York DH 240 Installation Manual download pdf (Page 48)

129963-YIM-A-0605

48 Unitary Products Group

GAS HEATING SEQUENCE OF OPERATIONS

The following sequence describes the operation of the

gas heat section.

When the thermostat calls for the first stage of heating,

the low-voltage control circuit from "R" to "W1" and "G"

is completed, thru the UCB. The heat relay "RW1" is

energized. The "RW1-2" contacts close energizing the

draft motor control. The draft motor control contacts

close and start the draft motor. As the speed of the

draft motor reaches approximately 2500 RPM, the cen-

trifugal switch contact, located on the end of the draft

motor shaft, closes to power the first stage ignition

module "IC1", thru the "RW1-1 contacts.

Ignition module "IC1" will immediately start the first

stage igniter sparking and will open the redundant

valve located inside the first stage main gas valve

"GV1" to allow a flow of gas to only the first stage carry-

over tube. Only after the pilot flame has been ignited

and the presence of pilot flame detected at the "IC1" by

a signal sent back through the flame sensor is sparking

terminated and the first stage main gas valve opened.

Gas flows into each of the main burners and is ignited

from the carryover tube flame.

After completing the specified fan on delay for heating,

the UCB will energize the blower motor.

If "IC1" fails to detect a pilot flame, it will continue to try

for a maximum of 85 seconds to ignite the pilot tube. If

the pilot flame is not detected, then "IC1" will lock out

first stage furnace operation for five minutes or until

24V power is removed from the module either at the

unit or by resetting the room thermostat.

When the thermostat calls for the second stage of

heating, the low-voltage control circuit from "R" to "W2"

is completed, thru the UCB. Heat relay "RW2" is ener-

gized. The "RW2-1" contact is closed energizing the

second stage ignition module "IC2". "IC2" will immedi-

ately start the second stage igniter sparking and will

open the redundant valve located inside the second

stage main gas valve "GV2" to allow a flow of gas to

the second stage carryover tube. Only after the pilot

flame has been ignited and the presence of pilot flame

detected at "IC2" by a signal sent back through the

flame sensor is sparking terminated and the main gas

valve opened.

Gas flows into each of the second stage main burners

and is ignited from the carryover tube flame.

If "IC2" fails to detect a pilot flame, it will continue to try

for a maximum of 85 seconds to ignite the pilot tube. If

the pilot flame is not detected, then "IC2" will lock out

first stage furnace operation for five minutes or until

24V power is removed from the module either at the

unit or by resetting the room thermostat.

NOTE: That the second stage furnace can operate

even if first stage has locked out.

When the thermostat satisfies de-energizing the

"RW2"and "RW1", thus opening all gas valves. The

blower motor will continue to run after the furnace is

shut down until the specified fan off delay for heating

has been satisfied. The UCB will de-energize the

blower motor.

When the thermostat calls for the first stage of heating,

the low-voltage control circuit from "R" to "W1" is com-

pleted. A call for heat passes through the UCB to the

ignition control board (ICB). The UCB monitors the

"W1" call and acts upon any call for heat. Once voltage

has been sensed at “W1”, the UCB will initiate the fan

on delay for heating, energizing the indoor blower after

the specified delay has elapsed.

TABLE 24: ELECTRIC HEAT ANTICIPATOR

SETPOINTS

HEATER

VOLTAGE

SETTING, AMPS

TH1 TH2

208/230-3-60

0.29 -

36 0.29 0.29

54 0.29 0.58

72 0.29 0.58

460-3-60

0.29 -

36 0.29 0.29

54 0.29 0.29

72 0.29 0.29

575-3-60

0.29 -

36 0.29 0.29

54 0.29 0.29

72 0.29 0.29

FIGURE 17 - GAS VALVE PIPING

GAS

VALVE

GAS MAIN

MAIN VALVE

TO MAIN

BURNER

REDUNDANT

VALVE

TO PILOT BURNER

1 2 ... 43 44 45 46 47 48 49 50 51 52 53 ... 59 60

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York DH 240 Installation Manual Page 48

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