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C8-1 DIAGRAM WITH D5 DIAGRAM
Enthalpy High (outside air cannot be used for cooling):
17- Enthalpy control switches 1K and 2K internally.
18- Cooling demand is sent from A1 terminal C1 through enthalpy control terminals 1 and 2 and
through enthalpy control terminal 5 to energize the compressor and relays K37 and K55. The
compressor handles all cooling demand.
19- Contacts K37-1 close to energize blower on cooling speed. Simultaneously, contacts K55-1
switch (no affect). Blower is energized on cooling speed.
20- Blower demand energizes relay K3 in unit. Contacts K3-1 close to energize the blower and
contacts K3-2 close to energize the economizer. When 24VAC is applied between damper
motor terminal TR and TR1 outdoor dampers open to minimum position.
Night Setback (optional field installed)
21- Optional field installed time clock and night relay K11 must be connected for night setback op
eration.
22- Blower B3 operates only during a heating demand.
23- When clock contacts close, relays K11and K38 energize.
24- Contacts K38-1 close to energize setback resistor R4.
Contacts K38-2 close to energize setup resistor R5.
Contacts K38-3 open to energize blower B3 on demand only.
During night operation when contacts K38-3 are open. blower B3 operates only on demand
powered through relays K25 (for heat) or K37 (for cool). Outdoor air dampers are held closed
by contacts K11-2 (not shown) remaining open.
25- A1 terminal 1 feeds 20VDC at all times to A2 terminal 1 and contacts K38-1 and K38-2 (source
of voltage for resistors).
26- When heating demand is present during unoccupied periods, 20VDC feeds through K38-1
and R4. R4 alters the voltage. A2 terminal 6 receives that altered voltage and uses it to shift
the unoccupied setpoint. R4's value, 3.6K ohms, shifts the unoccupied setpoint down
10F. For example, if heat lever of A2 is set at 75F, the unoccupied setpoint for first stage
operation is 65F.
27- When cooling demand is present during unoccupied periods, 20VDC feeds through K38-2
and R5. R5 alters the voltage. A2 terminal 8 receives that altered voltage and uses it to shift
the unoccupied setpoint. R5's value, 1.2K ohms, locks out cooling in unoccupied mode.
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