14
Table 14.1
Propeller and Blower Unit Heaters – PDP and BDP Models
Single-Stage, Standing Pilot, 100% Shut-Off – Utilizes a single-stage combination gas
control and thermocouple. Pilot needs to be manually lit initially and stays lit.
Single-Stage, Intermittent Pilot Ignition, 100% Shut-Off with Continuous Retry – Utilizes
a single-stage combination gas control and an ignition control (continuous retry). Pilot is
automatically lit on call for heat.
Two-Stage, Intermittent Pilot Ignition, 100% Shut-Off with Continuous Retry – Utilizes
a two-stage combination gas control (which fires at 50% or 100% of full rated input) and an
ignition control (continuous retry). Pilot is automatically lit only on call for heat. Available on
model sizes 50-400.
Mechanical Modulation with Automatic Pilot Ignition, 100% Shut-Off with Continuous
Retry – Utilizes a modulating combination gas control and an ignition control (continuous retry).
Pilot is automatically lit whenever there is power to the unit. Modulation range is between 50% and
100% fire; gas control shuts off below 50% fire. Available on blower models only.
11
12
13 ➀
14 ➀
81
82
91 ➀
92 ➀
30
31
32 ➀
33 ➀
85
86
93 ➀
94 ➀
63
64
87
88
59
60
89
90
115V
200/230V
460V
575V
115V
200/230V
460V
575V
115V
200/230V
460V
575V
115V
200/230V
460V
575V
115V
200/230V
115V
200/230V
115V
200/230V
115V
200/230V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25V
25v
natural
natural
natural
natural
propane
propane
propane
propane
natural
natural
natural
natural
propane
propane
propane
propane
natural
natural
propane
propane
natural
natural
propane
propane
Control System Description
Control
Code No.
Service
Voltage
Thermostat
Voltage
Type of
Gas
Two-Stage Gas Controls (intermittent pilot)
Utilizes a two-stage combination gas control, an ignition control,
and a two-stage low voltage thermostat. The unit fires at 50%
fire on low stage and 100% fire on high stage.
1. The thermostat calls for low stage heat.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed,
the differential pressure switch closes.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot.
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The main gas valve is opened and the main burner is lit to
50% fire.
6. The air mover starts after 30 to 90 seconds.
7. If the temperature at the thermostat continues to fall, the
thermostat will call for high stage heat.
8. The main gas valve is opened completely and the main
burner is lit to 100% full fire.
9. The unit continues to operate until the high stage of the
thermostat is satisfied, at which time the main valve closes
to 50% fire.
10. The air mover stops after 30 to 90 seconds.
Mechanical Modulating Gas Controls
Utilizes a mechanical modulating gas control and an ignition
control. The mechanical modulating gas control is designed
for use in constant blower applications. The discharge air
temperature is maintained by setting the control dial of the
modulating gas valve in one of ten positions. A hydrostatic
sensing bulb located in the discharge air stream controls
the gas flow between 50% through 100% full fire. When
the discharge air hydrostatic sensing bulb is satisfied, the
modulating valve closes completely, but the pilot remains lit.
This control cannot be used with a room override thermostat.
1. Power is supplied to the unit through either an exhaust fan
interlock contact or a start/stop switch.
2. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. The blower starts at this time.
3. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
4. The hydrostatic sensing bulb, integral to the mechanical
modulating gas valve, calls for heat. The power exhauster
relay is energized starting the power exhauster motor.
Once the motor has reached full speed, the differential
pressure switch closes. The main gas valve is opened and
the main burner is lit. The burner modulates between 50%
through 100% fire based on the call for heat.
5. The unit continues to operate until the hydrostatic sensing
bulb is satisfied, at which time the main valve closes 100%,
but the pilot remains lit.
6. The unit blower (and pilot) continues to operate until either
an exhaust fan interlock contact or a start/stop switch is
opened.
Dial Number
Lo 1 2 3 4 5 6 7 8 Hi
Discharge
Air Temp. 58 62 65 69 72 76 79 83 86 90
(°F)
START-UP PROCEDURE
➀ Factory wired 460/575 available on blower models. Field installed step down transformer may be used for 460/575 propeller applications.
