York YCSA 120 T, Technical Information

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Rotation of compressors
The control unit provides a FIFO type rotation, in which the
first compressor to start will also be the first to be turned
off.
Start sequence: C1, C2, C3, C4.
Off sequence: C1, C2, C3, C4.
HP prevent
When this function is enabled, the control unit attempts to
avoid blocking of the unit due to an excess of high pressure.
When said pressure reaches a preestabished value close to
the off value, the control increases the fan speed to a maxi-
mum (if in cool cycle), or decreases fan speed to a minimum
(if in heat cycle). If the operating pressure continues getting
closer to the HP Prevent value, the control turns off one com-
pressor of the affected circuit tandem. The parameters of this
function are accessible from the Condensation menu.
Defrost cycle
If the evaporating pressure of one of the systems remains
below the value set to start the defrost cycle, during an ac-
cumulated time equal to the period established as the delay
between defrosts, a simultaneous defrost of all the coils of
the unit is put into operation. This cycle will terminate once
the pressure value set as defrost off is reached, or after the
time period set as maximum cycle duration is over.
The defrost sequence is as follows: 1. Compressors are
turned off. 2. After 15 seconds, the 4-way valves are inverted.
3. After 45 seconds, the compressors are turned on with fans
off. 4. Once defrost is finalized, the compressors are turned
off. 5. After 15 seconds, the 4-way valves are inverted. 6. After
45 seconds, compressors and fans are turned on.
Control sensors: Pressure transducers B3 and B4.
Parameters used:
- Simultaneous defrost.
- Defrost start pressure.
- Defrost end pressure.
- Delay upon call for defrost.
- Maximum duration of defrost.
- Minimum duration of defrost.
- Compressor forced off time by cycle inversion.
- Delay of 4-way valve inversion.
Outputs affected:
- Compressors (N1, N2, N3 and N4).
- 4-way valves (N13 and N14).
- Fans (Y3 and Y4).
DefrOff Defrost end pressure
DefrON Defrost start pressure
D
t 1...3 Partial times in the defrost activation pressure zones
DefrAct Defrost active
t Time
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