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Maritime Forum

TOPIC: Refrigeration System

Refrigeration System 28 Mar 2017 05:08 #4768

  • PMA-3777
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With reference to refrigeration system:

(a) Rapidly drop crankcase oil in vee block compressor.

(b) Steady fall off effect on short running.

(c) Excess icing up at compressor suction.

(d) Short cycling.
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Refrigeration System 06 Apr 2017 08:39 #4776

(A) Drop in suction pressure will lead to excessive carryover of crankcase oil or there could be leakage from the crankcase shaft seal.

(C) Causes of the excess icing in the Compressor suction are following:
1. Over charging of refrigerant.
2. Faulty Thermostatic expansion valve.
3. Blocked evaporator due to icing or under-size evaporator.
4. Faulty back-pressure valves of the Evaporators.

(D) Short cycling occurs in the compressor when a mechanical failure is causing the run times to terminate prematurely and since set point has not been achieved, it restarts shortly afterward, thus requiring more compressor ‘ON’ time to compensate. Short cycling is a symptom of a potentially wide range of causes.

Dirty condenser/automatic high pressure reset: A dirty condenser can severely limit your system’s ability to reject heat for regulating temperatures and pressures needed for cooling which can lead to compressor tripping on high head pressure. If the condenser has automatic high pressure reset it can result in short run cycles.

Pressure or temperature control differential is too small: When the pressure controller’s low pressure differential is set too tight, it can cause the compressor to short cycle. This can be observed during normal cooling when the low pressure setting is reached and the compressor cycles off until the pressure in the evaporator rises above the high side of the low pressure setting. This results in longer times to achieve set point and greater energy use.

Lack of operation time delay: While it’s certainly important to have a minimum and maximum run time in place for proper system performance, it’s equally important to have a minimum OFF time in the form of an operation time delay. This is arguably the most common cause of a short cycle. By having an effective time delay, you can potentially prevent other causes from infiltrating your system. For example, a proper time delay can keep the system from running due to discharged air still circulating in the system immediately after its operation. Another: it can allow the pressure controller to reset itself naturally while not calling for cooling as opposed to firing another cycle based on high pressure triggers due to compromised condensers.
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