30 November 1998
open contacts of relay R-XX-03 prevent any signal from reaching current-to-pneumatic transducer
IP-XX-01. Thus, the dampers remain in their normal positions, with outside air and relief air dampers
closed and return air damper open.
(2) When the timeclock's occupied contacts close, relays R-XX-01 and R-XX-02 are energized,
and pilot light PL-XX-01 is turned on. The contacts of relay R-XX-02 energize the supply fan. The
auxiliary contacts of the supply fan starter energize relay R-XX-05 and, with the contacts of relay
R-XX-01, energizes pneumatic valve EP-XX-01, which allows the space temperature controller to control
cooling coil valve VLV-XX-02. Temperature setpoint device TSP-XX-01 provides the means for
adjusting the setpoint of space temperature controller TC-XX-01.
(3) When the ventilation delay contacts of timeclock CLK-XX-01 open to end the ventilation
delay mode of operation, relay R-XX-04 is de-energized and pilot light PL-XX-02 is turned off. The
contacts of relay R-XX-04, in series with the now closed but normally open contacts of relays R-XX-01
and R-XX-05, energize relay R-XX-03. The contacts of relay R-XX-03 connect the output signal of high
signal selector TY-XX-01 to current-to-pneumatic transducer IP-XX-01. The pneumatic output of
transducer IP-XX-01 places the dampers at minimum position unless relay R-XX-06 is energized.
Economizer controller EC-XX-01 controls the action of relay R-XX-06. The economizer receives signals
from outside air temperature transmitter TT-XX-01 and from return air transmitter TT-XX-02. The
difference between the return air temperature and the outside air temperature controls the DEV contacts,
and the return air temperature controls the PV contacts. When both these contacts are closed, relay
R-XX-06 is energized, and pilot light PL-XX-03 is turned on. The contacts of relay R-XX-06 close,
allowing the space temperature controller TC-XX-01 signal to modulate the dampers beyond minimum
(4) Space temperature proportional only controller TC-XX-01, with its temperature transmitter
TT-XX-03, on a rise in space temperature modulates the heating coil valve toward closed. On a further
rise in temperature, it modulates the outside air and relief air dampers from minimum position toward
fully open while modulating the return air damper toward closed. On a still further rise in temperature,
the cooling coil valve is modulated toward fully open. The reverse occurs on a fall in temperature.
Whenever the economizer controller de-energizes relay R-XX-06, the dampers revert to the minimum
position set on minimum position switch MPS-XX-01. At the conclusion of the occupied mode, relay
R-XX-01 is de-energized and, through its contacts, relay R-XX-03 is de-energized, closing the dampers;
pneumatic valve EP-XX-01 is de-energized closing cooling coil valve VLV-XX-02. Heating coil valve
VLV-XX-01 is always under the control of temperature controller TC-XX-01.
(5) On a fall in temperature to its setpoint, low temperature protection thermostat TSL-XX-01
opens its set of closed contacts in the supply fan circuit, de-energizing the supply fan. A set of open
contacts in low temperature protection thermostat TSL-XX-01 closes, energizing relay R-XX-07 and
lighting pilot light PL-XX-05. The contacts of relay R-XX-07 energize relay R-XX-09. One set of the
contacts of relay R-XX-09 locks in relay R-XX-09, and the other set de-energizes the supply fan. To
restart the fan after shutdown, both low temperature thermostat TSL-XX-01 and the control panel must
be manually reset. The control panel is reset by momentarily depressing manual switch HS-XX-02.
(6) When smoke detector SMK-XX-01 or smoke detector SMK-XX-02 detects the presence of
smoke, its normally closed contacts in the supply fan starting circuit open, de-energizing the supply fan.
The normally open contacts of the smoke detector(s) close, energizing relay R-XX-08 and lighting smoke
pilot light PL-XX-06. The contacts of relay R-XX-08 energize relay R-XX-09. One set of the contacts of