Reznor HRPD, Installation, Operation And Maintenance Manual

24

RP-HRPD-IOM (07-22) 132210-B

CONTROLS—CONTINUED

Optional Two-Stage Control (Makeup Air Application)—Continued

• Option AG3 or AG15: 

Comparable to the two-stage heating units . Instead of control from a two-stage room 

thermostat, the discharge air temperature is monitored and the two-stage gas valve is controlled by a two-stage 

ductstat . When the discharge air temperature drops to the setpoint, low fire is energized . If low fire cannot satisfy the 

ductstat setting, high fire is energized . Model HRPD includes two furnace sections, and each section is equipped 

with a two-stage gas valve . Set the ductstat as indicated in 

Table 17

 .

• Option AG4 or AG17 (model HRPD only):  

Each furnace in the package is equipped with a single-stage gas 

valve . The single-stage gas valves are staged by a two-stage ductstat . The furnaces are staged in sequence . This 

concept will achieve two-stage control . Set the ductstat as indicated in 

Table 17

 .

Table 17.  Recommended Settings for Two-Stage Makeup Air Control

Option

Model

No. of 

Furnaces

Ductstat Setting

Temperature Selector Setting

First

Second

Staging Sequence

Setpoint

Differential

Stage Adder 

Offset

AG3

RP

1

70°F

—

66°F high stage

→

70°F low stage

→

74°F shutdown

—

—

—

HRPD

2

70°F

64°F

60°F high stage (both furnaces)

→

64°F low stage (furnace 2)

→

68°F shutdown (furnace 2)

→

70°F low stage (furnace 1)

→

74°F shutdown (furnace 1)

AG4

HRPD

2

70°F

—

66°F full rate (both furnaces)

→

70°F shutdown (furnace 1)

→

74°F shutdown (furnace 2)

AG15

*

RP

1

—

74°F

8°F

4°F

HRPD

**

2

—

74°F

14°F

10°F, 6°F, 4°F

AG17

*

HRPD

2

—

74°F

8°F

4°F

*

Adjust the setpoint and the differential of the temperature selector (Johnson #A350) . Adjust the offset potentiometer on each of the stage 

adder modules (Johnson #S350) . The settings listed provide the same sequence of staging as shown for option AG3 (for option AG15) or 

AG4 (for option AG17) . Follow the manufacturer’s instructions provided . 

IMPORTANT:

 Set the temperature selector and each stage adder 

module to HEAT . Follow the wiring diagram to obtain proper sequencing . 

Operation:

 The differential setting and offset degrees allow the 

controls to adapt to any adjustment in temperature selection (50–130°F) .

**

Model HRPD with option AG15 uses three stage adder modules .

Figure 14.  Ductstat Options

•

Depending on the option selection, the factory-installed sensor is either field-connected by capillary tubing to the 

unit-mounted ductstat (see 

Figure 14

, DETAIL A), which is factory-set at 70°F, or electrically-connected to a remote 

field-installed electronic temperature selector (see 

Figure 14

, DETAIL B) .

Ductstat Bulb 

Typical Duct Furnace 

Front (Discharge) View

DETAIL A: OPTIONS AG3 AND AG4

(A) Remote 

Temperature Selector 

(B) Stage-Adder 

Module

(A)

(B)

DETAIL B: OPTIONS AG15 AND AG17