Table 19. Pressure Switch Settings
Unit
Size
Negative Pressure (IN WC)
Label
Color
Startup Cold Equilibrium Hot Setpoint OFF Setpoint ON
055 1.90 1.60 0.60 0.75
Purple085 1.80 1.30 0.60 0.75
110 1.15 1.15 0.60 0.75
130
3.50 3.00 2.40 2.65 White
180 3.20 2.50 2.30 2.45 Blue
260 3.50 3.10 2.40 2.65
White
310 3.30 2.80 2.40 2.65
CONTROLS—CONTINUED
Pressure Switch—Continued
38
UEZ-IOM (07-23) 1034347-I
High Temperature Limit Control
⚠ WARNING ⚠
The automatic-reset high temperature limit control will continue to shut down the heater until the
cause is corrected. Never bypass this control as hazardous conditions could result.
All units are equipped with a temperature-activated, automatic-reset high temperature limit control (see Figure 27
for location). The control is factory-set and is non-adjustable. If the setpoint is reached, the control interrupts the
electric supply to the combination gas valve. This safety device provides protection in the case of motor failure or
lack of airflow due to a restriction at the inlet or outlet.
Vent Temperature Limit Switch
⚠ WARNING ⚠
If the manual vent temperature limit switch activates, identify and correct the cause before resetting
the switch. Never bypass the vent temperature switch as hazardous conditions could result.
All units are equipped with a temperature-activated, manual-reset switch to limit the temperature of vent gases to
below 145°F. The switch is attached to the side of the combustion air venter housing (see Figure 27 for location). If
the setpoint is reached, the switch interrupts the electric supply to the combination gas valve. If the switch is activated,
identify and correct the cause before resetting the switch.
Interlock Door Switch
All units are equipped with an interlock door switch (see Figure 27 for location) that prevents the heater from operating
when the service door panel is open. The service panel is equipped with a pliable gasket that fully seals the door to
provide added protection to prevent building air from entering the combustion zone of the heater.
Fan Motor
The fan motor is equipped with automatic-reset thermal overload protection. If the motor does not run, the cause
may be due to improper current. Ensure that the correct voltage is available at the motor.
Circuit Board (DSI Control Module)
The heater’s ignition system is controlled by a circuit board (Direct-Spark Integrated (DSI) control module, see Figure
26) that monitors the safety devices and controls the operation of the fan and venter motors and the combination
gas valve between heat cycles. To view the Seven-Segment Display (SSD), the door panel requires removal. In
addition, there is a status LED on the bottom of the heater. Its status indications are off (heater is not powered or
control board fault), steady on (heater is on with no faults), or flashing (heater is on with fault(s)). Additional status
indications appear on the display at the bottom of the control module (labeled as DSP1, see Figure 26). The display’s
codes are listed and described in the Unit Troubleshooting Using DSI Control Module section.
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