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035-17480-000 Rev. A (800)

28

Unitary Products Group

INTERMITTENT BLOWER - COOLING

On cooling/heating thermostats with fan switch, when the fan
switch is set in the auto position and the thermostat calls for
cooling, a circuit is completed between the R, Y and G termi-
nals.

The motor is energized through the cool fan terminal and
runs on the selected speed. The fan off setting is fixed at 60
seconds for SEER enhancement.

HEATING OPERATIONAL SEQUENCE

Two-Stage Thermostat

In a typical system, a call for first stage heat is initiated by
closing the W1 thermostat contacts. The inducer blower is
energized at high speed and the control waits for the low
pressure switch contacts to close. The inducer blower is
energized at low speed and the 120 VAC silicon carbide
igniter is powered.

At the end of the igniter warm-up time, the first stage of the
two-stage gas valve is energized (low fire). Flame must be
detected within 7 seconds. If flame is detected, the delay-to-
fan-on period begins. After the delay-to-fan-on period ends,
the circulator fan is energized at low heat speed and the air
cleaner and humidifier are energized.

A call for second stage heat (W1 and W2) after a call for first
stage heat will energize the inducer at high speed and ener-
gize the circulator at high heat speed. The second stage
pressure switch contacts will close and energize the second
stage gas valve (high fire).

If a call for second stage heat occurs at the same time as a
call for first stage heat, the second stage heat is energized as
above.

When the second stage of the thermostat is satisfied, the
inducer motor is reduced to low speed and the second stage
gas valve is de-energized upon opening of the second stage
pressure switch contacts. The circulator remains on high heat
speed for 30 seconds and then is reduced to low heat speed.

When the first stage of the thermostat is satisfied, the gas
valve is de-energized and the heat delay to fan off begins tim-
ing. The inducer will post-purge for an additional 5 seconds,
then the inducer and humidifier will de-energize. Upon com-
pletion of the heat delay-to-fan-off, the circulator and air
cleaner are de-energized. The control timing is graphically
shown in Figure 29 on page 27.

If flame is not detected during the trial-for-ignition period, the
gas valve is de-energized, the ignitor is turned off and the
50A51 control goes into the retry sequence.

The retry sequence provides a 120-second wait with inducer
inter-purge following an unsuccessful ignition attempt (flame
not detected). After this wait, the ignition sequence is
restarted with an additional 10 seconds of ignitor warm-up

time. Two retries will be attempted before the control goes
into system lockout.

If flame is detected, then lost, the 50A51 control will repeat
the initial ignition sequence. After 5 attempts to sustain flame,
the control will go into system lockout.

If flame is established for more than 10 seconds after ignition,
the 50A51 controller will clear the ignition attempt (or retry)
counter. If flame is lost after 10 seconds, it will restart the igni-
tion sequence. This can occur a maximum of 5 times before
system lockout.

During burner operation, a momentary loss of power of 50
milliseconds or longer will de-energize the main gas valve.
When power is restored, the gas valve will remain de-ener-
gized and a restart of the ignition sequence will begin imme-
diately.

A momentary loss of gas supply, flame blowout, or a shorted
or open condition in the flame probe circuit will be sensed
within 0.8 seconds. The gas valve will de-energize and the
control will restart the ignition sequence.

Recycles will begin and the burner will operate normally if the
gas supply returns, or the fault condition is corrected, before
the last ignition attempt. Otherwise, the control will go into
system lockout.

If the control has gone into system lockout, it may be possible
to reset the control by a momentary power interruption of one
second or longer. Refer to the diagnostics section of this
instruction for reset information.

Single-Stage Thermostat

If a single stage thermostat is used the unit will be controlled
as above with the following exception. On a call for heat the
unit will operate on low fire as detailed above. If the heating
requirements cause the cycle to exceed 10 minutes, the high
fire timer will energize the second stage heat. The second
stage operation will function as detailed above. The heating
cycle will be completed in high fire operation.

Hot Surface Ignition System

Do not attempt to light this furnace by hand (with a
match or any other means). There may be a
potential shock hazard from the components of the
hot surface ignition system. The furnace can only
be lit automatically by its hot surface ignition
system.

Summary of Contents for P*XU/G9D-UP

Page 1: ...TART UP AND ADJUSTMENTS 20 ACCESSORY CONNECTIONS 24 FURNACE ACCESSORIES 25 FILTER PERFORMANCE 26 OPERATION AND MAINTENANCE 26 TROUBLESHOOTING 30 FURNACE CONTROL DIAGNOSTICS 30 WIRING DIAGRAM UPFLOW MO...

Page 2: ...THREE TWO PIPE SYSTEM USING COMBUSTION AIR FROM A VENTILATED ATTIC SPACE 18 HORIZONTAL VENT APPLICATIONS 18 CONDENSATE PIPING 19 SAFETY CONTROLS 19 START UP AND ADJUSTMENTS 20 IGNITION SYSTEM SEQUENCE...

Page 3: ...ransit There are no shipping or spacer brackets which need to be removed NOTES CAUTIONS WARNINGS The installer should pay particular attention to the words NOTE CAUTION and WARNING NOTES are intended...

Page 4: ...size as determined using the appropriate tables in Appendix G of the above codes SPECIFIC UNIT INFORMATION LIMITATIONS LOCATION This furnace should be installed in accordance with all national and lo...

Page 5: ...leaning Eighteen 18 inches at the side where access is required for passage to the front when servicing or for inspection or replacement of flue vent connections 8 Where it will not interfere with the...

Page 6: ...ust comply with the National Electrical Code NFPA 70 latest edition For altitudes above 2 000 ft reduce capacity 4 for each 1 000 ft above sea level Refer to Form 650 78 N1 1V Wire size based on coppe...

Page 7: ...ls NOTE In order to achieve the airflow indicated in the table it is recommended those applications over 1800 CFM use return air from two sides one side and the bottom or bottom only For single return...

Page 8: ...cation outside the utility room or basement For further details consult Section 5 3 Air for Combustion and Ventilation of the National Fuel Gas Code ANSI Z223 1 or CAN CGA B149 1 or 2 Installation Cod...

Page 9: ...for 63 F 35 C rise wire when installed in accordance with instructions Refer the rating plate or Physi cal and Rating Data Tables in these instructions for specific furnace electrical data Provide a p...

Page 10: ...mostat to the terminal board on the ignition module Connect Class 2 control wiring for single stage thermostat or for two stage thermostat Refer to Figure 7 for single stage and Fig ure 8 for two sta...

Page 11: ...e observed Long radius elbows are required for all units 1 Long radius elbows are required for all units 2 Elbows are assumed to be 90 degrees Two 45 degree elbows count as one 90 degree elbow 3 Elbow...

Page 12: ...e grade and anticipated snow depth 1 ft Above grade when adjacent to public walkway 7 ft From electric gas meters regulators and relief equipment min horizontal distance 4 ft Does not apply to multipl...

Page 13: ...ional Clearance FIGURE 12 Horizontal Termination Configuration With Horizontal Extension VENT OVERHANG COMBUSTION AIR ELBOW PARALLEL TO WALL 12 SEPARATION BETWEEN BOTTOM OF COMBUSTION AIR AND BOTTOM O...

Page 14: ...fined space is an area with less than 50 cubic feet per 1000 Btu hr input rating for all appliances installed in that area The following must be considered to obtain proper air for combustion and vent...

Page 15: ...all be permitted to be waived where special engineering approved by the authority having jurisdiction provides an adequate supply of air for combus tion ventilation and dilution of flue gases Combusti...

Page 16: ...nted vertical terminals may be field fabricated Standard PVC SRD fittings may be used Terminal configuration must comply as detailed in this section When selecting the locations for vent termination t...

Page 17: ...ater tight seal 7 Support the vent piping such that it is angled 1 4 per lin ear foot so that condensate will flow back towards the furnace Piping should be supported with pipe hangers to prevent sagg...

Page 18: ...Table 5 on page 16 Follow all notes installation procedures and required materials in the METHOD TWO ONE PIPE SYSTEM on page 14 to install the vent pipe from the unit to the outdoors VENT TERMINATION...

Page 19: ...quiva lent pipe be field installed as drain pipe The condensate piping may be tied together with the air conditioning con densate drain if the air conditioning condensate drain line is trapped upstrea...

Page 20: ...furnace the gas piping may be full of air In order to purge this air it is recommended that the ground union be loosened until the odor of gas is detected When gas is detected immediately retighten th...

Page 21: ...more accurate input rate adjustment To calculate a meter correction factor use the following formula Using the information from above calculate the gas input rat ing by multiplying the number of cubi...

Page 22: ...djustment 1 Turn off all electrical power to the system at main fuse or circuit breaker 2 Attach a manometer to the outlet pressure tap of the valve 3 Turn on power and energize main and redundant P M...

Page 23: ...crease the rise All direct drive blowers have multi speed motors The blower motor speed taps are located in the control box in the blower compartment Refer to Figure 28 and the unit wiring label to ch...

Page 24: ...ion of the circulating blower NOTE EAC and HUM power leads are provided in the junction box for easier installation FIGURE 27 Upflow Models P XU G9D UP Reading Gas Pressure GAS VALVE U TUBE MANOMETER...

Page 25: ...5 1075 1060 1045 1030 1000 960 910 830 755 LOW 805 795 785 770 755 730 700 655 615 565 80 75 1600 C HIGH 1940 1905 1870 1815 1760 1700 1620 1555 1460 1305 MED 1400 1390 1380 1370 1355 1320 1285 1255 1...

Page 26: ...urnace with 2 return openings and operating on high speed blower it is found that total sys tem static is 0 58 w c To determine the system airflow com plete the following steps 1 Obtain the airflow va...

Page 27: ...035 17480 000 Rev A 800 Unitary Products Group 27 FIGURE 29 Sequence Timing For 50a51 243 Control...

Page 28: ...eriod the gas valve is de energized the ignitor is turned off and the 50A51 control goes into the retry sequence The retry sequence provides a 120 second wait with inducer inter purge following an uns...

Page 29: ...l the filter simply reverse this procedure Lubrication Blower motors in these furnaces are permanently lubricated and do not require periodic oiling BLOWER CARE Even with good filters properly in plac...

Page 30: ...valves in the gas line to the furnace must be open 3 Make sure all wiring connections are secure 4 Review the sequence of operation Start the system by setting the thermostat above the room temperatur...

Page 31: ...used by a number of problems blocked vent or chimney faulty inducer cracked pressure switch hose 7 FLASH This fault code indicates that flame could not be established This no light condition occurred...

Page 32: ...NACE RELAY IGNITER GV GRD DOOR SWITCH N O SW ELEMENTARY DIAGRAM POWER SUPPLY 120 1 60 SEE NOTE 1 GRD DS C NO LS1 C 1LP COM 120V 24V SEC PRI 1T 40VA VENTOR MOTOR HSI NOTES LEGEND DOT DELAY ON TIMER FUS...

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