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AIR CONDITION SYSTEM ON

BOARD SHIPSA GUIDE FOR SOLVING COMMON PROBLEMS

PREPARED BY: Sharad Pradhan

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INTRODUCTION

It is understood that the reader is familiar with the basic theory andoperation of A/C and refrigeration systems.

This presentation covers only how to solve problems associated withthe systems.

Reader is advised to read the makers instruction manual before

attempting to solve any problems.

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A/C SYSTEMS- WHAT COOMON PROBLEMS DO I ENCOUNTER?

MOST COMMON: COOLING EFFECT IS INSUFFICIENT.

Evaporator gets blocked by ice.

Compressor runs hot.

Compressor has a history of breaking down frequently.

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CHECKS ON A FAULTY PLANT

DOMESTIC A/C SYSTEM:

Check the Condenser liquid level in gauge glass is atleast 2 Cm from bottom, while the plant is running.

The sight glass fitted on liquid line after the condenser

is full, without any bubbles. The color of the centre dotin the glass should correspond to dry (green).

Check that the compressor oil level is normal.

Confirm the compressor suction pressure is atminimum 5.0 Kg/Cm2 This is an important check.

On Air-Handling unit (Evaporator) Check that the airsuction filters are clean.

Air outlet is maximum 16 Deg.C.

Check various flaps & dampers on cold air lines areopen or closed as required.

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WHAT DO THE CHECKS ON PAGE-3 TELL ME?

Condenser: Low liquid level shows under-chargedsystem. The system may have refrigerant leaks.

Liquid flow sight glass: Bubbles show that the systemis under-charged or condenser needs cleaning. If the

centre dot color matches wet, the system hasmoisture.

Compressor oil level low: Oil Charge low or the Oilseparator fitted on the compressor delivery may bemalfunctioning. The oil separator may not be present in

all installations. Suction pressure lower than 5.0 Kg/Cm2: shows either

or all of the following: a) refrigerant charge low b)Expansion valve has been wrongly adjusted c) Liquidflow in the system is low due to throttled liquid linevalve d) Evaporator blocked with ice formation.

Air handling unit checks are self-explanatory.

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CORRECTING FAULTS NOTICED DURING CHECKS

Charge the refrigerant in the system. Ensure that theevaporator sight glass level is at about 2 Cm from thebottom of gauge when the system is running.

After charging sufficient gas, the liquid sight glass will befull. If still bubbles are visible, then lower the cooling

water temperature or increase its flow. Charge the compressor Sump with recommended Lube oil

till the level in the sight glass is about full. Adjust the compressor suction pressure is done by

correctly adjusting the expansion valve & superheat. Thisis factory set and should never be adjusted by theships staff. Best is to replace valve cages with original

spare factory set pieces. Compare the spare valve cagesnumber with originals to ensure correct capacity asdesigned.

The method of carrying out superheat adjustment isexplained on slide- 8

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MOST COMMON OBSERVATIONS

Almost all of the faults encountered in theA/C system can be divided into 2 maincategories as follows:-

1. Refrigerant charge low. Will cause a)Low cooling capacity b) Ice formation onevaporator c) Compressor suctionpressure low.

2. Maladjustment of components. Willcause a) any or all symptoms as perabove b) will cause total break-down ofcompressor.

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ADJUSTING THE EXPANSION VALVE

Note that the adjustment should only be carried out as a lastresort.

Onboard vessels, you will find these 3 makes of expansion valvesa) Saginomiya b) Alco C) Danfoss

Read the instructions as given by these makers and adjustexpansion valve cage/ Orifice to get a superheat of 4Deg.C.

On Alco valve, you will have to turn the screw, causing valvespring tension to change. On the other 2 brands, spring tension ischanged in a different way.

The best suggestion is to order new valve cages and fit in place.Note that you will have to order these by the refrigerationcapacity.

Attach the expansion valve sensor bulb in a correct position as

per the maker- this is very important. Always wait for few minuits for the system to stabilize after initial

adjustmant before carrying out more adjustments.

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MORE ON A/C SYSTEM

During my career, I have noticed the following wrongadjustments done by Ships staff.

1. Trying to increase the A/C cooling capacity: Lookslike this is a desperate attempt (unfortunately) to getrid of some ships staff complaint of feeling too hot!.

Please read the specifications of the A/C plant. Thecooling capacity of the plant is normally sufficient tolower the inside accommodation temperature bymaximum 6 Deg.C only. Believe it or not this isusually true with both A/Cs running.

2. Adjusting the Expansion valves. For all practicalpurposes, the factory set / commissioningadjustments must be retained forever. So calledadjustments of the ships staff will eventually lead tocomplete break-down of the A/C plant.

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MORE ON A/C SYSTEM

3. Changing adjustments of LP cut-out. Thisis the most common fault to be found.Too low setting of the LP cut-out pressure

setting will cause: Icing of theevaporator.

4. Changing of Automatic un-loaderPressure settings. This has to be usually

done after lowering the LP setting. Thismay cause total break-down of thecompressor.

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MORE ON A/C SYSTEM

The expansion valve thermal sensing bulb must becorrectly attached to the return pipe as shown.

EXPANSION VALVE

THERMAL SENSING

BULB. LOCATION IS

3 OCLOCK

GAS RETURN PIPE

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MORE ON A/C SYSTEM

Suction pressure:

5.0 to 5.6 normal