Terry VS Oil Problems.

[HelpCoolIt]

I must emphasise that I am an experienced Domestic Aircon serviceman that has been thrown in the deep end over the last two years. I now belive I can call myself a real fridgie. but I am still on a steep learning curve.

I have just replaced a Terry VS (V4) compressor on an old 400 gallon milk Vat with a reconditioned one. The old one seized and locked solid, gas charge gone, Oil everywhere shaft seal assumed to have failed. After re-commissioning with a new dryer in circuit I monitored the operation and found the oil levels dropping.
Upon further investigation I found the filter in the rebuildable Temprite 923 oil separator (never seen one before) to be torn and replaced it (this was then assumed to be the cause of the original failure), cleaned out the oil separator canister and used new oil.
Monitored operation removing excess oil as required.

Luckily I have a very smart farmer who also watched the system after I left.......Two days later I received a call, the oil level is very low. I returned, disassembled oil seperator to check new filter, rechecked float, rechecked needle and seat then over filled the oil seperator and pressurised it forcing oil back into the compressor confirming the oil seperator is working, monitored, then left.......Next call, Oil levels to high suggested run the vat and the oil rectified itself.

Today called oil low again. Added oil to compressor to prevent seizing, no apparent damage done so far. confirmed warm oil return on separator. Separator appears to be still working.
I did a pump down test, compressor pulled down to negative pressures in a reasonable time and then with the suction service valve front seated it held them.

This is a 30+ year old system. If the oil seperator seams OK and the compressor seams OK what else could be causing the erratic oil levels.

A friend suggested that Terry VS compressors were cast with the sight glass too high and will normally show low oil levels but I have another exact same system with a worn shaft seal that I have overfilled with oil to keep in operation till another reco compressor arrives (tomorrow) that system barely fluctuates

My boss has suggested that if the rings weren't done in the reco then the oil could be atomising as it blast past the pistons into the refrigerant and be carrying past the seperator. But from my test I believe the rings to be OK

With the testing that i have done I don't understand how anything could be causing an oil level problem, this system hasn't had a problem for 30+ years.

Does anyone have any ideas as to were I might look next.

Thanks
Dean

[HelpCoolIt]

sorry about the spelling

[monkey spanners]

Hi Dean,

Is it a DX or ice bank tank? What refrigerant and oil is the system running on?
Does it have more than one txv?

I have seen systems where one txv (system had three) had partially shut down causing the refrigerant not to have enough velocity to bring the oil back out of that part of the evaporator.

Its very rare to have an oil seperator on milk tanks in the uk, i can only think of a couple where they are fitted. Are you sure it is working ok?

If you are getting liquid returning back to the compressor this can lead to increased oil carry over.

Different types of oil can do odd things also, is your new compressor filled with the same type of oil as the original?

Jon

[Magoo]

Hi
The Terry V4S "S " for splash feed oil lubrication. So needs a good oil level in sightglass.
If 30 year old system , perhaps the TXV is the original problem. The V4S were not very tolerant to saturated suctions.
Plus all the oil in system could be creating slugging as well.
magoo

[HelpCoolIt]

Hi Guy's
the Vat has two fixed plate orifices (direct expansion). Its Running on MP39 (401A). MP39 is used as one of the replacements for R12 in Australia.
I've used Zerol (alkylbenzene) oil the original oil would have been mineral or alkylbenzene, and the system has a suction line accumulator on it.

With Fixed plate orifices (critical Charge) I assume the suction accumulator shouldn't be necessary.

Refrigerant velocity...... The system appears to cool very efficiently and has an SST of -15c, should it be closer to -12c ? if the system is undercharged the this could effect the oil return.

I had assumed the oil seperator was there because of the Terry VS's oil requirements. The Temprite 923 oil separators are meant to be one of the best. The older 3 cylinder copeland compressors never had them.

This is the first time I've had an oil separator apart but it has a new filter in it (Original had been damaged when the original compressor failed), the float is in one piece and the needle and seat is clear from debris and opens and closes with out any sign of sticking.

Thanks
Dean

[monkey spanners]

The trouble with those fixed orifice tanks is that they are difficult to charge, with a lot of warm milk in the tank they are undercharged, with little milk in the tank they can flood back which is why the have an accumilator (and no reciever).

Are they running it with enough milk in it? Many times i've seen snapped conrods due to the herdsman turning the tank on too soon, especially if they are new to the farm.

The evaporating temperature seems low to me a for DX, is there any ice in the tank when the tanker empties it (as a side note, any ice can effect the wash system as it takes all the heat from the hot wash if fitted, and milky water is recirculated during wash)

The two Fabdec DX tanks i look after both have icebuilders also on the same units and i charge these to the frost line in the icebuilder. They hold 3.3kg of R22 and 100g either way really effects their opperation.
The other thing these are sensitive to is condensing pressure, the Fabdec ones cycle one of the two condenser fans to control it. when fans cycle the evaporating pressure rises and falls with the condensing pressure.

I have converted one system to txvs and a reciever and removed the accumilator when the accumilator rusted out as it wasn't much more expensive in parts and would work better.

What make tank is it? does it have a evaporator pressure regulator?

I've got a chart somewhere for charging the Fabdec tanks to pressures at a give milk temperature, i'll see if i can find it out, you could convert it to the equivalent pressures for R401A to give you a starting point.

[Emmett]

Dean
interesting problem, I am having a similar problem with oil return and a Temprite seperator, (first one for me as well) as it is I am currently awaiting the local Temprite represenative's arrival, I will keep you posted with what I learn.

[monkey spanners]

This is from the Fabdec manual for their mkII orifice model R22 :-

Half fill tank with water at 10c, charge system to a pressure of approximately 60 - 70psig. If the water temp variies from 10c suction pressures will be as follows -

13c = 4.3 bar
10c = 3.8 bar
4c = 3.4 bar

If at low temperatures frosting back occurs on the suction line past the accumilator, reduce charge.

_______

Don't ask why they change from psi to bar :confused::D

This works out as -

13c = 2c evaporating temp
10c = -1c evaporating temp
4c = -3.5c evaporating temp

These presssure are taken at the evaporator outlet and this Fabdec system has no evaperator pressure regulator.
You would need to convert temperatures to pressures for R401A.
These guide pressures tend to be a bit on the high side and often i end up having to take some refrigerant out again at low milk/water temperatures and volumes.

I am not saying this will give you the correct pressures for your system, just that this is from something that works similarly to what you have.
When you do find the correct charge, it is worth marking it on the unit, one of those paint touch up pens for cars is handy for this.

Jon :)

[Magoo]

Hi HelpCoolit.
I think your problems stems from swopping out refrigerant charge for latest drop-in. The fixed orifice injectors are designed to a bee's willie tolerance. Change the differential across that orifice at design conditions and all hell breaks loose.
In NZ we had Burkett re-injection orifices on dimple plate vats, sounds similar to yours. A dirty/partially blocked condenser really stuffed things up. Dead compressors everywhere.
Look at the critical charge senario on R 12 and duplicate with your current gas charge.

[Emmett]

Just a quick update on my oil return issue. The Temprite represenative was not a lot of help, we did however open up the unit and clean it out, we also replaced the filter inside the canister. This did resolve the issue for about a week and now it is back. The commissioning technician found a lot of debri in the bottom of the unit, I have suggested that he check it again to see if there is more debri.