Gas Valve; Safety Controls; Limit Switch (Ls); Auxiliary Limit Switch (Als) - York Predator MagnaDRY DR120 Installation Manual

GAS VALVE

The UCB and ICB continuously monitor the GV.
If the ICB senses voltage at the GV when not requested, the
ICB will energize the draft motor. The ICB will not operate the
furnace until voltage is no longer sensed at the GV. The draft
motor is stopped when voltage is not sensed at the GV.
Any time the UCB senses voltage at the GV without a call for
heat for a continuous five-minute period, the UCB will lock-on
the indoor blower and a flash code is initiated (Table 41).
When voltage is no longer sensed at the GV, the UCB will de-
energize the indoor blower following the elapse of the fan off
delay for heating.
If voltage has been sensed at the GV for at least 15 seconds
during the fan on delay for heating and GV voltage or "W1" is
lost, the indoor blower is forced on for the length of the fan off
delay for heating.
During a call for heat, if the UCB does not sense voltage at
the GV for a continuous five-minute period the UCB will initi-
ate a flash code (Table 41). The indoor blower motor will not
be locked-on while there is no GV voltage.

SAFETY CONTROLS

The UCB monitors the temperature limit switch of gas heat
units.
The control circuit includes the following safety controls:

LIMIT SWITCH (LS)

This control is located inside the gas heat compartment and
is set to open at the temperature indicated in the Gas Heat
Limit Control Settings Table 37. 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.

AUXILIARY LIMIT SWITCH (ALS)

This control is located inside the supply air compartment and
is set to open at the temperature indicated in the Gas Heat
Limit Control Settings Table 37. It resets manually. 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.
The auxiliary limit switch is wired in series with the limit
switch. As such, the UCB cannot distinguish the auxiliary limit
and the gas heat limit switch operation except the auxiliary is
manual reset. Consequently, the control will respond in the
same manner as outlined above under "Limit Switch".
Johnson Controls Unitary Products
TABLE 37: GAS HEAT LIMIT CONTROL SETTINGS
# of HX Tubes
4
6
8
*.
Rollout = 300°F, Auxiliary Limit = 200°F.
The ICB monitors the Pressure and Rollout switches of gas
heat units.
The control circuit includes the following safety controls:

PRESSURE SWITCH (PS)

Once the draft motor has reached full speed and closes the
pressure switch during a normal ignition sequence, if the
pressure sw opens for 2 seconds, the GV will be de-ener-
gized, the ignition cycle is aborted, and the ICB flashes the
appropriate code. See Table 43 Ignition Control Flash Codes.
The draft motor is energized until the pressure switch closes
or "W1" is lost.

ROLLOUT SWITCH (ROS)

The rollout switch is wired in series with the pressure switch.
As such, the ICB cannot distinguish the rollout switch opera-
tion from that of the pressure switch.
Consequently, the control will only respond in the same man-
ner as outlined above under "Pressure Switch". An open roll-
out will inhibit the gas valve from actuating.

INTERNAL MICROPROCESSOR FAILURE

If the ICB detects an internal failure, it will cease all outputs,
ignore inputs, and display the proper flash code for control
replacement. The ICB remains in this condition until replaced.

FLASH CODES

The UCB will initiate a flash code associated with errors
within the system. Refer to UNIT CONTROL BOARD FLASH
CODES Table 41.

RESETS

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

GAS 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 38 for the required gas
heat anticipator setting.
127878-YIM-C-1208
Main Limit Setting
215°F
195°F
160°F
57
*