Garland MCO-GD-10E, MCO-GD-10M, MCO-GS-10E, MCO-GS-10M

and answering conditions in each box encountered, until a problem and/or the repair is explained. After any

maintenance or repair, the trouble shooting sequence should be repeated until the trouble shooting procedure ends

with a normal system operation.

S86 CHECKOUT AND TROUBLE SHOOTING

START

NOTE: Before troubleshooting, familiarize yourself

with the startup and checkout procedure.

TURN GAS SUPPLY OFF.

TURN THERMOSTAT

(CONTROLLER) TO CALL

FOR HEAT

POWER TO MODULE (24v

NOMINAL)

Check line voltage power, low voltage transformer, limit controlle r, thermostat

(controller) and wiring.

SPARK ACROSS

IGNITOR/SENSOR GAP

Pull ignition lead and

check spark at module.

Spark okay?

• On models with vent damper plug, make sure vent

damper had not been installed, then remove.

Replace vent damper if necessary.

• On other models, replace module.

• Check ignition cable, ground wiring, ceramic insulator and gap, and correct.

• Check boot of the ignition cable for signs of melting or buckling. Take protective

action to shield cable and boot from excessive temperature.

TURN GAS SUPPLY ON

PILOT BURNER LIGHTS?

• Check that all manual gas valves are open, supply tubing and pressure are good,

and pilot burner orifice is not blocked.

• Check electrical connections between module and pilot operator on gas control.

• Check for 24 Vac across PV-MV\PV terminals on module. If voltage is okay,

replace gas control; if not, replace module.

SPARK STOPS WHEN

PILOT IS LIT?

NOTE: If S8600B,H; S8610B, H goes into lockout, reset system. For S8600M,

wait 6 minutes nominal for retry or reset system.

• Check continuity of ignition cable to ground wire.

• Clean flame rod.

• Check electrical connection between flame rod and module.

• Check for cracked ceramic flame rod insulator.

• Check that pilot flame covers rod and is steady and blue.

• Adjust pilot flame.

• If problem persists, replace module.

MAIN BURNER

LIGHTS?

• Check for 24 Vac across MV-MV\PV terminals. If no voltage, replace module.

• Check electrical connections between module and gas control. If okay, replace

gas control or gas control operator.

SYSTEM RUNS UNTIL

CALL FOR HEAT

LOSS?

NOTE: If S8600B,H; S8610B, H goes into lockout, reset system. For S8600M,

wait 6 minutes nominal for retry or reset system.

• Check continuity of ignition cable and ground wire.

NOTE: If ground is poor or erratic, shutdowns may occur occasionally even

though operation is normal at the time of checkout.

• Check that pilot flame covers flame rod and is steady and blue.

• If checks are okay, replace module.

CALL FOR HEAT ENDS

SYSTEM SHUTS OFF?

• Check for proper thermostat (controller) operation.

• Remove MV lead at module; if valve closes, recheck temperature controller and

wiring; if not, replace gas control.

TROUBLESHOOTING

ENDS

Repeat procedure until troublefree operation is obtained.

YES