Troubleshooting Vapor-Compression (Mechanical)
Refrigeration & Air-Conditioning Systems

From Air Conditioning & Refrigeration Toolbox Manual, David J. Tenenbaum, 2nd edition, Jan. 2006, ISBN 0-7689-2235-6, Thomson Peterson's, $14.99 Sample pages
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Start at primary problem:
1: Unit fails to start
3: Unit runs, inadequate cooling
2: Unit runs erratically 4: Compressor loses oil
2: Unit runs erratically





Compressor short-cycles

Control circuit makes and breaks

Faulty control

Use meters to isolate problem control

Repair or replace


Low-pressure control short-cycles

Leaks, plugged filter-drier in liquid line, low air flow across evaporator, solenoid not closing, control set too close

Use gauge manifold to isolate problem

Repair leaks, adjust or replace components as necessary



Low evaporator load, low air flow

Examine load situation, check for dirty filter-drier plugging evaporator air flow, check for broken fan belt or motor problems

Repair problem: shut off unused evaporators on multi-evaporator system


High-pressure control short-cycles

Air-cooled condenser plugged with debris or fan inoperative

Compare condenser inlet to outlet air temperature; inspect condenser fan and controls

Repair or replace as indicated



Water-cooled condenser not opening, cooling tower pump not working, strainer plugged, water side of condenser fouled or scaled

Compare inlet to        outlet water temperatures in condenser; inspect condenser pump, piping, controls, water valve; check for plugged strainers in piping (pull out plug at bottom of strainer and check that water runs out)

Repair or replace valve; clean or replace strainer



Pump motor faulty

Check relays and capacitor

Replace part or repair motor


Leaving condenser temperature too warm

Condenser pump not pumping enough water

Check holding coil of pump controller, vent condenser

Repair or replace if still needed



Non-condensables in system, or overcharge of refrigerant

Check for non-condensables, then check charge level

Bleed off non-condensables or excess refrigerant

Compressor runs continuously

Room too cold or product temperature too cold

Thermostat not opening, contacts welded on low-pressure cutout (LPCO)

Check calibration of thermostat, check action of LPCO

Repair or replace as indicated