Page 78 IM-738
3. If the fans are equipped with optional spring isolators,
check the fan spring mount adjustment. When the fans are
running they should be level. Refer to “Spring Isolated
Fans” on page 48.
4. Verify the rotation is correct.
5. Verify the DHL safety is opening at a pressure compatible
with duct working pressure limits.
Note: The supply and return fan drives are usually selected
for operation in the drive's midspeed range. The
return fan drives are usually shipped with fixed pitch
sheaves that will provide the selected fan speed; how-
ever, the supply fan drives are usually shipped with
variable pitch sheaves that are adjusted to provide the
minimum fan speed. Both drives should be adjusted
for proper airflow during air balancing. For more
information, refer to “Air Balancing” on page 80.
Economizer Start-up
1. Check whether the outdoor air is suitable for free cooling
by displaying keypad menu 9. "Low" indicates low out-
door air enthalpy; "High" indicates high outdoor air
enthalpy.
Refer to “Enthalpy Control” on page 62 to verify that the
enthalpy changeover control is working properly. You may
want to take temperature and humidity measurements.
2. Verify that switches PS1 and PS2 are at "off." This will
prevent compressor operation during the procedure.
3. At the keypad, set the cooling setpoints low enough so
that the controller will call for cooling. On CAV-ZTC
units, adjust the "Cooling Spt =" entry on menu item 12C.
On VAV or CAV-DTC units, adjust the "Cooling Spt ="
entry on menu item 12B and the "Setpoint=" entry on
menu item 13A.
4. Place the unit into the "Occ-Cool Only" mode through
keypad menu 11 ("Control Mode").
5. Observe the outdoor air dampers:
If the outdoor air enthalpy is low, the Step-and-Wait algo-
rithm should modulate the dampers open.
If the outdoor air enthalpy is high, the dampers should main-
tain their minimum position. Set the "Mm Airflow=" entry
on menu item 21A to some other value. Verify that the damp-
ers move toward the new minimum position setpoint.
6. If the unit is equipped with the electromechanical enthalpy
changeover control (Honeywell H205) and the outdoor air
is borderline, attempt to change its input to the MicroTech
II controller by turning the switch to "A" or "D". Check
menu 9. If the changeover occurred, go to step 5.
Note: It may not be possible to check the economizer oper-
ation in both low and high enthalpy states on the
same day. If this is the case, repeat this procedure on
another day when the opposite outdoor air enthalpy
conditions exist.
Compressor Start-up
With the supply and return fans operational, prepare for com-
pressor operation.
The unit is shipped with refrigeration service valves closed.
Backseat (open) the discharge, and liquid line valves. Con-
nect service gauges and crack the valves off the backseat
position (one turn forward). Verify that the unit has not lost
its refrigerant charge.
Scroll compressors only compress in one rotational direction.
Three phase compressors will rotate in either direction
depending upon phasing of the power to L1, L2 and L3.
Since there is a 50/50 chance of connecting power to cause
rotation in the reverse direction, it is important to verify the
compressor rotates in the proper direction after the system is
installed. If the compressor is rotating properly, suction pres-
sure will drop and discharge pressure will rise when the com-
pressor is energized. If the compressor is rotating in reverse,
the sound level is louder and current draw is substantially
reduced. After several minutes of operation, the compressor’s
internal protector will trip.
All three-phase compressors are internally wired the same.
Therefore, once the correct phasing is determined for a spe-
cific system or installation, connecting properly phased
power leads to the same terminals should maintain proper
rotation direction.
Verify that the crankcase heaters are operating. These should
operate for at least 24 hours before starting the compressors.
Verify that the condenser fan blades are positioned properly
and that the screws are tight (See Figure 85). The fan blade
must be correctly positioned within its orifice for proper air-
flow across the condenser coils.
CAUTION
Adjust dampers properly. Improper adjustment may
damage the dampers.
When an economizer is ordered without an actuator, the
linkage requires a 3.14" linear stroke to fully open it. Do
not allow dampers to be driven beyond their normal full
closed or full open position.
WARNING
Low ambient temperature hazard. Can cause
compressor damage.
Do not attempt to start up and check out the refrigeration
system when the outdoor air temperature is below 50°F
unless the unit is specially equipped for low ambient
operation.
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