York D3CG090 Installation Instructions Manual Download

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The “TH1" closes, the draft motor relay ”DMR" is energized.
The “DMR” power contact closes which energizes the line
voltage draft motor. As the speed of the draft motor reaches
approximately 2500 RPM, the centrifugal switch contact
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 located inside the main gas valve
“GV” to allow a flow of gas to only the carryover tube. See
Figure 11. 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.

If “IC” 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 “IC” will soft lock out for 5 minutes. If the
pilot flame is not detected after 16 retries, then “IC” will hard
lock out the first stage furnace operation until 24V power is
removed from the module either at the unit or by resetting the
room thermostat.
At the same time power was supplied to the “DMR”, a parallel
circuit activates “TDR” which closes “TDR” after approximately
16 seconds and energizes “K5" which closes ”K5-2" and starts
the blower by energizing “3M”.

When “TH2" closes calling for second stage heating, it
energizes ”W2" on the gas valve “GV” directly.

When the heating cycle is complete, “TH-1" opens
de-energizing the ”DMR" and “IC”, thus closing the redundant
and main gas valves. The blower motor continues to run

(approximately 15 seconds after the furnace is shut down) until
“TDR” opens de-energizing the “K5" and ”3M" relays.

SAFETY CONTROLS

The control circuit includes the following safety controls:

1. Limit Control (LS). This control is located inside the heat

exchanger compartment and is set to open at the
temperature indicated in Table 10. It resets automatically.
The limit switch operates when a high temperature
condition, caused by inadequate supply air flow occurs,

thus shutting down the ignition control and closing the main
gas valve and energizing the blower.

2. Centrifugal Switch (CS). If the draft motor should fail, the

centrifugal switch attached to the shaft of the motor
prevents the ignition control and gas valve from being
energized.

3. Redundant Gas Valve. This valve is an integral part of the

main gas valve and is located up stream of the main gas
valve. Should the main gas valve fail in the open position
the redundant valve serves as a back up and shuts off the
flow of gas.

4. Flame Sensor Rod. This sensor rod is located on the far

side of the carryover tube. If the ignition control does not
receive a signal from the flame sensor indicating that the
pilot flame has ignited properly, the main gas valve will not
open. If the flame sensor fails to detect the pilot flame during
operation of the main burners, a signal is sent to the ignition
control to close the main gas valve.

5. Rollout Switch. This switch is located in the burner

vestibule. In the event of a sustained main burner flame
rollout, it shuts off the ignition control and closes the main
gas valve.

HEAT ANTICIPATOR SETPOINTS

It is important that the anticipator setpoint be correct. Too high
of a setting will result in longer heat cycles and a greater

temperature swing in the conditioned space. Reducing the
value below the correct setpoint will give shorter “ON” cycles
and may result in the lowering of the temperture within the
conditioned space.

PRE-START CHECK LIST

Complete the following checks before starting the unit.

Units

(Tons)

Capacity, MBH

Limit Control

Opens,

Input

Output

7-1/2, 8-1/2
7-1/2, 8-1/2

10, 12-1/2
10, 12-1/2

163
204
204
245