Bulletin 30-020.007
Copyright © 2019 Unico Inc. Page 23
Figure 32. Measuring Plenum Static Pressure
In the absence of a manometer you can build a simple
but less accurate manometer in one of two ways. One
way is to use a short piece of ruler or yardstick and
clear plastic tubing as shown in Fig. 33.
Figure 33. U-Tube Manometer
CHARGING THE SYSTEM
DO NOT VENT REFRIGERANT TO THE
ATMOSPHERE!! It is a violation of federal law and
in some cases local ordinances also. Always use a
refrigerant recovery or recycling device.
If charging a heat pump, refer to Bulletin 30-024,
Instructions for "M" Series Modular Heat Pump
Systems. The following procedure is only valid for
charging the system during the cooling mode.
To check for proper charge record the refrigerant
pressures and temperatures. Check the refrigerant
charge by measuring the amount of sub-cooling (or
‘approach’ temperature for some condensing units). If
the outdoor manufacturer does not have sub-cooling or
“approach” temperature charts, then be sure that the
sub-cooling is at least between 3 and 8 °F (2 to 5°C).
For long refrigerant lines or when the evaporator is
above the condenser, the sub-cooling should be close
to 8°F; otherwise, aim for the low end of the range.
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