Sterling NXQS-5 Installation Guide

Quick-Start

Installation Guide

NXQS-5

J30-102 28-001

Tools Required

• Combustion Analyzer

• Size 50-200: 2.5mm Allen Wrench

• Size 300-400: Flat Head Screw Driver

WARNING

!

MUST BE FOLLOWED STEP BY STEP OR PROBLEMS WILL OCCUR

• Phillips Screw Driver

• Wire Jumper

260 North Elm Street, Westeld, MA 01085
413-564-5540
www.sterlinghvac.com

STEP 1

Remove control box cover and power venter access panel.

Control Box Cover

Power Venter Access Panel

STEP 2

Turn power and gas on.

Note: Remember to turn gas valve on/o switch to the “On” position

Size 50-200: Gas Valve On/O Switch

Burner Access Panel

Size 300-400: Gas Valve On/O Switch

2

STEP 3

Set gas control mode dip switches #1-5 to zero.

Note: Dip switches #6-8 should not need to be changed since they are set by the factory for the unit size. See “Dip Switch
#6-8” table in OPERATION section of the unit installation manual for additional information. If applicable remove the 2-10
VDC wires from control board.

Switches 1-5 for Gas Control Mode

STEP 4

Jumper R to W1 to call for heat.

STEP 6

Place combustion analyzer in ue pipe.

STEP 5

Set Run % Potentiometer to 100%.

Note: Allow the unit to run for 2 minutes to ensure the unit
reaches 100% re.

Run % Potentiometer

3

STEP 7

Adjust high re on gas valve or trim valve based on Table 1.

Size 50-200: Gas Valve

High Fire Adjustment

STEP 8

Set Run % Potentiometer to 33%.

Note: Allow the unit to run for 2 minutes to ensure the unit
to reaches 33% re.

Run % Potentiometer

Size 300-400: Trim Valve

High Fire Adjustment

Table 1

High Fire Gas Valve Adjustment:

CO2 Meter Reading O2 Meter Reading Action Required

Unit Size

(MBH)

50 & 150 <7.4% <8.7% <7% <6.7%

50 & 150 >7.9% >9.3% >7.9% >7.6% Clockwise

100 & 200 <7.5% <8.9% <6.9% <6.5%

100 & 200 >8.0% >9.3% >7.7% >7.6% Clockwise

300 <7.5% <8.6% <6.9% <6.5%

300 >8.0% >9.0% >7.7% >7.3% Clockwise

400 <7.5% <8.6% <6.9% <6.5%

400 >8.0% >9.3% >7.7% >7.6% Clockwise

Natural

Gas

Propane

Gas

Natural

Gas

Propane

Gas

Gas Valve

Adjustment

Counter

Clockwise

Counter

Clockwise

Counter

Clockwise

Counter

Clockwise

4

STEP 9

Adjust low re on gas valve based on Table 2.

Size 50-200: Gas Valve Size 300-400: Gas Valve

Low Fire Adjustment Gas Valve Adjustment

Table 2

Low Fire Gas Valve Adjustment:

CO2 Meter Reading O2 Meter Reading Action Required

Unit Size (MBH) Natural Gas Propane Gas Natural Gas Propane Gas Gas Valve Adjustment

50-200 <4.2% <5.3% <12% <12% Clockwise

50-200 >5.0% >5.8% >13.3% >12.7%

300 <4.0% <5.0% <12.3% <12.5%

300 >4.5% >5.4% >13.6% >13.1% Clockwise

400 <4.2% <5.3% <12% <12%

400 >5.0% >5.8% >13.3% >12.7% Clockwise

Counter

Clockwise

Counter

Clockwise

Counter

Clockwise

STEP 10

Remove R to W1 jumper. Turn thermostat to lowest
setting and conrm unit turns o.

5

ST EP 11

Select desired gas control and set thermostat to desired temperature.

Switches 1-5 for Gas Control Mode

Modulating with Outdoor Air Reset (Master) – This gas control should be used in regions with large temperature swings.
The unit will automatically vary the discharge air temperature based on the outside air temperature. Set the “Design T/
Space SP” potentiometer to outdoor air temperature where the unit should be at 100% re (usually design outdoor air
temperature used in sizing the unit).
Note: If ordered with Outdoor Air Reset, unit will come with an Outdoor Air Sensor for eld installation. The unit can be
eld converted to Outdoor Air Reset by ordering the Outdoor Air Sensor, part number 11J11R09966-001.

Dip Switch Settings: #1 & 3 – ON; #2, 4 & 5 – OFF

Modulating with Outdoor Air Reset (Network) – This gas control modulates the unit the same as Outdoor Air Reset
(Master). However, it does not require a separate outdoor air sensor. It allows the master unit to share the outdoor air
temperature with all networked units. Set the “Design T/Space SP” potentiometer to outdoor air temperature where the
unit should be at 100% re (usually design outdoor air temperature used in sizing the unit).
Note: One master unit is required per networked group; when networked together, the Master and Member units need
to be set to the same Modbus address.

Dip Switch Settings: #1 & 4 – ON; #2, 3 & 5 – OFF

Design T/Space SP Potentiometer

6

Indoor Air Reset – This gas control attempts to learn your building’s heating needs and run at the bare minimum to keep
the space temperature within the allowed range. The unit will vary the discharge air temperature so the unit is running at
lowest output possible without short cycling.
Note: A W2 call will act as a room override and force the unit to high re.

Dip Switch Settings: #2 – ON; #1, 3-5 – OFF

Room Sensing – This gas control allows the unit to vary the discharge air temperature to more closely match the needs
of the space for precise temperature control. Set “Design T/Space SP” potentiometer to desired room temperature.
Note: If ordered with Room Sensing, unit will come with a Room Sensor for eld installation. The unit can be eld
converted to Room Sensing by ordering the Room Sensor, part number 11J11R09974-001.

Dip Switch Settings: #1 & 2 – ON; #3, 4, & 5 – OFF

Design T/Space SP Potentiometer

2-10 VDC/4-20 mA Input – This gas control allows the unit to vary the discharge air temperature based on a signal from
the building automation system.
Note: Units can also be controlled via a Modbus signal. See Operation Section of unit installation manual for additional details.

Dip Switch Settings: 2-10 VDC Input: #1-5 – OFF; 4-20 mA Input: #5 – ON; #1-4 – OFF

Two Stage – While designed for modulating gas control, the Nexus unit can be used with two stage gas control. A W1
signal will cause the unit to run at the ring rate set by the Run % Potentiometer. A W2 signal will cause the unit to run at
100% re.

Dip Switch Settings: #1-5 – OFF

Run % Potentiometer

7

Single Stage – While designed for modulating gas control, the Nexus unit can be used with single stage gas control.
By connecting the single stage thermostat to the W1 terminal, the unit will run at the ring rate set by the Run %
Potentiometer. If the single stage thermostat is connected to the W2 terminal the unit will run at 100% re.

Dip Switch Settings: #1-5 – OFF

Run % Potentiometer

260 North Elm Street, Westeld, MA 01085
413-564-5540
www.sterlinghvac.com