White Rodgers 21V51U-843 Wiring diagram
Contents
1. stage 3 W2 present with no W1 Second stage call for heat on thermostat circuit with no call for first stage Verify DIP switches are set for two stage thermostat and check thermostat first stage circuit Configured for a multi stage thermostat the Module will not initiate heating unless first stage call from thermostat is received 4 Y present with no G call Module will allow cooling to operate with only a Y signal from the thermostat but will also trigger this code Verify thermostat is energizing both Y and G on call for cool Check G terminal connections Rapid Low flame sense current Low flame sense current is often caused by carbon deposits on the flame sensor a poorly grounded furnace or a mis aligned flame sense probe Carbon deposits can be cleaned with emery cloth Check for improve furnace and module ground Verify sensor is located in or very near flame as specified by the appliance manufacturer 1 Standby or Call for Cool Normal operation Waiting for call from thermostat or receiving thermostat call for cool DIAGNOSTIC FEATURES The control continuously monitors its own operation and the operation of the system If a failure occurs the diagnostic in dicator LED DSI will flash a RED failure code If a failure is internal to the control the RED indicator will stay on continuously In this case the entire control should be replaced as the control is not field repairable If the LED is continuously OFF ther2. I COLOR DSI LED DIAGNOSTIC TABLE Green Amber Red LED Error Condition Comments Troubleshooting LED LED Flash Flash Flash 1 Flame sensed when no flame should be present Verify the gas valve is operating and shutting down properly Flame in burner assemble should extinguish promptly at the end of the cycle Check orifices and gas pressure 2 Pressure switch stuck closed inducer error Pressure switch stuck closed Check switch function verify inducer is turning off 3 1st stage pressure switch stuck open inducer Check pressure switch function and tubing Verify inducer is turning on the error pulling sufficient vacuum to engage switch 4 Open limit switch Verify continuity through rollout switch circuit 5 Open rollout open fuse detect Verify continuity through rollout switch circuit check fuse 6 1st stage pressure switch cycle lockout If the first stage pressure switch cycles 5 times open closed during one call for heat from the thermostat the control will lockout Check pressure switch for fluttering inconsistent closure or poor vacuum pressure 7 External lockout retries exceeded Failure to sense flame is often caused by carbon deposits on the flame sensor a disconnected or shorted flame sensor lead or a poorly grounded furnace Carbon deposits can be cleaned with emery cloth Verify sensor is not contacting the burner and is located in a good position to sense
3. INTEGRATED 21V51U 843 WIRING FURNACE CONTROLS White Rodgers AND CONFIGURATION The 50V51 843 has only one serviceable part an automotive type fuse which protects the low voltage transformer from dam age if the output is short circuited If the fuse has opened up remove whatever caused the short circuit and replace the fuse with only a 3 amp automotive type fuse If the fuse is not the cause of the control s problem replace the entire 50V51 843 control There are no other user serviceable parts Following installation or replacement follow appliance manu facturer s recommended installation or service instructions to insure proper operation 50V51 843 TYPICAL SYSTEM WIRING DIAGRAM HOT LINE 120 VAC NEUTRAL LINE 24 VAC CLASS II TRANSFORMER INDUCER HUMIDIFIER OPTIONAL ELECTRONIC AIR CLEANER OPTIONAL THERMOSTAT CONDENSING UNITS I HIGH LIMIT ROLLOUT 17 N C SWITCH N C SWITCH N O CIRC INTER CIRCULATOR FACE IGNITOR 1ST STAGE PRESSURE FLAME SENSOR mL FP PROBE 2ND AUX HIGH LIMIT N C LEGEND Low Voltage 24 VAC Line Voltage 120 VAC N C Normally closed switch N O Normally closed switch STAGE PRESSURE SWITCH N O www white rodgers com 181 a Ww x a lt 2 z I O wW a l Wu lt q 9 z lt S Wu 21V51U 843 OPERATION White Rodgers INTEGRATED FURNACE CONTROLS TR
4. e may be no power to the control or a failure within the control If the sensed failure is in the system external to the control the LED will flash RED in the sequence listed in the Diagnostic Table The LED will also indicate System Status as per the Amber and Green LED signatures listed in the Diagnostic Table The LED will flash one RED flash at power up CFM INDICATOR The LED DS2 CFM flashes when the blower motor is running The flashing indicates the motor CFM cubic feet per minute 182 air flow designated by the furnace manufacturer Consult the furnace manufacturer for flash code detail FAULT CODE RETRIEVAL To retrieve fault codes push and release the LAST ERROR button for more than 1 5 second and less than 5 seconds Control will indicate this period by solid GREEN for 1 5 secs to 5 secs The LED will flash up to five stored fault codes beginning with the most recent If there are no fault codes in memory the LED will flash two green flashes The control will flash the most recent error first and the oldest error last last in first out There shall be 2 seconds between codes Solid LED error codes will not be displayed These error codes may be different from furnace label or furnace manual www white rodgers com
5. flame Check sensor lead for shorting and verify furnace is grounded properly 8 External lockout ignition recycles exceeded Check items for exceeded retries listed above and verify valve is not where flame is established and then lost dropping out allowing flame to be established and then lost 9 Grounding or Reversed polarity Verify the control and furnace are properly grounded Check and reverse polarity primary if incorrect 10 Module gas valve contacts energized with no Verify valve is not receiving voltage from a short If a valve wiring is correct call for heat and condition persists replace module 11 Limit switch open possible blower failure Possible blower failure restricted air flow through appliance or duct work overheating limit Verify continuity through limit switch circuit and correct overheating cause 12 Module Ignitor contact failure Fault code indicates the module ignitor contacts are not functioning properly Replace module Solid Module internal fault condition Module contacts for gas valve not operating or processor fault Reset control if condition persists replace module 3 2nd stage Pressure Switch Stuck Open Inducer Check pressure switch function and tubing Verify inducer is turning on and double _ Error pulling sufficient vacuum to engage switch 1 Normal Operation with call for first stage heat Normal operation first stage 2 Normal Operation with call for second stage heat_ Normal operation first
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