Electric Heating Sequence Of Operations; Electric Heat Operation Errors; Temperature Limit; Safety Controls - York Predator MagnaDRY DR090 Series Installation Manual

264276-XIM-B-1208

ELECTRIC HEATING SEQUENCE OF OPERATIONS

The following sequence describes the operation of the elec-
tric heat section.
Two-stage heating:
a. Upon a call for first stage heat by the thermostat, the
heater relay (RA) 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 (RB) will be energized.
After completing the specified fan on delay for heat-
ing, 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 and a flash code is initi-
ated (See Table 34).

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 28. It resets automatically. The limit switch
operates when a high temperature condition, caused by inad-
equate supply air flow occurs, thus shutting down the heater
and energizing the blower.
TABLE 28: ELECTRIC HEAT LIMIT SETTING
UNIT (TONS) VOLTAGE
DR090 (7.5) 380/415
42
HEATER LIMIT SWITCH
kW OPENS °F
9 150
18 150
24 150
34 150

FLASH CODES

The UCB will initiate a flash code associated with errors
within the system. Refer to UNIT CONTROL BOARD FLASH
CODES Table 34.

RESET

Remove the call for heating by lowering the thermostat set-
ting lower than the conditioned space temperature.This
resets any flash codes.

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 29 for the required electric
heat anticipator setting.
TABLE 29: ELECTRIC HEAT ANTICIPATOR
SETPOINTS
SETTING, AMPS
W1
0.13

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 ignitor 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.
W2
0.1
Johnson Controls Unitary Products