Electric Heating Sequence Of Operations; Electric Heat Operation Errors; Gas Heating Sequence Of Operations; Ignition Control Board - York ZF Series Installation Manual

5326602-XIM-B-1019

Electric Heating Sequence Of Operations

The following sequence describes the operation of the electric
heat section.
Two-stage heating:
a. Upon a call for first stage heat by the thermostat, the
heater relay (RW1) will be energized. After completing
the specified fan on delay for heating, the UCB will
energize the blower motor. If the second stage of heat is
required, heater relay (RW2) will be energized. After
completing the specified fan on delay for heating, the
UCB will energize the blower motor.
b The thermostat will cycle the electric heat to satisfy the
heating requirements of the conditioned space.

Electric Heat Operation Errors

Temperature Limit
If the UCB senses zero volts from the high temperature limit,
the indoor blower motor is immediately energized.
This limit is monitored regardless of unit operation status, i.e.
the limit is monitored at all times.
If the temperature limit opens three times within one hour, it will
lock-on the indoor blower motor.
Safety Controls
The UCB monitors the temperature limit switch of electric heat
units.
The control circuit includes the following safety controls:
Limit Switch (Ls)
This control is located inside the heater compartment and is set
to open at the temperature indicated in the Electric Heat Limit
Setting Table 32. It resets automatically. The limit switch
operates when a high temperature condition, caused by
inadequate supply air flow occurs, thus shutting down the
heater and energizing the blower.
Table 29: Electric Heat Limit Setting
UNIT (TONS) VOLTAGE
10, 12.5
10, 12.5
10, 12.5
10, 12.5
Reset
Remove the call for heating by lowering the thermostat setting
lower than the conditioned space temperature.
48
HEATER LIMIT SWITCH
kW OPENS °F
18
24
380/415
34
54

Electric 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 temperature within the
conditioned space. Refer to Table 30 for the required electric
heat anticipator setting.
Table 30: Electric Heat Anticipator Setpoints

Gas Heating Sequence Of Operations

When the thermostat calls for the first stage of heating, the low-
voltage control circuit from "R" to "W1" is completed. 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 by monitoring the Gas Valve (GV). Once voltage has
been sensed at the GV, the UCB will initiate the fan on delay for
heating, energizing the indoor blower the specified delay has
elapsed.
When the thermostat has been satisfied, heating calls are
ceased. The GV is immediately closed. The blower is de-
energized after the fan off delay for heating has elapsed. The
draft motor performs a 30-second post purge.

Ignition Control Board

First Stage Of Heating
When the ICB receives a call for first stage of heating, "W1," the
draft motor is energized. Once the draft motor has been proven,
a 30-second purge is initiated. At the end of the purge, the GV
is opened, and the spark igniter is energized for 10 seconds.
The ICB then checks for the presence of flame. If flame is
detected, the ICB enters a flame stabilization period. If flame
was not detected, the GV closes, and a retry operation begins.
During the flame stabilization period, a loss of the flame for 2
seconds will cause the GV to close and the retry operation to
begin. After the flame stabilization period, a loss of flame for 3/4
second will cause the GV to close and the retry operation to
begin.
150
At the conclusion of the flame stabilization period, the ICB will
150
operate the gas heat in high fire for an additional 60 seconds
150
(for a total for 120 seconds of high fire operation). After this 60
130
seconds, the ICB will then use the call for the second stage of
heat to control second stage operation of the GV.
When "W1" is satisfied, both valves are closed.
Second Stage Of Heating
When the ICB receives a call for the second stage of heating,
"W2," the ICB conducts a complete first stage ignition
SETTING, AMPS
W1
0.13
Johnson Controls Ducted Systems
W2
0.1