York DHG180 Installation Instruction

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York DHG180 Installation Instruction Manual pdf 20 page image

035-17233-000-C-070220 Unitary Products3. A Low Pressure Switch/Loss Of Charge to protectagainst loss of refrigerant charge. (Opens at 7 psig + 3and resets at 22 psig + 5)If either one of the above safety controls opens, that individ-ual refrigerant system will be locked out. The other refrigerantsystem will continue in operation unless it too is effected bythe same fault. The lock out of either system can be reset byopening the 24V circuit either at the room thermostat or at theunit disconnect.HEATING SYSTEMThe following sequence describes the operation of the gasheat section.CONTINUOUS BLOWERWith the room thermostat switch set to ON, the supply airblower will operate continuously. The normally closed contactK5-1 provides 24 volt power to the M3 contactor. The M3-1, 2& 3 power contacts close and the blower motor operates.INTERMITTENT BLOWERWith the room thermostat system switch set to the AUTO orHEAT position and the fan switch set to AUTO, the supply airblower will operate after the room thermostat calls for heatand the time delay relay closes.The TH1 closes, the heat relay RW1 is energized. The RW1-1 power contact closes energizing the line voltage draftmotor. The RW1-2 contact is also closed. As the speed of thedraft motor reaches approximately 2500 RPM, the centrifugalswitch contact located on the end of the draft motor shaftcloses to power the first stage ignition module IC1.Ignition module IC1 will immediately start the first stage igni-tor sparking and will open the redundant valve located insidethe first stage main gas valve GV1 to allow a flow of gas toonly the first stage carryover tube. See Figure 14. Only afterthe pilot flame has been ignited and the presence of pilotflame detected at the IC1 by a signal sent back through theflame sensor is sparking terminated and the first stage maingas valve opened.Gas flows into each of the main burners and is ignited fromthe carryover tube flame.If IC1 fails to detect a pilot flame, it will continue to try for amaximum of 85 seconds to ignite the pilot tube. If the pilotflame is not detected, then IC1 will lock out first stage furnaceoperation until 24V power is removed from the module eitherat the unit or by resetting the room thermostat.At the same time power was supplied to the RW1, a parallelcircuit activates ETD which closes the ETD contact afterapproximately 35 seconds and energizes K5 which closesK5-2 and starts the blower by energizing M3.When TH2 closes, heat relay RW2 is energized. The RW2-1contact is closed energizing the second stage ignition moduleIC2. IC2 will immediately start the second stage ignitor spark-ing and will open the redundant valve located inside the sec-ond stage main gas valve GV2 to allow a flow of gas to thesecond stage carryover tube. See Figure 11. Only after thepilot flame has been ignited and the presence of pilot flamedetected at IC2 by a signal sent back through the flame sen-sor is sparking terminated and the main gas valve opened.Gas flows into each of the second stage main burners and isignited from the carryover tube flame.If IC2 fails to detect a pilot flame, it will continue to try for amaximum of 85 seconds to ignite the pilot tube. If the pilotflame is not detected, then IC2 will lock out first stage furnaceoperation until 24V power is removed from the module eitherat the unit or by resetting the room thermostat. Note that thesecond stage furnace can operate even if first stage haslocked out.When the heating cycle is complete, TH2 opens de-energiz-ing the RW2 then TH1 opens de-energizing RW1 and ETD,thus closing all gas valves. The blower motor will continue torun (approximately 45 seconds after the furnace is shutdown) until ETD opens, de-energizing the K5 relay and M3contactor.SAFETY CONTROLSThe control circuit includes the following safety controls:1. Limit Control (LS). This control is located inside the heatexchanger compartment and is set to open at the tem-perature indicated in Table 16. It resets automatically.The limit switch operates when a high temperature con-dition, caused by inadequate supply air flow occurs, thusshutting down the ignition control and closing the maingas valves and energizing the blower.2. Centrifugal Switch (CS). If the draft motor should fail, thecentrifugal switch attached to the shaft of the motor pre-vents the ignition controls and gas valves from beingenergized.FIGURE 14 : GAS VALVE PIPINGGASVALVEGAS MAINMAIN VALVETO MAINBURNERREDUNDANTVALVETO PILOT BURNER