Table 19 - Discharge Pressure Load Limiting/Unloading; Table 20 - Suction Pressure Load Limiting/Unloading - York YVAA Installation Operation & Maintenance

Form 201.47-ICOM1
Issue date: 17/11/2022
The safety is ignored for the first 10 minutes of op-
eration if the system economizer feed valve is closed
(0%) and for 5 minutes of operation if the economizer
feed valve is open greater than 0%. If the discharge su-
perheat falls below 2.8°C (5.0°F) for 5 minutes 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 second anti-recycle timer times out or
LOCKOUT 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 seconds ac-
cording to the following table.
The discharge pressure unload point is fixed at 255
psig.

Table 19 - Discharge pressure load limiting/unloading

Discharge pressure
Discharge Pressure Cut-
out- 20 psig and Discharge
Pressure Cutout- 15 psig
Discharge Pressure Cutout- 13.5 psig
Discharge Pressure Cutout- 12 psig
Discharge Pressure Cutout- 10.5 psig
Discharge Pressure Cutout- 9 psig
Discharge Pressure Cutout- 7.5 psig
Discharge Pressure Cutout- 6 psig
Discharge Pressure Cutout- 4.5 psig
Discharge Pressure Cutout- 3 psig
Discharge Pressure Cutout- 1.5 psig
Discharge Pressure Cutout- 0 psig
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 Cutout + 2.6 psig. Between Suction
Pressure Cutout + 2.6 psig and the Suction Pressure
JOHNSON CONTROLS
Cutout + 1.7 psig, loading is inhibited, even though in-
creased loading is required.
Between the Suction Pressure Cutout + 1.7 psig and
"Suction Pressure Cutout", forced unloading is per-
formed every 2 seconds according to Table 20 on page
117. This situation would occur if the suction pres-
sure cutout transient override control is in effect. See
Low Suction Pressure Cutout (Software) Fault on Page
115. The suction pressure cutout is programmed un-
der the PROGRAM 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 minutes of operation to allow the sys-
tem to stabilize.

Table 20 - Suction pressure load limiting/unloading

Suction Pressure is between
"Cutout +2.60 psig" and
"Cutout +1.70 psig"
Suction Pressure Cutout+1.53 psig
Suction Pressure Cutout+1.36 psig
Suction Pressure Cutout+1.19 psig
Suction Pressure Cutout+1.02 psig
Suction Pressure Cutout+0.85 psig
Unloading
Suction Pressure Cutout+0.68 psig
0 Hz
Suction Pressure Cutout+0.51 psig
Suction Pressure Cutout+0.34 psig
1 Hz
Suction Pressure Cutout+0.17 psig
2 Hz
Suction Pressure Cutout
3 Hz
4 Hz
5 Hz Suction Pressure is between
"Cutout +2.70 psig" and
6 Hz
"Cutout +1.80 psig"
7 Hz
Suction Pressure Cutout+1.62 psig
8 Hz
Suction Pressure Cutout+1.44 psig
9 Hz
Suction Pressure Cutout+1.26 psig
10 Hz
Suction Pressure Cutout+1.08 psig
Suction Pressure Cutout+0.90 psig
Suction Pressure Cutout+0.72 psig
Suction Pressure Cutout+0.54 psig
Suction Pressure Cutout+0.36 psig
Suction Pressure Cutout+0.18 psig
Suction Pressure Cutout
SECTION 7 - OPERATION
R-134a
Suction pressure
R-513A
Suction pressure
7
Unloading
0 Hz
1 Hz
2 Hz
3 Hz
4 Hz
5 Hz
6 Hz
7 Hz
8 Hz
9 Hz
10 Hz
Unloading
0 Hz
1 Hz
2 Hz
3 Hz
4 Hz
5 Hz
6 Hz
7 Hz
8 Hz
9 Hz
10 Hz
117