Operation
The following sections describe the sequences of
operation for the units.
Cooling sequence of operation
Compressor Operation
About this task:
2 Stage Cooling
This section assumes Free Cooling is not available.
1. Compressors are controlled by the Y1 through
Y2 thermostat inputs. If the Lead/Lag function
is turned OFF, a Y1 input energizes the C1
output. Thermostat Input into Y2 energizes
the C2 output respectively.
2. The FAN output for indoor fan operation
energizes with any cooling output after the
Fan On Delay for Cool expires.
3. A 30 second interstage delay occurs when
multiple stages are requested. When the
thermostat cooling inputs are lost and the
minimum runtime expires, the compressor
outputs stage off.
Note: A Y2 input without a Y1 input
energizes C1 first and then C2 30 s later.
4 Stage Cooling
This section assumes Free Cooling is not available.
1. Compressors are controlled by the Y1 through
Y4 thermostat inputs. Y1 input energizes the
C1 output. A Y2 input energizes the C3 output.
A Y3 input de-energizes the C3 output and
energizes the C2 output. A Y4 input energizes
the C3 output.
Note: For all models, the C1 output
energizes the first of the tandem
compressors and the C3 output
energizes the second of the tandem
compressors.
2. The FAN output for indoor fan operation
energizes with any cooling output after the
Fan On Delay for Cool expires.
3. A 30-s interstage delay occurs when multiple
stages are requested. Compressor minimum
off times are enforced while staging up and
down. When the thermostat cooling inputs
are lost and the minimum runtime expires,
the compressor outputs stage off.
4. Staging down sequence:
- Y1, Y2, Y3, Y4 – C1, C2, C3
- Y1, Y2, Y3 (Y4 off) – C1, C2 (C3 off)
- Y1, Y2 (Y3 off) – C2 (C1 off)
- Y1 (Y2 off) – C1 on (C2 off)
- All thermostat signals off – all stages
off
Gas heat sequence of operation
1. Heating stages are controlled by the W1
through W2 thermostat inputs. A W1 or W2
input energizes a H1 or H1/H2 output.
2. When the pre-ignition process is complete the
ignition module energizes the gas valve and
provides a 24 V input to the MV terminal on
the UCB.
3. The FAN ON HEAT DELAY timer starts as soon
as 24 V is present on MV terminal. When
the timer expires the FAN output for the
indoor fan operation energizes. If 24 V is not
received on the MV terminal within 6 min, an
alarm appears and the fan output energizes
immediately and remains On until the alarm
clears.
4. When the thermostat heat inputs are lost and
the 120 s Minimum Heat Run Timers have
expired, heating outputs stage off. The FAN
OFF HEAT DELAY timer starts when 24 V is
removed from the MV terminal. When the
timer expires, the FAN output for the indoor
fan operation de-energizes.
Note: If 24 V is lost on the MV terminal
during the same heat cycle, an alarm
appears and the fan output energizes
and remains On until 24 V is present
again on the MV terminal.
Installation Manual: YORK
®
Sun
™
Select YV28 to YV50
84
Johnson Controls Ducted Systems
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