NXQS-5 J30-10228-001 Quick-Start Installation Guide Tools Required • Combustion Analyzer • Phillips Screw Driver • Size 50-200: 2.5mm Allen Wrench • Wire Jumper • Size 300-400: Flat Head Screw Driver ! WARNING MUST BE FOLLOWED STEP BY STEP OR PROBLEMS WILL OCCUR 260 North Elm Street, Westfield, MA 01085 413-564-5540 www.sterlinghvac.
STEP 1 Remove control box cover and power venter access panel. Control Box Cover Power Venter Access Panel Burner Access Panel STEP 2 Turn power and gas on.
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 STEP 5 Jumper R to W1 to call for heat. Set Run % Potentiometer to 100%.
STEP 7 STEP 8 Adjust high fire on gas valve or trim valve based on Table 1. Set Run % Potentiometer to 33%. Note: Allow the unit to run for 2 minutes to ensure the unit to reaches 33% fire. Size 50-200: Gas Valve Run % Potentiometer High Fire Adjustment Size 300-400: Trim Valve High Fire Adjustment Table 1 High Fire Gas Valve Adjustment: Unit Size (MBH) CO2 Meter Reading Natural Propane Gas Gas 50 & 150 <7.4% <8.7% <7% <6.7% 50 & 150 >7.9% >9.3% >7.9% >7.6% Clockwise 100 & 200 <7.
STEP 9 Adjust low fire 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 50-200 <4.2% <5.3% <12% <12% 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.
STEP 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% fire (usually design outdoor air temperature used in sizing the unit).
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 fire.
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 firing rate set by the Run % Potentiometer. If the single stage thermostat is connected to the W2 terminal the unit will run at 100% fire. Dip Switch Settings: #1-5 – OFF Run % Potentiometer 260 North Elm Street, Westfield, MA 01085 413-564-5540 www.sterlinghvac.
