Blocked TEV, Oil?

[GrimsbyGuy]

Just seeing if anybody here can give me any advice on this issue.

I have a problem with a coldroom. It's quite small, only 3m x 3m. It's a pump down system and the condenser is located about 25 metres above the evaporator. I have worked on quite a few coldrooms but none which have an oil separator on the condenser and also the compressor is a semi hermetic Frascold compressor, I'm used to working on fully hermetic.

Basically I was called out a few days ago and found the system tripped on LP. Found that no gas was getting through the TEV. Checked the orofus and it looked clear so presumed the TEV was at fault. Replaced TEV and orofus, system worked fine for 2 days then off again. The restriction once again is at the TEV. On inspection there is oil inside the TEV so I'm guessing this is what Is causing the valve to block up? The ambient temperature for the last week has been about -5 so not sure if this is a factor. The Tev is external equalising. Also the compressor oil sight glass is full. I'm back at the job tomorrow so any advice or pointers on what to check will be a massive help.
Thank you

[seanf]

Is it oil in the compressor sump or liquid?
Is the system short cycling?
What room temperature is it trying to get too?
Is the expansion valve in the room?
Is the condensing unit outside? If so, does the seperator have a heater and a check valve after it?
When you changed the TEV, was it just one out one in, or did you do anything like blow nitrogen down the pipework?

[GrimsbyGuy]

Hi Sean. From what I remember it was oil in the compressor sump but I will re check this tomorrow. The system will of been short cycling as the ambient temp is 9 degrees and the set point is +4 degrees.
The expansion valve is on the side of the evaporator.
Yes the condensing unit is outside on the roof.
Not sure about the heater or check valve, I'll have to check this tomorrow.
I didn't blow nitrogen down it as I just presumed it was a collapsed valve. I will be doing this tomorrow when I call back.
Thanks

[GrimsbyGuy]

Like I said I've never worked on any condensers with oil seperators before. I'll have a good look at this tomorrow. I noticed a solenoid on the oil line and an oil sight glass.

[seanf]

Is there oil traps on the suction line?
A solenoid and glass on the oil return is common for semi-hermetics, should have flow when comp is running, solenoid closed when comp stops.
If the seperator has a heater, it should be on when the comp stops. Sometimes there wired to be always on. Sometimes they might have a thermostat.

[seanf]

With the new TEV in, what superheat were you getting?
Is the condenser fan controlled in any way? like speed control or on a pressure switch or a thermostat.

[GrimsbyGuy]

I can't recall seeing any traps, where would they be located? There definitely wasn't any inside and I can't remember seeing any near the condenser but I'll look for these. Ah so the heater is similar to a crankcase heater on scroll compressors etc? The system is about 7 year old and if there are no traps would this of been a recurring issue over the years? I'll check that the oil solenoid is operating correctly and also look for the heater to test it. If these are in order could the oil be a slow build up over time or could it have too much in? Got zero history about any previous work carried out on this system, I know the oil sight glass was completely full but only really checked when it was running. Thanks for explaining the oil separation process ��

[GrimsbyGuy]

Also what is the best method to remove the remaining oil from the expansion valve?
Thanks

[mbc]

Hi
We have 10 W heater for use in the power body
It goes top of expansion valve (top of diaphragm)
And it works when systems are running.
Check the bulbs of expansion is it mounted correctly?
Danfoss says temperature of power body should be warmer than bulb's.

[al]

I would guess it is moisture, recover gas and pull a vacuum, replace drier. It's normal to have oil circulating in system, stripping TEV allows moisture to thaw and replacing TEV will also remove the sympthoms but not cure the cause.

[seanf]

I can't recall seeing any traps, where would they be located? There definitely wasn't any inside and I can't remember seeing any near the condenser but I'll look for these. Ah so the heater is similar to a crankcase heater on scroll compressors etc? The system is about 7 year old and if there are no traps would this of been a recurring issue over the years? I'll check that the oil solenoid is operating correctly and also look for the heater to test it. If these are in order could the oil be a slow build up over time or could it have too much in? Got zero history about any previous work carried out on this system, I know the oil sight glass was completely full but only really checked when it was running. Thanks for explaining the oil separation process ��

If the condenser really is 25 metres above the evap. Its sometimes recommended to put oil traps every 3 metres, so youd see them on the vertical part of the suction line.

Yer the seperator heater is to try and stop liquid condensing in the oil like a crankcase heater. The check valve is to try and stop liquid refrigerant going back/migrating to the seperator/compressor when the system is off.

The fault could be caused by a few things. Like mbc is saying, it could be an issue with the TEV having being installed poorly originally. It could be like al is saying, it could be moisture in the system. Theres also things like oil getting stuck in the evap can sometimes stop the refrigerant flow.


Also what is the best method to remove the remaining oil from the expansion valve?
Thanks

If the problem is being caused by oil, its probably more from too much sitting in the evap blocking flow.
If the problem is from moisture or from the TEV diaphragm being colder than the bulb, warming up the TEV might bring the flow back.
The liquid line sight glass may have a moisture indicator on it, but I wouldnt rely fully on what it reads too much. They can pick up dirt, discolour and fall apart.
If you get to the point where your pulling the refrigerant out, when vacuuming the system use a torr gauge for trying to check for moisture.
If the TEV superheat is too high or if the system is low on refrigerant, it can cause the TEV body to end up icing up and give you that situation of the diaphragm being colder than the buld.

[GrimsbyGuy]

Thanks for the replies. Been back today. There are no traps fitted vertically. Pressures seem fine. No blockages on oil separator lines and solenoid is working correctly. There is a heater around the base of the oil separator which is live but not pulling any amps and also one going in to the compressor which I'd also getting power but not pulling any amps, couldn't feel any heat from them. On pumpdown the system was cutting out at 20 psi so I've adjusted that to cut out around 3psi to get as much refrigerant back as possible. There is a fan speed controller fitted but looking inside it's previously been bypassed as a few contacts were scorched.
I noticed there was a lot of foaming in the compressor oil sight glass which I'm guessing is liquid flooding back to the compressor, after observing for a while it did settle down.
I really do hope it isn't moisture causing this, especially after all the time I spent there today, guess I'll find out if it comes back in over the next few days. What colour should the oil be? It's running on R449A, previously R404A. It is a tint of yellow, I hope that's the correct colour and not evidence of moisture.
When running the TEV diaphragm is completely frost free.

[GrimsbyGuy]

Yes the bulb for the TEV is mounted correctly.

[seanf]

I noticed there was a lot of foaming in the compressor oil sight glass which I'm guessing is liquid flooding back to the compressor, after observing for a while it did settle down.


I would monitor the suction superheat at the compressor for a while, see if its high enough and reasonably steady. And Id be trying to sort out the seperator and crackcase heaters along with the fan speed controller. All should help with foaming.

[GrimsbyGuy]

Thanks for the advice. Ordered new heaters and fan speed controller. Will monitor superheat when back to fit the parts.