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and "make" the circuit to, but not through, the first
stage gas valve. On propane units, with themocouple
energized, the pilot relay switch action makes the cir¬
cuit to gas valve.
4. Set the thermostat above room temperature. This
completes the circuit and energizes the gas valve.
5. Gas flows through the gas valve to the burners via
bypass where it ignites. If the conditioned space tem¬
perature continues to drop, the second stage of the
thermostat closes and opens the second gas valve
bringing the unit to full input.
With the furnace operating, make the following
checks:
The automatic pilot should turn the main gas off if
the pilot flame goes out.
Check this while the furnace is operating by shutting
off the pilot gas. The main burners should shutdown.
Allow the furnace to cool and the blowers to stop,
then check the upper limit switch.
Limit Control
The furnace is equipped with a lower and upper limit
control. When the lower limit opens, the first stage gas
valve is de-energized, shutting off the gas. The upper
limit control has a dual function; its primary action
is to shut off the first stage gas valve if the unit
overheats; as the gas valve is shut off, the fan delay
relay is energized, starting the blower. The upper
limit is a single pole double throw switch.
The recommended method for checking the limit con¬
trols is to gradually block off the return air after the
furnace has been operating for a period of at least five
minutes. As soon as the limit has proven safe, the
return air openings should be unblocked to allow nor¬
mal air circulation through the unit. Whether or not
the limit is functioning properly, and will "fail-safe"
in case of motor failure or overheating of the unit can
be determined using this method.
Fan Relay
The unit is equipped with a fan delay relay switch
located in the control box. When the observer faces
the control, the adjustment lever is moved upward to
lengthen
the
off cycle.
When
the
off cycle
is
lengthened, the on cycle is shortened automatically.
Reverse the process to shorten the off cycle.
Airflow and Temperature Rise
The temperature rise is the difference between the
temperature of the air in the return duct and that in
the discharge duct near the furnace. This temperature
rise, measured after equilibrium has been attained
(approximately five minutes), should be within the
range of 45°F to 75°F for Model 180-479 and 20°F to
50°F for Model 240-479.
An adjustable sheave on the blower motor pulley is
used to adjust the blower speed as follows:
CAUTION: Turn off electric power to unit before
removing or replacing blower belt. Proceed as follows.
r
1. Loosen the motor from the base and slide the
motor toward the blower housing. Remove the belt
from the blower.
2. Loosen the set screw in the movable flange of the
sheave. Screw the movable flange toward the fixed
flange to increase the blower speed, away from the
fixed flange to reduce the blower speed. Tighten the
set screw on one of the two flat surfaces on the pulley
hub.
Important: Increasing the blower speed will impose a
greater load on the blower motor. Do not exceed the
rated current draw of the motor.
3. Replace the belt and adjust for proper tension. The
belt should have approximately 1" sag under normal
finger pressure.
4. Check motor pulley and blower pulley for proper
alignment.
IX. COOLING OPERATION
Perform the following steps to check the cooling sec¬
tion for proper operation.
WARNING:
The
main
manual
gas
valve
for
both chillers must be closed for at least 5 minutes
before operating the cooling sections.
1. Be sure the manual gas valves for both chillers are
in the OFF position. Light pilots as described on In¬
struction Plate.
2. With the thermostat subbase switch levers on
COOL and AUTO, turn on both manual gas valves.
Set thermostat at its lowest setting. Make certain both
chillers are operating. To check for correct operation
of the electrical circuit; observe operation of gas valve
and solution pump of each chiller, all condenser fan
motors and the blower. Increase the setting of the
thermostat gradually until one chiller shuts off. Set
thermostat above room temperature and observe that
the other chiller shuts off.
3. Set thermostat subbase fan switch to ON and check
blower operation. The blower should run continually
with the thermostat set above or below room tem¬
perature.
4. To place the system in operation, replace all panels
and set thermostat at the desired temperature.
SEQUENCE OF OPERATION
(Cooling Section)
Both the 180-479 and 240-479 are equipped with two
stage cooling. Chiller No. 1 operates on the initial call
for cooling (single stage cooling). When additional
cooling is required, Chiller No. 2 is also activated
(two-stage cooling).
Refer in Figures 7 and 8. When the thermostat system
switch is in the COOL position and the fan switch is in
the AUTO position, the first stage cooling bulb in the
thermostat will close the circuit between terminals Yl
and R, and between terminals Yl and G when the
thermostat calls for cooling.
Closing the circuit between terminals Yl and G
energizes the blower relay (2A1) and closes its nor-
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8
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