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After the system has been leak checked and proven sealed, connect the vacuum
pump and evacuate system to 500 microns. The vacuum pump must be connected
to both the high and low sides of the system through adequate connections. Use
the largest size connections available since restrictive service connections may lead
to false readings because of pressure drop through the fittings.
IMPORTANT: Compressors (especially scroll type) should never be used to evacu-
ate the heat pump system because internal electrical arcing may result in a dam-
aged or failed compressor.
10.0 START UP AND PERFORMANCE
Even though the unit is factory-charged with Refrigerant-22 (R-22), the charge must
be checked to the charge table on the service panel and adjusted, if required. (See
Table 1.) Allow the unit to run for a minimum of five minutes. Before analyzing
charge, see the instructions on the unit service panel rating plate for marking the
total charge.
11.0 CHECKING AIRFLOW
The air distribution system has the greatest effect on airflow. The duct system is
totally controlled by the contractor. For this reason, the contractor should use only
industry-recognized procedures.
Heat pump systems require a specified airflow. Each ton of cooling requires
between 350 and 450 cubic feet of air per minute (CFM), or 400 CFM nominally.
Duct design and construction should be carefully done. System performance can be
lowered dramatically through bad planning or workmanship.
Air supply diffusers must be selected and located carefully. They must be sized and
positioned to deliver treated air along the perimeter of the space. If they are too
small for their intended airflow, they become noisy. If they are not located properly,
they cause drafts. Return air grilles must be properly sized to carry air back to the
blower. If they are too small, they also cause noise.
The installers should balance the air distribution system to ensure proper quiet air-
flow to all rooms in the home. This ensures a comfortable living space.
An air velocity meter or airflow hood can give a reading of the system CFM's.
12.0 CHECKING REFRIGERANT CHARGE
Charge for all systems should be checked against the Charging Chart inside the
access panel cover.
IMPORTANT: Do not operate the compressor without charge in system.
Addition of R-22 will raise pressures (vapor, liquid and discharge).
If adding R-22 raises both vapor pressure and temperature, the unit is overcharged.
IMPORTANT: Use industry-approved charging methods to ensure proper system
charge.
12.1 CHARGING BY LIQUID PRESSURE
Liquid pressure method is used for charging systems in the cooling and heating
mode. The service port on the liquid service valve (small valve) and suction (large
valve) is used for this purpose.
Verify that the outdoor unit is running and the indoor air mover is delivering the
maximum airflow for this system size. Read and record the outdoor ambient tem-
perature. Read and record the liquid and suction pressures at the ports on the liquid
and suction valves. If refrigerant lines are sized using the nameplate charge, the
correct liquid pressure is found at the intersection of the suction pressure and the
outdoor ambient.
1. Remove refrigerant charge if the liquid pressure is above the chart value.
2. Add refrigerant charge if the liquid pressure is below the chart value.
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Troubleshooting
