York ZT078-102 Installation Manual

Also see for ZT SERIES: Technical guide

6021980-UIM-A-112068 Johnson Controls Ducted SystemsCalculating the cubic feet of gas consumed per hour1. To find the BTU input, multiply the number of cubic feet ofgas consumed per hour by the BTU content of the gas inyour particular locality.Note: The BTU content of gas varies widely from area toarea, contact your gas company for this information.By actual measurement, it takes 46 seconds for the handon a 1 cubic foot dial to make a revolution with a 80,000BTU/h furnace running.2. To determine rotations per minute, divide 60 by 46 = 1.30.3. To calculate rotations per hour, multiply 1.30  60 = 78.4. Multiply 78  1 (0.5 if using a 1/2 cubic foot dial) = 78.5. Multiply 78  (the BTU rating of the gas). For this example,assume the gas has a BTU rating of 1050 BTU/ft. 3.The result of 81,900 BTU/h is within 5% of the 80,000 BTU/hrating of the furnace.Adjusting the manifold gas pressureThis gas furnace has two heat stages. The gas valve has twoadjustment screws located under a plastic protective cover. Thesecond stage (100% input) adjustment screw is adjacent to theHI marking on the valve. The first stage (60% input) adjustmentscrew is located adjacent to the LO marking on the valve (seeFigure 32).Adjust the second stage (100% input) pressure first, then adjustfirst stage (60% input) pressure.1. Turn off electrical power to the unit.2. Using the outlet pressure port on the gas valve, connect amanometer to monitor the manifold pressure.3. Remove the plastic cap that covers the HI and LO pressureadjustment screws.4. Turn on electrical power to the unit.5. Set the thermostat to call for second stage heat and startthe furnace.6. If necessary, use a screwdriver to turn the second stageadjustment screw clockwise to increase manifold pressureor counterclockwise to decrease manifold pressure.Note: Do not to over-fire the unit on second stage.7. After you check the high manifold pressure, adjust thethermostat to call for first stage heat.8. If necessary, use a screwdriver to turn the first stageadjustment screw clockwise to increase manifold pressureor counterclockwise to decrease manifold pressure.Note: Do not to under-fire the unit on first stage.9. After you check the pressure, replace the plastic capcovering the HI and LO pressure adjustment screws.Note: When using natural gas, the manifold pressure forsecond stage (100% input) is 3.5 IWG ± 0.3. Themanifold pressure for first stage (60% input) whenusing natural gas is 1.5 IWG ± 0.3.Adjusting the temperature riseThe temperature rise is the difference of temperature betweenthe return air and the heated air from the furnace. Thetemperature rise must lie within the range shown on the CSArating plate and the data in Table 13.1. After about 20 minutes of operation, determine the furnacetemperature rise. Take readings of both the return air andthe heated air in the ducts (about 6 feet from the furnace)where they are not affected by radiant heat.Table 29: Gas rate cubic feet per hourSeconds forOne Rev.Size of Test Dial1/2 cu. ft. 1 cu. ft.10 180 36012 150 30014 129 25716 113 22518 100 20020 90 18022 82 16424 75 15026 69 13828 64 12930 60 12032 56 11334 53 10636 50 10038 47 9540 45 9042 43 8644 41 8246 39 7848 37 7550 36 7252 35 6954 34 6756 32 6458 31 6260 30 60 Table 30: Gas heat stagesUnit No. of burnertubes1st stage input(100% BTU/h)2nd stage input(60% BTU/h)078, 090, 102,120, 1504 120,000 72,0006 180,000 108,0008 240,000 144,000Table 31: Gas heat limit control settings11. Roll-out = 300°F, Auxiliary limit = 200°FUnit Main limit setting °FSize Option078 N12 165N18 165090 N12 165N18 165102 N12 215N18 195120 N18 195N24 160150 N18 195N24 160