Possible reasons Measures, recommendations
Safety cut-out
+ suction pressure too low
– faulty TX valve function
à check function and superheat setting
– insufficient refrigerant
à check system for leaks, charge to minimum level
– insufficient evaporator capacity
à clean, if iced-up cure the cause, check fan
– evaporator filled/coated with excessive oil
à reduce oil charge
– Suction filter blocked or throttling in suction
à cure cause, possibly change filter
shut-off valve, liquid or suction line
+ suction / condensing pressure too high
– insufficient condenser capacity
à clean, check fan
– too much refrigerant
à reduce to minimum level
– foreign gas
à purge
– discharge shut-off valve throttled à open fully
+ discharge gas / oil temperature too high (discharge gas: max. 120°C on outside of discharge line,
oil: max. 80°C outside on crankcase (paint removed))
– insufficient refrigerant
à check system for leaks, charge to minimum level
– by-pass between high and low pressure
à check / exchange relief valve, check plant
– inert gas à purge
+ defective / leaking working valves
– valve / gasket bridge broken
à repair, cure cause (valve breakage mainly caused by
liquid slugging due to excessive refrigerant, too much oil
or faulty TX valve regulation; with discharge valve breakage
danger of damage to connecting rod bearing)
– contamination (oil coke / foreign particles)
à clean / exchange, cure cause (oil coke mainly due to
excessive operating temperature or inert gas)
+ leaking cylinder head gasket à exchange (do not oil asbestos free gaskets!)
Compressor cuts out due to LP/HP pressure switch or discharge gas temperature protection
Insufficient capacity
+ suction pressure too low à see "safety cut-out"
+ insufficient pressure generation
– defective / leaking working valves
à see "safety cut-out"
– worn piston rings / cylinder liners
à exchange of connecting rods/pistons and liners
– leaking cylinder head gasket
à exchange (do not oil asbestos free gaskets!)
– by-pass between high and low pressure
à check / exchange internal relief valve, check plant
– capacity control sticking à repair / exchange
+ abnormal operating conditions
– too low / too high superheat
à see "safety cut-out"
– application limits exceeded
à see "safety cut-out"
– inert gas
à purge
– too much / too little refrigerant
à charge / reduce to minimum level
– too much oil
à reduce quantity of oil
Compressor provides too little refrigeration capacity
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