I tried to look back over the last the 155 posts to find answers to the following questions:
Why is the installation of heat exchanger being question?
What is causing the excessive high pressure on this system?
Who fabricated the holding plates?
What temperature are plate solutions set to freeze at? Plates Set to freeze at less than zero are difficult to freeze with 134a refrigerant.
What is the heat load of freezer box?
How much refrigerant is in this system?
When plates are frozen how long will plates stay frozen?
Refrigerant phase change at end of evaporator plates has happened, is there a chance test nitrogen may still be in system contaminating refrigerant.
How was it determined that there are no major restrictions to flow after TXV in low pressure side of system?
Chef, Someone suggested earlier to move sense bulb to line after freezer plates this may move refrigerant phase change back to freezer If not there could be a major blockage somewhere prior to refrigerator plates.
Having spent twenty years manufacturing more than hundred holding plates and selling engine drive boat refrigeration kits to amateur do it yourselfers I use a simple approach in trouble shoot plate system performance.
When servicing a new system add only one pound of refrigerant and start compressor then if suction pressure after start is less than 10 psi add refrigerant to achieve at least 10 psi. Because refrigerant sight glasses are not all the same I recommend that additional refrigerant to eliminate bubbles be avoided until frost is visible on exit line of last plate. When the small automotive receiver is used a full charge on most small systems is 2 to 3 pounds of refrigerant adding more than this only fluids seawater condenser.
The boating industry standards for one HP engine drive refrigerant piping was set by designs from Crosby, Grunert, Frigoboat and SeaFrost. All piping from TXV through plates was ½ in OD. Suction line piping from plates to compressor are either ½ inch OD or ½ inch ID. Crosby and Grunert both used heat exchangers between liquid and suction lines. Because seawater was used as a condenser cooling medium a manually operated seawater bypass was used to control super cooling if high side pressure was too low. Most condensers were oversized to allow for cruising in tropical waters. On system designed and sold in cool climates like Seafrost’s units or units from companies in the northwest refrigerant charges must be reduced or compressor needs to be operated at a lower rpm.
All of the above engine driven drive system seem to demonstrate the same pressures and temperatures as refrigerant is free to flow through normal phase changes. I was contracted to train six mechanics from three charter boat companies in the islands. In two weeks we boarded and tested around 40 boat engine drive refrigerators. Most systems were one holding plates some had two or three plates. Each units performance was measures by gauge pressures, plate freezing time and frost migration. On systems that performed well high pressure was between 135 and 120. Temperature of liquid line between filter/dryer and TXV was around 115 degree F. TXV temperature after 10 minutes running time was frosted and too cold to keep hand on. Light frost forming on line between plates on and two. Frost eventually was present on line leaving last plate. After plates were frozen compressor temperatures were cool. Suction pressure dropped to zero or 10 inches vacuum.
When you consider that the coils inside a holding plates are the same as coils in evaporator the only difference is in the heat absorption dynamics of eutectics solution is much slower than finned plate evaporators. If standard evaporators are efficient because the heat absorbing phase change occurs shortly after interring evaporator then TXV superheat must be effective in first holding plate. Years ago I had a open top holding plate on test stand and using a super heat bulb test chamber I am sure these tools are no longer available refrigerant was vented to cool bulb, I could monitor affects of superheat change on coils ice formation. If refrigerant phase change do not occur in the first plate that plate will not freeze.