TD across the coil and a low evaporating temperature but airflow is good
No oil separator on this system
There is a lot of oil in the system though and you see this when taking off the low side gauge line
I'm wondering if the oil is effecting the evaporator and giving it its poor TD ?

[monkey spanners]

What oil is it running on? POE or mineral? POE would be better with R422D.

What was fault you were called to fix?

Has the system ever worked since being converted to R422D?

[cold.man]

as monkey spanners said POE is better with R422d
If the system has been retrofitted from R22 and was on mineral oil change the oil to POE or at least a 80% POE 20% mineral oil mix if the compressor is still the same.
oil return with minerial oil on R422d is poor, does the system have an oil saftey switch?
What set up do you have for the oil you say there is no oil sep, what do you have?

[Mark]

AB (Alkylbenzene) Oil is also Miscible with R422D and mixes with the existing mineral oils pre retrofit.

[kfjoe]

It is Poe
And it is an r22 retrofit
Fault was the old not achieving temperature
Has it ever worked properly ? Maybe not since being converted , but I didn't do the conversion
There is no oil sep at all , close coupled system relying on velocity for return
I think you may have something with the oil , I don't know how many oil changes etc were done
I think I will test for mineral oil , but with r422d supposed to work with mineral oil and with a percentage of Poe added im confused why

[aramis]

-32°C suction + 11° superheat = return gas at -21 not +8 like in your original post.

When you measure low temperatures in high ambient you should insulate your probe and up and low river so that your sensor and tube take the gas temperature.

-21°C gas would explain the ice without liquid refrigerant.

[aramis]

Oh and you should pay attention at defrosts if the oil level goes up in the compressor, your evaporator could be logging too much oil.

[D.D.KORANNE]

Loose fins of evaporator ???????? Not enough heat transfer .

[Gary]

Evap air in temp
Evap air out temp
Low side pressure/saturated suction temp
Suction line temp at TXV bulb

Cond air in temp
Cond air out temp
High side pressure/saturated condensing temp
Liquid line temp at sight glass

[kfjoe]

Sorry for the late reply, not been on lately
Appreciate all the replies and help

Evap air on -10
Evap air off -13
Low side pressure 15 psig
Suction line temp at bulb -10

[Gary]

The air flow is okay and the superheat is high. That's about all we can tell without a full set of readings.