Safety Controls; Limit Switch (Ls); Auxiliary Limit Switch (Als); Pressure Switch (Ps) - York DM090 Installation Manual

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 52).
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 ini-
tiate a flash code (Table 52). 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 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 44. 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.

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 46. 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".
TABLE 46: GAS HEAT LIMIT SETTINGS
Unit
Size Opt.
10
DM090
15
DM120 15
DM150 15
*.
Rollout = 300°F (148.9°C), Auxiliary Limit = 200°F
The ICB monitors the Pressure and Rollout switches of gas
heat units.
The control circuit includes the following safety controls:
44
*
Main Limit Setting
Natural Gas LPG
165°F (73.9°C) 175°F (79.4°C)
165°F (73.9°C) 185°F (85°C)
195°F (90.5°C) 195°F (90.5°C)
195°F (90.5°C) 195°F (90.5°C)
(93.3°C)

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 53 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 52.

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 47 for the required gas
heat anticipator setting.
TABLE 47: GAS HEAT ANTICIPATOR SETPOINTS
SETTING, AMPS
W1
0.65
FIGURE 28 - TYPICAL FLAME
127408-YIM-B-0606
W2
0.1
Unitary Products Group