IM 1287-6 • REBEL APPLIED ROOFTOP 80 www.DaikinApplied.com
7. The compressor should operate continuously while there
is a call for cooling. If the compressor cycles on its low
pressure switch, due the following:
a. Verify that the circuit is not low on refrigerant.
b. Check for low supply airow.
c. Check for clogged lters.
d. Check for restricted ductwork.
e. Check for very low temperature return air entering
the unit.
f. Verify that the liquid line components, expansion
valve, and distributor tubes are feeding the
evaporator coil.
g. Verify that all air handling section panels are
closed.
h. Verify that the liquid line solenoid valves are
completely open (energized).
8. If the refrigeration circuit has multiple compressors, verify
that the compressors stage properly. As the circuit load
increases the second compressor (if available) will be
energized.
9. Verify that the condenser fans are cycling (ON/OFF)
and rotating properly (blowing air upward). When a
compressor starts, at least one condenser fan should
also start. MT4 should control the remaining condenser
fans based on ambient air conditions. Refer to the unit
wiring diagrams for control wiring.
10. After 15 minutes of run time, check the oil level in the
compressor sightglass (if available). If low oil or heavy
foaming is observed, it is possible that liquid refrigerant
is returning to the compressor. Check the suction
superheat It should be between 10°F (5.6°C) and 14°F
(7.8°C).
11. Place the unit into the “Fan Only” mode through the
keypad menu Main Menu\Quick Menu\Ctrl Mode = fan
only.
12. Check refrigerant circuit #2 by repeating steps 2
through 9.
13. Check the compressor oil level again. If oil level is low,
consult Technical Support before adding oil.
14. Verify that the condenser refrigerant subcooling for each
refrigeration circuit at full capacity is between as shown
in Table 13.
Table 13: Expected Subcooling for Compressor Start-up
Outdoor Air Temp. (F) Subcooling (F)
75-80 7-10
81-90 10-12
91-95 12-15
95-105 15-20
Expansion Valve Superheat Adjustment
(Thermal Expansion Valve)
Thermal Expansion Valve on Fixed Speed
Compressor Circuits
It is very important that the expansion valve superheat setting
be adjusted to be between 10°F (5.6°C) and 14°F (7.8°C).
Insucient superheat will cause liquid refrigerant ood back
to the compressor which may result in slugging. Excessive
superheat will reduce system capacity and shorten compressor
life.
Turn the adjustment stem clockwise to increase superheat.
Not exceeding one turn, adjust the stem and then observe the
superheat. Allow up to 30 minutes for the system to rebalance
at the nal superheat setting.
Electronic Expansion Valve on Variable Speed
Compressor Circuits
The electronic expansion valve superheat setting is preset from
the factory and does not require any eld adjustment.
Checking Superheat
Following are recommendations for checking superheat:
1. Close the unit section doors. Operating the unit with its
doors open will aect the expansion valve and system
operation considerably.
2. For units with one expansion valve per circuit, check the
pressure and temperature at the compressor suction
valve.
NOTE: If low oil level is accompanied by heavy foaming
visible in the oil sight glass, it is possible that excess
liquid refrigerant is returning to the compressor.
Check the suction superheat and adjust the
expansion valve for 10°F (5.6°C) and 14°F (7.8°C) of
superheat. If proper superheat is obtained, sight glass
foaming is not a concern.
Heating System Start-up
General
1. At the keypad, set the heating setpoints high enough so
that the controller calls for heating. Adjust the value in
Main Menu\ Commission Unit\Heating Set-Up\Occ Htg Spt
= above the Control Temp shown in the same menu. In
addition, on DAC units, adjust the DAT heating value in
Main Menu\Commission Unit\Heating Set-Up\ DAT Htg
Spt above the discharge temperature shown as Disch
Temp in the same menu.
2. Place the unit into heating mode through the keypad
menu Main Menu\quick Menu\Ctrl Mode = Heat Only.
3. Verify that the high ambient heat lockout temperature
setpoint, Main Menu\Commission Unit\Heating Setup\
Htg Hi OAT Lk is set above the current outside air
temperature (OA Temp) is shown in the same menu.
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