COOLING SYSTEM
The cooling section is a complete factory package utilizing an
air-cooled condenser. The system is factory-charged with
Refrigerant-22.
The compressor is hermetically sealed and internally sprung.
The compressors have inherent (internal) protection. If there is
an abnormal temperature rise in the compressor, the protector
will open to shut down the compressor.
PRELIMINARY OPERATION COOLING
After the installation has been completed, energize the
crankcase heater (3 ton only) for at least 4 hours before
operating the unit. After this initial warm-up, the compressor
should be given three false starts (energized just long enough
to make a few revolutions) with a 5 minute delay between each
start before being put into full time service.
NOTE: Prior to each cooling season, the crankcase heater (3
ton only) must be energized at least 10 hours before
the system is put into operation.
COOLING SEQUENCE OF OPERATION
Single-Stage Cooling: When the thermostat calls for “cooling”,
“R” is closed to “G” and “Y1" (wiring schematic) which
completes the low voltage control circuit, immediately
energizing the compressor, condenser fan motor and blower
motor simultaneously.
Two-Stage Cooling: A two-stage cooling thermostat may be
used if the unit has an economizer. First-stage cooling is
provided by the economizer - if the outdoor air enthalpy is
acceptable, and second-stage cooling is provided by the
compressor. Jumper wire J1 must be removed. Refer to the
unit wiring diagram.
After the thermostat is satisfied and opens, the blower will
continue to run for a short time. All other components will stop.
CONTINUOUS BLOWER - Continuous blower operation is
possible by closing the R to G circuit on the thermostat.
SAFETY CONTROLS (Cooling)
The refrigerant system is equipped wth the following safety
controls:
1. A Suction Line Freezestat to protect against low evapora-
tor temperature due to low air flow or a low return air tem-
perature.
2. AHigh Pressure Cutout Switch to protect against excessive
discharge pressures due to a blocked condenser coil or a
condenser motor failure.
3. A Low Pressure Switch to protect against loss of refrigerant
charge.
If neither one of the above safety controls opens, the refrigerant
system will be locked out. The lock out of the system can be
reset by opening the 24V circuit either at the room thermostat
or at the unit disconnect.
HEATING SEQUENCE OF OPERATION
The following sequence describes the operation of the gas
heat section.
CONTINUOUS BLOWER: With the room thermostat switch
set to “ON”, the supply air blower will operate continuously. The
normally closed blower interlock relay contact “K3-1" provides
24 volt power to the blower relay ”BR". The “BR” power
contacts close and the blower motor operates.
INTERMITTENT BLOWER: With the room thermostat system
switch set to the “AUTO” or “HEAT” position and the fan switch
set to “AUTO”, the supply air blower will operate after the room
thermostat calls for heat and the air in the gas heat
compartment has achieved a pre-set temeprature.
When “TH1" on the thermostat closes, the draft motor relay
”DMR" or “DMC” is energized. The “DMR” or “DMC” power
contacts close which energizes the line voltage draft motor. As
the speed of the draft motor reaches approximately 2500 RPM,
the centrifugal switch contact “CS” located on the end of the
draft motor shaft closes to power the ignition control “IC”.
After 15 seconds the “IC” will start the ignitor sparking and will
open the redundant valve locted inside the main gas valve
“GV” to allow a flow of gas to only the carryover tube. See
Figure 10. Only after the pilot flame has been ignited and the
presence of pilot flame detected at the “IC” by a signal sent
back through the flame sensor is sparking terminated and the
main gas valve opened.
Gas flows into each of the main burners and is ignited from the
carryover tube flame.
The “IC” will try for 85 seconds to ignite the pilot carryover tube.
If the “IC” fails to detect a pilot flame during the 85 seconds, it
will close the redundant valve. After a 5 minute purge period,
the “IC” will again try to light the pilot carryover tube. This will
continue continuously until the “IC” detects a pilot flame.
If, after detecting a pilot flame and opening the main gas valve,
the “IC” looses pilot flame indication, it will close both the main
and redundant gas valves. The “IC” will start the above
sequence over until a pilot flame is detected and it will open the
main gas valve again.
The “IC” will only allow 16 pilot flameouts and a single rollout
switch opening per thermostat cycle. After 16 pilot flameouts or
a single rollout switch opening, the “IC” closes both the main
and redundant gas valves. The “IC” requires resetting the
thermostat or removal of it's power lead coming from the draft
motor to reset the “IC” and return it to the above sequence of
operation.
At the same time power was supplied to the “DMR” or “DMC”, a
parallel circuit activates the time delay relay “BT” or “ETD”. The
“BT” or “ETD” closes in approximetly 35 seconds and starts the
circulating air blower by energizing the blower interlock relay
“K3", thus closing the ”K3-2" contact and energizing the blower
relay “BR”.
When the heating cycle is complete, “TH-1" opens de-
energizing the “IC”, thus closing the redundant and main gas
valves. The blower motor and the draft motor continue to run
for a short period after the furnace is shut down until the “BT” or
“ETD” opens (in approximately 25 seconds) de-energizing the
“K3", ”BR" and “DMR” or “DMC” relays.
Unitary Products Group
13
035-14832-003-A-0204
OPERATION
GAS
VALVE
GAS MAIN
MAIN VALVE
TO MAIN
BURNER
REDUNDANT
VALVE
TO PILOT BURNER
FIG. 10
- GAS VALVE PIPING
