Replacement TXV for Grunert holding plate using R12

[botanybay]

Below is background but the question is what is the correct TXV for a Grunert R12 based deep freeze system.
Installed when I bought boat: Eaton 223 FA 1/2 9 degree superheat
"Borrowed" from fridge loop to limp along last year: FF-1/2-C with 26F superheat
Manual from later version suggests: FS-1/2-ZP for R409A for the freezer.
Have located a FF-1/2-ZP which would be the R12 version of the R409A valve

My best guess is the FF-1/2-ZP is probably what was in there to begin with. Any other recommendations?

Backup Details for those so inclined:


Over the last 10 years I have had good success keeping my Grunert refrigerator and freezer box running.

A few years back the fridge holding plate developed a leak between the refrigerant and the eutectic solution. After drying the system and removing the refrigerant loop I got it running well.

Last season the txv control became intermittent, i.e. could not move frost line around or adjust as expected. I swapped out the TXV from the fridge side to make a trip happen and it worked reasonably well getting the plates to about 20F. The fridge is running in spillover with a thermostatic fan.

This spring i decided to get the freezer working correctly (it used to go to 0F easily and would go to -15F if left running). I had known that somewhere along the way a second plate was added in series and that the txv was on the vertical line between the two circuits of the second plate. So I have cut away at the freezer box to access the suction line and moved the bulb onto the horizontal portion of the line.

At this point i see much better positive control with superheat and the second plate freezes first and completely before significant frost shows up on the first plate. The only issue is that with the refrigerator txv i can control the frost line but when it gets to 20F it just stops. The repurposed fridge txv is:

Sporlan: Ff-1/2-C which notes its superheat mid range is 26 degrees.

Suction pressure at the compressor case is 6-7psi (i.e. -4.4F to -6.6F at the txv). Temperature at the TXV bulb is 23F to 26F. So superheat is 23 - (-4.4) = about 27.5F which is near the stated value on the refrigerator TXV. I suspect measuring at the compressor case and with 15 feet of 3/8" line the actual pressure is a bit higher in the plate.

The target according to the manual is 10F to 12F of superheat. I suspect the choice of a fridge txv with a large superheat value allowed the fridge and freezer to run peacefully in parallel.

The freezer TXV which came with the system (when I bought the boat, does not look original):

Eaton 223 FA 1/2 9 degree superheat.

This valve worked well in the system before it started becoming "sticky" resulting in either an inability to get below 20F or significant frosting of the return line without control. Considered moisture intrusion from above event but new dryer, evacuation to 150 microns for 2 days, and site glass moisture monitor is green.

This was when I swapped out the freezer txv with the one from the fridge and good good control but with a lowest temperature of about 20F. Pulls down from room temperature in 90 minutes, cycle time is 25 minutes and very repeatable. Frost line moves as expected with 1/8 turn.

This is consistent with sporlan's documentation of the FF-1/2-C being useful from 50F to -10F.

Reading the 2002 version of the Grunert manual (which appears to be an R409A system) recommends:

FS-1/2-C - for fridge applications
FS-1/2-ZP - for freezer applications

With all that said, I need a new TXV for the freezer side. The question is which one.....

I have found old (unused)

FF-1/2-ZP - This should be R-12 version with maximum operating pressure. The difference of the Z and ZP from Sporlan's documentation:

Type ZP charges have essentially the same characteristics as the Type Z charge with one exception: they produce a pressure limit Maximum Operating Pressure (MOP). ZP charges are not
intended as replacements for Z charges. Each should be selected for its own unique purpose.

I have found FF-1/2-C which I don't know if they all have the 26F midrange for superheat?

So the long winded question is: what TXV should I be looking to use for freezer (targeting 0F) as that is what the plates are setup to use.

I suspect the original valve was the FF-1/2-ZP but the 1985 manual does not say what was used. Only the later 2002 manual.

BTW: I enjoy learning on this system and putting a few dollars into is and having it work is fun. I did get the proper license, use a recovery pump, and reload the system with the refrigerant I pull off.

[Richard Kollmann]

Your questions are best answered by Sporlan valve engineer but first they will need a simple design description of your mobile refrigeration system: Compressor HP, number and size of eutectic plates in each box and solution freeze point temperatures . How is temperature controlled in each box? By thermostat and solenoids? How are the different refrigerant evaporator super heat's between each box controlled? Is this control only as a result of TXVs or is there a low pressure regulator on refrigerator plates.

My experience with eutectic plate flow control TXV most use a full range Flare to Flare internal equalized valves +40 F to -40 F range and standard MOP. Valve max orifice size to match that boxes plate or plates total size and no larger to reduce exposure to liquid flow back on compressor start.

[botanybay]

Originally Posted by Richard Kollmann

Your questions are best answered by Sporlan valve engineer but first they will need a simple design description of your mobile refrigeration system: Compressor HP, number and size of eutectic plates in each box and solution freeze point temperatures . How is temperature controlled in each box? By thermostat and solenoids? How are the different refrigerant evaporator super heat's between each box controlled? Is this control only as a result of TXVs or is there a low pressure regulator on refrigerator plates.

My experience with eutectic plate flow control TXV most use a full range Flare to Flare internal equalized valves +40 F to -40 F range and standard MOP. Valve max orifice size to match that boxes plate or plates total size and no larger to reduce exposure to liquid flow back on compressor start.

Thanks Richard,

I am about to reach out to Sporlan and see what they recommend as a proper replacement. I am hopeful that someone with one of these systems can look at what was originally installed just to get a starting point. While the 2002 manual called out a specific TXV the manual from 1984 did not. And then there is the R12 valves becoming hard to find and having to cross reference.

I did find this discussion of MOP valves which is very useful, especially on how to avoid "charge migration" in the devices.

https://www.achrnews.com/articles/13...-pressure-txvs

By "Standard MOP" are you meaning that normally these systems are setup to use MOP to avoid having the evaporator pressure rise above a specific point or are you saying that these types of systems did not generally use MOP type TXVs.

Thanks again for all of the input over the years. I have kept this system running for 10 years now. Enjoying making it work better over time and when it dies I will be in a much better position to select and maintain the next system.

Sincerely
David

[Richard Kollmann]

Mobile refrigeration especially with eutectic holding plates are rarely in need of a Medium Operation Pressure range valves. The object of a eutectic plate is to store phase change energy from an oversize compressor as fast as possible in each plate. This is why I listed the typical TXV with +40 to -40 range. MOP gas valves are generally used in standard evaporators where a normal evaporator temperature range is preferred. To prevent damage to system operating at too low a pressure Grunert uses a low refrigerant pressure switch to stop compressor before pressure goes into a vacuum. Their design engineer at that time had a reason why he wanted MOP control so if you can stay with his design you will not go wrong.

If both freezer and refrigerator TXV are open at the same time their super heat orifice adjustments must be set so refrigerator valve will not increase flow at a greater flow temperature than freezer valve. I am assuming this is why there are separate recommended super heat adjustment ranges on both valves.

[botanybay]

Thank you again Richard!

I think I am heading in the right direction and intend to talk with Sporlan in the next couple of days.

At your recommendation I made up a simple system diagram to aid in that discussion.

I doubt that the available FF-1/2-ZP is a bad choice and it is available.

On a different diagnosis, is there any simple way to check a TXV when it is out of the system.

With the better (proper) location of the sensing bulb (on the horizontal line coming out of the plate) the system is behaving much better and would be near perfect for a fridge, just need to get it down to -10F rather than +20F which is probably being limited by the fridge TXV.

I noted that the pigtail (closed off capillary on bulb) is horizontal and should be on the high side according to some dandoss literature. I plan to try that before swapping out the TXV. Might try the one which was on the freezer (the eaton 223) and see if it was a TXV charge migration issue

[Cpt Mark]

I went through my manual circa 1994 and there is no part listing for the valve. I am in the process of replacing the entire system as mine finally died. I may be able to get to the TVX valves today and pull part numbers. My unit had 2 compartments, 1 refer, 1 freezer. I'd think the valves would be the same but maybe not. Side note. I leaked all the gas out which is why it stopped working. Won't go into all the why's but the refer guy I had out said it was D.O.A. and just not worth repairing. The TVX valves should be fine as well as the compressor, fan unit etc. If you want spare parts, pay the shipping costs and I'll send you what you want.

[botanybay]

Thanks for looking at the valves! I am very curious if both the fridge and freezer are using the same valves.

Is that an R12 system?

Are you reusing the holding plates or would they be available? As noted one of my plates failed some years ago and I am running just the freezer side at this point.

[Cpt Mark]

Originally Posted by botanybay

Thanks for looking at the valves! I am very curious if both the fridge and freezer are using the same valves.

Is that an R12 system?

Are you reusing the holding plates or would they be available? As noted one of my plates failed some years ago and I am running just the freezer side at this point.

I've been sick for 2 weeks now. Still have a stupid cough and am tired so got nothing done today. I will be doing my best to get t done tomorrow tho.

It is an R12 system that worked awesomely until all the gas leaked out. The exception was the thermostat on the freezer. I had 2 separate compartments, one fridge, 1 freezer each with their own thermostat. The refer side worked fine but the freezer side would only come on/off when the fridge did.

I have 2 holding plates, the compressor and the fan unit with salt water cooling. I'm sure there's a monetary value to it but am happy to pack it all up and send it to you for the cost of shipping rather than throw it in the landfill.

[botanybay]

I sent a PM, definitely interested in some parts!