Quantech QTC40160, Installation Operation & Maintenance, Page: 114 / 188

Quantech
114
Section 7 - Operation
Form QTC4-NM2
Issue date: 05/12/2023
Low economizer superheat fault
The Low Economizer Superheat Fault is to protect
against excessive liquid refrigerant carryover from the
economizer in cases, which may be a result of the EEV,
Sensor or other problems. It also protects the system
compressor from liquid refrigerant flood back from the
economizer feed line if the economizer valve fails to
close.
The safety is ignored for the first 10 min of operation
if the system economizer feed valve is closed (0%) and
for 5 min of operation if the economizer feed valve is
open greater than 0%. If the discharge superheat falls
below 5.0°F (2.8°C) for 5 min under either condition,
the system sutsdown.
The X indicates the system and YYYYYYY indicates
the system is in a FAULT condition and will restart
when the 120 s anti-recycle timer times out or LOCK-
OUT and does not restart until the operator clears the
fault using the keypad.
Discharge pressure load limiting/unloading
Discharge pressure load limiting protects the condens-
er from experiencing dangerously high pressures. A
system is permitted to load normally as long as the dis-
charge pressure is below the High Discharge Pressure
Cutout minus 20 psig. Between Cutout minus 20 psig
and Cutout minus 15 psig loading is inhibited even
though increased loading may be required. Between
Cutout minus 15 psig and the Discharge Pressure Cut-
out, forced unloading is performed every 2 s according
to the following table.
The discharge pressure unload point is fixed at 255
psig.
Table 22 -
Discharge pressure load limiting/unloading
Discharge pressure Unloading
Discharge pressure cutout - 20 psig and
discharge pressure cutout - 15 psig
0 Hz
Discharge pressure cutout - 13.5 psig 1 Hz
Discharge pressure cutout - 12 psig 2 Hz
Discharge pressure cutout - 10.5 psig 3 Hz
Discharge pressure cutout - 9 psig 4 Hz
Discharge pressure cutout - 7.5 psig 5 Hz
Discharge pressure cutout - 6 psig 6 Hz
Discharge pressure cutout - 4.5 psig 7 Hz
Discharge pressure cutout - 3 psig 8 Hz
Discharge pressure cutout - 1.5 psig 9 Hz
Discharge Pressure Cutout - 0 psig 10 Hz
Suction pressure load limiting/unloading
Suction pressure load limiting helps to protect the
evaporator from freezing. A system is permitted to load
normally as long as the Suction Pressure is above the
Suction Pressure 2.6 psig. Between Suction
Pressure 2.6 psig and the Suction Pressure
1.7 psig, loading is inhibited, even though in-
creased loading is required.
Between the Suction Pressure 1.7 psig and
"Suction Pressure Cutout", forced unloading is per-
formed every 2 s according to Table 23 on page 114 .
This situation would occur if the suction pressure cut-
out transient override control is in effect. See
Low suc-
tion pressure cutout (software) fault on Page 112 . The
suction pressure cutout is programmed under the PRO-
GRAM key. The default Suction Pressure Cutout is set
at 26.1 psig.
Suction pressure load limiting is active at startup, to
only prevent loading of the compressors. Suction pres-
sure limit unloading will not occur until the system run
time reaches 5 min of operation to allow the system to
stabilize.
Table 23 - Suction pressure load limiting/unloading
R-134a
Suction pressure
Unloading
Suction pressure is between
2.60 psig and
1.70 psig
0 Hz
Suction pressure 1.53 psig 1 Hz
Suction pressure 1.36 psig 2 Hz
Suctio ut +1.19 psig 3 Hz
Suction pressure 1.02 psig 4 Hz
Suction pressure 0.85 psig 5 Hz
Suction pressure 0.68 psig 6 Hz
Suction pressure 0.51 psig 7 Hz
Suction pressure 0.34 psig 8 Hz
Suction pressure 0.17 psig 9 Hz
Suction pressure cutout 10 Hz