
| Table 40— Heating Service Analysis | |
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PROBLEM | CAUSE | REMEDY |
Burners Will Not | Misaligned spark electrodes. | Check flame ignition and sensor electrode positioning. Adjust as needed. |
Ignite. |
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No gas at main burners. | Check gas line for air purge as necessary. After purging gas line of air, allow gas | |
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| to dissipate for at least 5 minutes before attempting to relight unit. |
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| Check gas valve. |
| Water in gas line. | Drain water and install drip leg to trap water. |
| No power to furnace. | Check power supply, fuses, wiring, and circuit breaker. |
| No 24 v power supply to control circuit. | Check transformer. Transformers with internal overcurrent protection require a |
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| sary. |
| Miswired or loose connections. | Check all wiring and wirenut connections. |
| Replace thermostat. | |
| Broken thermostat wires. | Run continuity check. Replace wires, if necessary. |
Inadequate Heating. | Dirty air filter. | Clean or replace filter as necessary. |
| Gas input to unit too low. | Check gas pressure at manifold. Clock gas meter for input. If too low, increase |
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| manifold pressure or replace with correct orifices. |
| Unit undersized for application. | Replace with proper unit or add additional unit. |
| Restricted airflow. | Clean filter, replace filter, or remove any restrictions. |
| Blower speed too low. | Use high speed tap, increase fan speed, or install optional blower, as suitable |
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| for individual units, Adjust pulley. |
| Limit switch cycles main burners. | Check rotation of blower, thermostat heat anticipator settings, and temperature |
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| rise of unit. Adjust as needed. |
| Too much outdoor air. | Adjust minimum position. |
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| Check economizer operation. |
Poor Flame | Incomplete combustion (lack of | Check all screws around flue outlets and burner compartment. Tighten as nec- |
Characteristics. | combustion air) results in: | essary. |
| Aldehyde odors, CO (carbon monoxide), | Cracked heat exchanger. |
| sooting flame, or floating flame. |
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| Overfired unit — reduce input, change orifices, or adjust gas line or manifold | |
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| pressure. |
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| Check vent for restriction. Clean as necessary. |
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| Check orifice to burner alignment. |
Burners Will Not | Unit is locked into Heating mode for a | Wait until mandatory |
Turn Off. | one minute minimum. | unit. |
Table
PROBLEM | CAUSE |
| REMEDY |
Subcooling Mode (Liquid Reheat) | No power to control transformer from | Check power source and | |
Will Not Energize. | wire connections are tight. | ||
| No power from control transformer to liquid line | 1. | Fuse open; check fuse. Ensure continuity of wiring. |
| solenoid valve. | 2. | |
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| not close. |
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| 3. Transformer bad; check transformer. | |
| Liquid line solenoid valve will not operate. | 1. | Solenoid coil defective; replace. |
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| 2. | Solenoid valve stuck open; replace. |
| Liquid line solenoid valve will not open. | Valve is stuck closed; replace valve. | |
Low System Capacity. | Low refrigerant charge or frosted evaporator coil. | 1. | Check charge amount. Charge per Fig. |
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| 2. | Evaporator coil frosted; check and replace |
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| sure switch if necessary. |
Loss of Compressor Superheat | Thermostatic expansion valve (TXV). | 1. | Check TXV bulb mounting, and secure tightly to suc- |
Conditions with Subcooling/Reheat |
| 2. | tion line. |
Dehumidification Coil Energized. |
| Replace TXV if stuck open or closed. |
Table
PROBLEM | CAUSE |
| REMEDY |
Reheat Mode Will Not Energize. | No power to control transformer from | Check power source and | |
| wire connections are tight. | ||
| No power from control transformer to hot gas | 1. | Fuse open; check fuse. Ensure continuity of wiring. |
| line solenoid valve | 2. | |
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| not close. |
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| 3. Transformer bad; check transformer. | |
| Hot gas line solenoid valve will not operate. | 1. | Solenoid coil defective; replace. |
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| 2. | Solenoid valve stuck closed; replace. |
| Low refrigerant charge or frosted evaporator coil. | 1. | Check charge amount. Charge per Fig. |
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| 2. | Evaporator coil frosted; check and replace |
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| sure switch if necessary. |
Loss of Compressor Superheat | Thermostatic expansion valve (TXV). | 1. | Check TXV bulb mounting, and secure tightly to suc- |
Conditions with Subcooling/Reheat |
| 2. | tion line. |
Dehumidification Coil Energized. |
| Replace TXV if stuck open or closed. | |
Excessive Superheat. | Liquid line solenoid valve will not operate. | Valve is stuck, replace valve. | |
| Hot gas line solenoid valve will not close. | Valve is stuck; replace valve. |
581B,C
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