● 3. Use the toggle switches on the control Box to cool only one box at a time.
● 4. Turn the compressor on and watch the temperature displayed on the control. Start “
timing” when the temperature falls to 32
0
F / 0
0
C (for a refrigerator) and/or 10
0
F / -12
0
C (for
a freezer).
● 5. Continue to run the compressor for the correct period of time for that box (as
determined from the table).
● 6. After the correct time has elapsed, note the temperature displayed on the control.
This is the new “setpoint” setting (Note: on ECM controls the setting for “normal” mode is
“St 1").
● 7. After entering the new “setpoint”, determine the correct “differential” setting and enter
it. The correct “differential” setting is the difference between the new “setpoint”
temperature and +32
0
F (0
0
C) for the refrigerator or +10
0
F (-12
0
C for the freezer).
How Long Should Your System Run?
Your system run time is determined by (a) the hourly BTU capacity of your compressor, (b) the
size and quantity of holding plates and, (c) the type of box (ie. refrigerator or freezer). The
ambient temperature (heat load) is irrelevant as this only changes the “holdover time” (ie. the
time between compressor cycles). Compressor run time is determined individually for each box.
To calculate your run time for a particular box:
1. Add up the total capacity of the holding plate(s) in the box (be sure to differentiate
between refrigerator and freezer capacity).
2. Divide the total plate capacity (from #1 above) by the capacity of your compressor unit
(again - be sure to differentiate between refrigerator and freezer capacity).
3. The resulting number is the total number of hours your compressor will need to run
(for minutes, multiply by 60).
Holding Plate and Compressor Unit Capacities
Holding Plate Ref. Frz. Btu/hr Compressor Unit Ref. Frz.
M1 (11" x 16")* 1381 1030 51 Micro HPS 3680 1245
M2 (11" x 20")* 1842 1373 66
M3 (13" x 24")* 2720 2029 93
M4 (15" x 19")* 2354 1755 81
* Holding plate size includes the expansion valve.
For example:
To determine how long a Micro HPS compressor should run to freeze down two Trimline
tm
#3
holding plates in a freezer, add up the total capacity of the holding plates (2029 + 2029 =4058)
and divide the result by the compressor capacity (4058 /1245 = 3.25). Therefore, the correct run
time for a Micro HPS compressor freezing down two Trimline
tm
#3 freezer holding plates is 3.25
hours or 3 hours 15 minutes. This example is the longest run time required for the largest single
zone.
Method #2 - Charting The Cycle
For most cruisers the tuning method outlined above will be perfectly adequate. However, for
those technically minded individuals who want to delve more deeply into the principles behind
“precision tuning”, we suggest charting the plate cycle. There is no better way to get a picture of
exactly what is going on with the freeze/thaw cycle then to chart it. The easiest way to
accomplish this is by using a chart recording thermometer. These machines will draw charts
very similar to the ones shown below, allowing you to see exactly the results of your changes. If
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