CHAPTER 11 MECHANICAL TROUBLESHOOTING PART 1 PROBLEM ANALYSIS

CHAPTER 11 MECHANICAL TROUBLESHOOTING PART 1

PROBLEM ANALYSIS • TYPICAL TROUBLESHOOTING BEGINS WITH A UNIT THAT WAS INSTALLED, CHECKED OUT & HAS BEEN WORKING SATISFACTORILY FOR SOME TIME

PROBLEM ANALYSIS • TWO BASIC AREAS OF MECHANICAL PROBLEMS: • AIR-SYSTEM PROBLEMS • REFRIGERATION SYSTEM PROBLEMS

AIR-SYSTEM PROBLEMS • REDUCTION OF AIR FLOW: • DIRTY FILTERS • DIRTY COILS • BLOWER MOTOR OPERATING AT BELOW NORMAL SPEED • UNUSUAL RESTRICTIONS IN DUCT SYSTEM

AIR FILTERS • DISPOSEABLE TYPE SHOULD BE CHANGED AT LEAST 2 TIMES A YEAR • DUSTY AREAS, EVERY 30 DAYS • IN COMMERCIAL AREAS, PROPER PM SCHEDULING MUST BE WORKED OUT

BLOWER MOTOR & DRIVE • FAN BLADE CLEAN • DIRECT DRIVE: • MOTOR BEARINGS LUBRICATED • BELT PROPERY ADJUSTED

UNUSUAL RESTRICTIONS IN DUCT SYSTEM • FURNITURE OR CARPET OVER REGISTERS OR GRILLES • SHUTTING OFF AIR TO UNUSED ROOMS • COLLAPSE OF DUCT • SOMETHING SUCKED INTO RETURN MIGRATING TO COIL OR FAN

REFRIGERATION PROBLEMS • TWO MAJOR CATAGORIES OF REF. SYSTEM PROBLEMS: • REFRIGERANT QUANTITY: • UNDERCHARGE • OVERCHARGE • REFRIGERANT RATE OF FLOW: • RESTRICTION • DIRTY DRIER • PLUGGED METERING DEVICE • TXV BULB LOST CHARGE

REFRIGERATION SYSTEM INDICATORS • SH = EOT – ECT • SC = CCT - LLT • TD = CCT - AA • E DELTA T = S/A – R/A

INSUFFICIENT LOAD CONDITION • CAUSES LOW DISCHARGE PRESSURE & SUCTION PRESSURE • MAY CAUSE FREEZE UP • CAUSES HIGH E DELTA T & LOW SH • MAY CAUSE HIGH SC

EXCESSIVE CONDITIONS • WILL CAUSE HIGH HEAD & SUCTION PRESSURES • WILL CAUSE HIGH SH & TD • WILL CAUSE LOW SC

LOW AA CONDITIONS • CAUSES LOW HEAD & SUCTION PRESSURES • CAUSES LOW TD & HIGH SC • MAY STARVE METERING DEVICE DUE TO REFRIGERANT STAYING IN CONDENSER

HIGH AA CONDITIONS • HIGHER TD & HEAD PRESSURES • SUCTION PRESSURE MAY BE HIGH • LOWER SC • AMP DRAW WILL ALSO BE HIGH • MAY BE CAUSED BY RECIRCULATION

REFRIGERANT UNDERCHARGE • LOW HEAD & SUCTION PRESSURES • HIGH SH • LOW TD • LOW SC • LOW E DELTA T

REFRIGERANT OVERCHARGE • HIGH HEAD & SUCTION PRESSURES • LOW SH • HIGH SC • NORMAL – LOW E DELTA T • REDUCES CAPACITY • HIGH AMP DRAW • MAY SWEAT COMPRESSOR SHELL

LIQUID LINE RESTRICTION OR PLUGGED CAP TUBE/ORIFICE • SUCTION PRESSURE LOW • SH HIGH • SC HIGH • DISCHARGE PRESSURE LOW OR NEAR NORMAL • LOW E DELTA T

SUCTION LINE RESTRICTION • LOW SUCTION PRESSURE • EXTREMELY HIGH SUPERHEAT • LOW DISCHARGE PRESSURE • LOW AMP DRAW ON THE COMPRESSOR

HOT GAS LINE RESTRICTION • SUCTION PRESSURE HIGH • SH HIGH • SC HIGH • HIGH AMP DRAW!!!

INEFFICIENT COMPRESSOR • SUCTION PRESSURE HIGH • DISCHARGE PRESSURE LOW • LOW AMP DRAW • SC LOW • COMPRESSOR WILL NOT PUMP DOWN BELOW 15” VAC