Start the supply air blower motor. Adjust the resis- tances in both the supply and the return air duct sys- tems to balance the air distribution throughout the conditioned space. The job specifications may require that this balancing be done by someone other than the equipment installer.
To check the supply air CFM after the initial balancing has been completed:
1.Remove the two 5/16” dot plugs from the blower motor and the filter access panels shown in Figure 11.
2.Insert at least 8" of 1/4 inch tubing into each of these holes for sufficient penetration into the air flow on both sides of the indoor coil.
NOTE: The tubes must be inserted and held in a posi- tion perpendicular to the air flow so that veloc- ity pressure will not affect the static pressure readings.
3.Using an inclined manometer, determine the pres- sure drop across a dry evaporator coil. Since the moisture on an evaporator coil may vary greatly, measuring the pressure drop across a wet coil under field conditions would be inaccurate. To assure a dry coil, the compressors should be deac- tivated while the test is being run.
4.Knowing the pressure drop across a dry coil, the actual CFM through the unit can be determined from the curve in Pressure Drop vs. Supply Air CFM (Figure 13).
Failure to properly adjust the total system air quantity and static pressure can result in extensive system damage.
After readings have been obtained, remove the tubes and reinstall the two 5/16” dot plugs that were removed in Step 1.
NOTE:
| 0.5 |
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(IWG) | 0.4 |
| 036 | 048 | 060 |
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DROP | 0.3 |
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PRESSURE | 0.2 |
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| 0.1 |
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| 0 |
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| 1000 | 1500 | 2000 | 2500 | 3000 |
NOMINAL CFM
FIGURE 13 - PRESSURE DROP ACROSS COIL
OPERATION
SEQUENCE OF OPERATIONS OVERVIEW
For these units, the thermostat makes a circuit between “R” and “Y1” for the cooling cycle.
The call is passed to the unit control board (UCB), which then determines whether the requested opera- tion is available and, if so, which components to ener- gize.
For heating, the thermostat makes a circuit between “R” and “W1”. The UCB energizes the compressor and condenser fan allowing the unit to run in heating mode. A time / temperature control operates the defrost cycle.
If at any time a call for both heating and cooling are present, the heating operation will be performed. If operating, the cooling system is halted as with a com- pletion of a call for cooling. Heating always takes prior- ity.
COOLING SEQUENCE OF OPERATION
CONTINUOUS BLOWER
By setting the room thermostat fan switch to “ON,” the supply air blower will operate continuously.
Unitary Products Group | 27 |
