14
System Operating Pressures
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Low suction pressure.
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Faulty evaporator fan motor. Repair or replace.
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Shortage of refrigerant. Test for leaks. Add refrigerant.
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Restricted liquid line. Replace restricted part.
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Dirty air filter. Inspect filter; clean or replace as needed.
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Dirty indoor coil. Inspect coil and clean, if needed.
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Not enough air across indoor coil. Check blower speed. Check duct static pressure and
filter.
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Dirty outdoor coil (heating only). Inspect coil and clean, if needed.
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Wrong type of expansion valve. Replace valve.
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Expansion valve restricted. Remove restriction or replace valve.
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Undersized expansion valve. Replace valve.
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Inoperative expansion valve. Check valve operation. Replace if needed.
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Faulty defrost control (heating only). Test control.
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Faulty defrost thermostat (heating only). Test defrost thermostat.
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Low head pressure.
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Shortage of refrigerant. Test for leaks. Add refrigerant.
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Restricted liquid line. Replace restricted part.
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Too much air across indoor coil (heating only). Reduce blower speed.
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Broken valves. Test compressor efficiency. Replace if needed.
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Inefficient compressor. Test compressor efficiency.
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Wrong type of expansion valve. Replace valve.
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Expansion valve restricted. Remove restriction or replace valve.
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Faulty reversing valve (heating only). Replace valve or solenoid.
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Faulty defrost control (heating only). Test control.
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Faulty defrost thermostat (heating only). Test defrost thermostat.
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Flowrator not seating properly. Check flowrator and seat, or replace flowrator.
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High suction pressure.
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Too much air across indoor coil. Reduce blower speed.
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Overcharge of refrigerant. Recover part of charge.
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Broken valves. Test compressor efficiency. Replace if needed.
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Inefficient compressor. Test compressor efficiency.
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Expansion valve bulb loose. Tighten bulb bracket.
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Faulty reversing valve (heating only). Replace valve or solenoid.
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Faulty defrost thermostat (heating only). Test defrost thermostat.
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Flowrator not seating properly. Check flowrator and seat, or replace flowrator.
Problem
No Cooling/Heating
Cause/Test Method and/or Solution