Adjusting Superheat On Two Circuit Holding Plate System


Freezer
TXV Valve Setting		 Time Inlet Plate 1
Degrees F		 Plate 1 (coldest)
Degrees F		 Exit Plate 1
Degrees F		 Plate 2 (Coldest)
Degrees F		 Exit Plate 2
Degrees F
Fully CCW 0630 +2F +6F 0F -1F -2F
CW 1/4 0645 +5-6F +5-6F 0F +1.8F +1.8F
CW 2/4 0715 -2.2F +6F +1.2F -2.3F -3F
0720 -3F +1.8F -3.3F -5.6F -5.8F
0735 -2.2F -1.6F -4.6F -6.4F -6.1F
CW 3/4 0755 -5.7F -3.6F -7.5F -8F -9F
0805 -3.3F -3.4F -6.5F -8F -7F
CW 4/4 0820 -4.7F -3.4F -7.2F -6F -5F
CW 5/4 0830 -6F -4F -7.2 -6F -5F
0955 -3.3F -2.4F -5F -8F -8F
CW 6/4 1030 -4.6F -2.7F -7F -11F -8F
CW 7/4 1050 -8F -5F -9F -12F -11F
CW 8/4 1110 -9F -5F -8F -12F -13F
CW 9/4 1125 -10F -8F -10F -12F -12.5F
CW 10/4 0215 -8F -8.5F -11.5F -14.5F -16F
CW 11/4 0645 -8F -10F -11.8F -16F -17F
CW 12/4 0815 -9.2F -9.2F -12F -15F -16F
CW 13/4 0840 -9.2F -9F -12.3F -15F -17F
CW 14/4 1115 -10.3F -10.2F -12.3F -17F -18F
CW 15/4 1130 -24F -12F -26F -26F -32F
1140 -27F -18F -31F -28F -21F
1155 -26F -18F -30F -30F -21F
1205 -30F -20F -32F -32F -24F
1320 -26F -22F -30F -32F -35F
1415 -28F -26F -31F -32F -35F
CW 16/4 1500 -10F -22F -10F -21F -14F
CW 15/4 1515 Kicked Off Jumpered On
1545 -20 -25 -27 -30 -36
1605 -37 -26 -22 -30 -22
1620 -24 -24 -18 -26 -18
1640 -16 -21 -17 -26 -18
CW 15/4 - 1/8 1650 -17.5 -22.5 -15 -27 -15
1705 -20 -26 -15 -26 -20
1805 -10 -20 -8 -20 -10
CW 15/4 1835 Kicked On Off shortly after  1805
1850 -9 -14 -4 -14 -4
CW 15/4 -1/8 1935 -20 -18 -25 -27 -24
2005 Kicked Off Jumpered On
2035 -25 -22 -31 -33 -36
2050 -25 -23 -31 -36 -37
2055 -25 -24 -31 -36 -37
2120 Kicked Off -23 -26
2300 -15 -16
2301 Kicked On


Thus, it appears that the correct setting is 14/4 + 1/8 = 29/8 = 15/4 - 1/8 = 3  5/8 turns = 3 3/4 minus 1/8. The setting is rather sensitive with a movement of an 1/8 making a significant difference. The goal is the minimum amount of "superheat" which allows the system to achieve temperatures in the range of -20F to -25F. All the way counter clockwise is the minimum amount of "superheat" being applied. Turning clockwise increases the "superheat" setting. Midrange for these valves is about 4 complete turns clockwise. So, start with the valve completely counterclockwise and keep turning it down by quarter turn incriments until the temperature is able to achieve very low values. Because increasing superheat reduces the flow of refrigerant this will slow down the heat transfer but allows lower expansion pressure and thus lower temperature. This is a delicate balance is is very sensitive to the specific system installation. The object is the minimum amount of "superheat" or minimum number of clockwise turns when the temperature goes to a low value.

Freezer Cut Off at various settings (3/29/2012)
Freezer Setting Plate 1 Temp Plate 2 Temp Bottom of Box Top of Box
1  (-2) +8F +18F
2  (0) -5F -5F +2.9F +6F
3  (1)
4  (2) -14F -12F -5F
5  (3)
6  (4)
7  (5) -8F +2F

Fridge Plate Pull down (Superheat setting is not nearly so sensitive as it is for freezer applications, it did get down to low temp but it might be faster with less superheat)
time Min Plate Temp Temp at Sensor Bulb
2105 29F 29F
2110 2.5F 29F
2120 -14.5F 26F
2130 -11F 26F
2150 -23F -1F
2215 -27F -20F
2255 -27F -23F
It looks like this plate was freezing at about 26F for some time until 2150 and then froze solid and rapidly got much colder. The goal for the system is to turn off that circuit once the plate freezes solid so the freezer can come down faster.

Plan is to get a recording temp device for both the fridge and freezer to allow setting the thermostats to turn off right after the plates are fully frozen (~26F for fridge and ~0F for freezer)