heres one for you

[murphyboy]

cold store, -22, r404a.

little comercial / light industrial job.

has a suction seporator on the system....


...heres my problem.


bringing liquid back to the compressor, now i have checked the fan coils are clear, fans running fine, checked expansion valve super heats, both ok (about 6 degrees) liquid line SV wroking correctly, the system is not over charged either.

i really do think ive checked everything i can.

any other suggestions???

[Gary]

If the superheats at the evap outlets are 6K, then it can't have liquid entering the compressor.

[nike123]

any other suggestions???Check suction superheat at compressor suction and measure pipe temperature 25 cm from compressor.
Use precise and calibrated gauges and thermometer. Zero your gauges for altitude. Isolate temperature probe and pipe at measuring point. Use appropriate probe for job. Wait 2 min or more before temperature reading. Post new readings including:

Evap air in temp
Evap air out temp
Saturated suction temp (convert from pressure)
Suction line temp at evap outlet
Suction line temp at compressor inlet

Cond air in
Cond air out
Saturated condensing temp (convert from pressure)
Liquid line temp at condenser outlet

Explain do you have any suction/liquid line heat exchangers and at what points you are measuring pressures and how far from temperature measuring points.

[Goober]

Got a liquid line/Suction line heat exchanger anywhere in the system perchance?

[gregd1401]

May be leaking liquid / suction heat exchanger inside fan coil unit.

[Gary]

Until we see the compressor inlet superheat, we have no evidence that there is a floodback problem.

[murphyboy]

ive taken my pressure from a schrader point i brazed onto the exp equalising line. if i was leaking liquid id expect to be seeing stupid pressures at my suction wouldnt i?

there is a small slop pot which the liquid line does pass through, but as before if liquid at discharge pressure was leaking into my suction id have daft pressures.

[monkey spanners]

What makes you think the system may have liquid returning to the compressor?

[Magoo]

The TX vav is obviously hunting, satuarting suction, equals flood back.

[murphyboy]

ice build up around the compressor windings (bitzer sealed comp), ice cold on suction side of cylinder head, oil sep with frost, oil flushed from compressor sump.


txv is working fine

[nike123]

ice build up around the compressor windings (bitzer sealed comp)

That doesnt mean liquid in compressor. That only mean that suction line temperature and part of compressor is below 0°C. If room is -22°C than evaporation temp is around -27°C to -30°C.
You must have than 27K suction superheat to get rid of ice at suction.




, ice cold on suction side of cylinder head

Same as above!



, oil sep with frost,
oil flushed from compressor sump.

That is probably related!



txv is working fine
Maybe, but 6K superheat at design temperature is litlle to high.

Why is that hard to take measurements we asked, and post it here, than we could make our own conclusions?

[desA]

Good points, Nike.

[mad fridgie]

I am in the manchester area (today), If you need a second pair of eyes, I can assist, cost you a cub of cha and a bacon butty. PM me if you need help

[ekeller]

if ice on seperater may mean you have very cold vapor at-22degress doesnot mean u have liquid

[cool runings]

.

As others have said.

Frost on the suction can garentee one thing only.

The suction is colder than 0 deg C.

Cool runnings.

.

[Magoo]

The enthalpy of vapour will not form ice on suction, unless satuarated, the degree of saturation is the key.
So what is the SST at compressor, and what is the superheat?