REFRIGERATION TROUBLESHOOTING! | F-GAS

 

SOME COMMON SOURCES OF OPERATING DIFICULTIES

ΕΓΓΡΑΦΕΙΤΕ ΣΤΟ ΚΑΝΑΛΙ ΜΑΣ ...

The analysis of operating troubles is difficult.

The ability to analyze them correctly can be acquired only through thought | knowledge and experience.

Although the causes of a number of operating difficulties are listed below, such a list can serve only as a guide. It cannot replace thought and experience.

 

 PRESS BELOW, TO WATCH A VIDEO:

1.     Shortage of Refrigerant

Shortage of refrigerant usually manifests itself by a warm liquid line. There should always be sufficient liquid in the receiver (when exists) to completely submerge the inlet of the liquid pipe line.

 

While superheat indicates how much refrigerant is in the evaporator (high superheat indicates not enough, low superheat indicates too much), subcooling gives an indication of how much refrigerant is in the condenser.

 

Subcooling on systems that use a thermostatic expansion valve (TXV) should be approximately 10°F to 18°F.

Higher subcooling indicates excess refrigerant backing up in the condenser.

On TXV systems with high superheat, be sure to check the subcooling as refrigerant is added.

 

If the superheat doesn't change, and the subcooling increases, the problem is with the metering device. In the case of a TXV, it's likely that the power head needs to be replaced.

 

2.     Expansion Valve obstructed

Sometimes the expansion valve may stick in a nearly closed position. Occasionally frozen moisture or dirt will also obstruct the flow of refrigerant liquid through the valve. In any event only a small trickle of refrigerant liquid may be flowing through the valve.

 

In such a case the compressor may short-cycle, starting and stopping at frequent intervals, because insufficient liquid is admitted to the coil.

 

3.     Expansion Valve completely closed

Occasionally an expansion valve may stick in the closed position or frozen moisture or dirt in the valve may prevent the flow of any liquid at all into the evaporator. In such a case, the compressor will pull the pressure in the coil down to the point where the low pressure control will stop the compressor.

 

The suction pressure will be low, but the cooling coil and suction line will be warm. If it happens, a small amount of leakage is taking place through the valve; the compressor may run for a very short time at infrequent intervals (short cycling).   

 

4.     Leaking power element on expansion valve

The power element of an expansion valve consists of the thermal bulb, connecting tubing and the bellows, which opens the valve. If the power element is leaking the valve will either maintain an almost closed position or may even close completely.

 

5.     Expansion Valve stuck in open position

If it happens there will be an excessive amount of sweating on the suction line due to an excessive amount of liquid being admitted to the low side of the system.

Occasionally the valve may open excessively because the contact between the thermal bulb and the suction pipe is not insulated.

In either case the bulb will be warmer than the cold suction vapor.

 

 

6.     Solenoid valve leaking

If it happens while in the closed position, the compressors will usually short-cycle.

The liquid line leaving the valve will feel cooler than the inlet side and in some cases there may be some sweat or frost at the outlet side.   

 

7.     Strainer clogged with dirt

Occasionally a strainer in the liquid line may be clogged with dirt.

When this occurs the liquid line on the outlet side of the strainer will feel cooler than the liquid line entering it.

Occasionally if it is badly clogged some sweat or frost may make its appearance at the outlet.

 

 

8.     Valve on liquid receiver partially closed

If the main liquid line valve, located at the liquid receiver is partially closed, the liquid line will feel cooler than the liquid in the receiver.  

Other symptoms will be too, such as compressor short-cycling.

 

9.     Obstruction in liquid line

When there is an obstruction in the liquid line, the portion of the pipe after the obstruction will feel cooler than the pipe ahead of it.

In extreme cases there may even be some sweating or frost after the obstruction.

The compressors will usually short-cycle.

The cooling coil and the suction pipe will be warm.

 

10.  High pressure drop through cooling coil

If there

is a high pressure drop, the expansion valve will reduce the flow.

In such a case part of the coil and the suction line will be warm.

An equalizer connection installed between the expansion valve and the point on the suction line at which the temp bulb is located will allow the valve to admit enough liquid to cool the entire coil surface.

In addition because of the smaller pressure difference available, a larger orifice may be needed for the expansion valve.     

 

 

11.  Orifice in expansion valve too small

If the pressure drop available for the expansion valve has been incorrectly computed, the orifice in the expansion valve may be too small.

In such a case insufficient liquid will be admitted to the coil and a part of the cooling coil and the suction line will be warm.

The suction pressure will also be low.

 

12.  Shortage of condenser water

When there is a shortage of condenser water due to the main water valve being partially closed, an automatic valve being stuck in any almost closed position or improper adjusted, or a lack of pressure in the water mains, the head pressure in the condenser will rise and the condenser will feel warm.

The liquid line will also feel warm.

The condenser pressure may even rise to the point where either the high-pressure switch or the thermal overload elements in the motor starter will stop the condenser.

 

If the high-pressure switch stops the motor and the high pressure switch is not a manual reset type, the compressor will short-cycle.

During the intervals when the compressor is off, the small amount of water available will reduce the head pressure to the point where the pressure switch, if it is automatic reset type, can start the motor again.

However, if the motor overloads sufficiently for the overload elements in the motor starter to stop the compressor, there will be no short cycling, but the compressor will start again after the thermal overload elements are reset.       

 

 

13.  Expansion valve improperly adjusted

If the expansion valve is adjusted to pass too much liquid to the coil, all of the symptoms will be as described in #5.

If the expansion valve is adjusted to pass too little liquid to the coil, all of the symptoms will be as described in #2.

Occasionally a valve may be out of adjustment only slightly, in which case none of symptoms described above will be apparent.

 

14.  Too much oil in crankcase

If there is too much oil in the crankcase, there may be some pounding in the compressor due to slugs of oil being thrown about.

In recip. compressors this may result in valve damage.

 

15.  Air in the Condenser

If air or other noncondensable gases are present in the condenser, the head pressure may rise to a point considerably above the pressure corresponding to the temperature at which the vapor is condensing.

In extreme cases the pressure may rise to a point where either the high pressure switch or the thermal overload elements in the motor starter may stop the compressor.

 

In order to purge a fluorinated hydrocarbon condenser, all of the refrigerant should be condensed and pumped over into a receiver and/or condenser.

 

 

16.  Insufficient water or air over evaporative condenser

If there is a shortage of water or air over an evaporative condenser all of the symptoms described in #12 will make their appearance.

 

It may be due to a dirty suction screen in the condenser | dirty spray nozzles | leakage at pump packing glands | a float on a make-up water being stuck in a closed position | pump motor trouble | some obstruction in the pipeline.

 

Insufficient air may be due to dirty filters, too high a resistance in the ductwork, or some obstruction such as damper being closed,     

 

 

17.  Coil too large for cooling load.

In such a case the expansion valve may admit so little liquid to the coil that the compressors will short-cycle.

In such a case increasing the differential spread on the low-pressure control, may sometimes be of help.

 

18.  Too much Refrigerant in the System

An overcharge of refrigerant in the system will cause nigh head pressures.

Liquid will back up into the condenser and decrease the area of surface available for condensing purposes.

As a result the head pressure will rise.

 

 

19.  Scale trap at suction of compressor clogged

When the scale trap at the suction of the compressor becomes clogged, the suction pressure may fall to a point where the duplex pressure switch will stop the compressor.

However the suction pressure gauge may still show normal suction pressure, failing completely to show the low pressure that is opening the switch and stopping the compressor.

This will happen if the suction pressure gauge is connected into the suction pipeline ahead of the scale trap.

When the scale trap is clogged, the suction pressure will be low only beyond the scale trap, not ahead of it.

However, if the suction gauge is connected into the crankcase, it will indicate the actual low pressure existing there.

Suction gauges should always be connected to the crankcases through the same tubing that connects the low-pressure element of the duplex switch.    

 

20.  Thermal overload elements in motor: starter too small

If the thermal overload elements in the motor starter are too small, the starter will open and stop the compressor almost immediately after it is started.

This is because the heater elements cannot carry the normal running current of the motor.

 

 

21.   Low-pressure control set too high

If the low-pressure control is set at too high a point, the compressor will short-cycle continuously.  

 

22.  High-pressure control set too low

If the high-pressure control is set at too low a point, the compressor will cycle off (!) on the high pressure control.  

 

 

23.  Valves in compressor broken

If valves are broken, there will be considerable noise in the compressor.

The suction pressure will be high, while the discharge pressure will be low.

In multi-cylinder reciprocating compressors, the temperature of the cylinder heads will differ if the valves in one of them are broken or defective.   

 

24.  Suction valves leaking

If the compressor suction valves are leaking, the suction connection and perhaps a small part of the suction line will be warm, while the balance of the suction line is cool.

This is due to a small amount of hot gas leaking back from the compressor chamber through the suction valve and into the suction line.

 

 

25.  Compressor bearings frozen

If the compressor bearings are frozen because insufficient oil is supplied to them, they will bind the shaft and prevent the compressor from running.  

 

26.  Moving parts of compressor sticking

Occasionally the moving parts of the compressor will stick due to corrosion or accumulated dirt and prevent the compressor