ICP 9MPT Service Manual

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ICP 9MPT Service Manual Manual pdf 22 page image

Two- Stage Multi Position FurnaceService Manual20440 08 2002 0223. HONEYWELL SV9541Q SYSTEM OPERATION & DIAGNOSTICSThe following is the normal operating sequence for the 2--stage control system.Cooling (Y) Request:24 VAC signals applied to Y & G terminals of EFT (electronic fan timer) control.· Cool motor speed energized after 5 second Cool Fan On Delay time.Y & G signals removed from EFT.· Cool motor speed de--energized after 60 second Cool Fan OffDelay time.Cooling (Y) and dehumidification (Y2) requests:· 24 VAC signals applied to Y, Y2 & G terminals of EFT (electronic fan timer) control.· Same operation as the cooling (Y) request, except the cooling speed is reduced 20% to compensate for high humidityconditions during cooling operation. The cooling speed returns to the normal setting after the Y2 signal is removed.Circulating Fan (G) Request:24 VAC signals applied to G terminals of EFT control.· Low motor speed energized without delay.G signal removed from EFT.· Low motor speed de--energized without delay.NOTE1) Furnaces with DC blower motors run a low circulating fan speed in response to G request.NOTE2) Furnaces with PSC blower motors de--energize the Low Heat fan speed during the heat exchanger warm--upperiod on a call for Heating that occurs during a G request.NOTE3) Heating or Cooling requests received during a Fan request cause the fan speed to change to the appropriate heator cool speed after the selected Fan On Delay time expires. The fan returns to circulating speed after the selected Fan OffDelay time expires following loss of the Heating or Cooling request.Heating (W1) Request (single stage thermostat operation, 4th DIP switch must be in off position) (see furnacewiring diagram):24 VAC signals applied to W1 terminal of EFT control.· Inducer motor turns on at high speed.· The high fire solenoid energizes.· Following a 3 second prepurge delay, the pilot valve opens and the ignitor begins to warm up.· After the pilot lights, the main burners energize and light (burners now at high fire rate).· Timed from the opening of the main gas valve, the control will delay the selected Heat Fan On Delay time beforeswitching the inducer to low speed, de--energizing the high fire solenoid and the fan switches to Low Heat speed.· Timed from initial application of the Heating request, if the W1 request is still present after the selected Low Fire Delaytime expires (12 minutes), the inducer switches to high speed, the high fire solenoid energizes and the fan switches toHigh Heat speed.W1 signal removed from EFT.· The gas valve de--energizes and the main burners go out.· The inducer runs at its present speed for a 5 second postpurge period.· The fan switches to (or stays at) Low Heat speed.· Timed from the gas valve de--energizing, the Low Heat fan speed de--energizes after the selected Heat FanDelay time expires.NOTE4) If a new Heating request arrives while the control iswaiting in the Heat Fan Off Delay time, the fan speed switches toHigh Heat until the Heat Fan Off Delay expires or the Heat FanOn Delay expires for the new Heating request.Heating Request (two stage thermostat operation, 4th DIP switch must be in on position) (see furnace wiringdiagram):24 VAC signals applied to W1 terminal of EFT control.· Same response as single stage thermostat operation described above except the control will not go to high fire, HighHeat fan speed unless a W2 signal is applied.