REFRIGERATION -5- FAULT FINDING

DETECTING AND CORRECTING PROBLEMS

A number of symptoms indicate faulty operation of refrigeration and air-conditioning plants. The table below list some possible causes  and corrective measures and includes recommended test procedures that may be used to isolate the problems.

Trouble	Possible Cause	Corrective Measure
High condensing pressure.	Inlet water warm.	Purge air from condenser
	Air on non-condensable gas in  system.	Increase quantity of condensing water.
	Insufficient water flowing through condenser.	Increase quantity of water.
	Condenser tubes clogged or scaled.	Clean condenser water tubes.
	Too much liquid in receiver, condenser tubes submerged in liquid refrigerant.	Draw off liquid into service cylinder.
Low condensing pressure.	Too much water flowing through condenser.	Reduce quantity of water.
	Water too cold.	Reduce quantity of water.
	Liquid refrigerant flooding back from evaporator.	Change expansion valve adjustment, examine fastening of thermal bulb.
	Leaky discharge valve.	Remove head, examine valves. Replace any found defective.
Frosting or sweating of a liquid line.	Refrigerant line restriction.	Check for partially closed stop valve, or stuck solenoid valve.
	System low on refrigerant.	Check for leaks, add refrigerant.
High suction pressure. Compressor crankcase sweating	Overfeeding of expansion valve.	Regulate expansion valve, check bulb attachment.
	Leaky suction valve.	Remove head, examine valve and replace if worn.
Low suction pressure.	Restricted liquid line and expansion valve or suction screens.	Rump down, remove, examine and clean screens,
	Insufficient refrigerant in system.	Check for refrigerant storage.
	Too much oil circulating in system.	Check for too much oil in circulation. Remove oil.
	Improper adjustment of expansion valves	Adjust valve to give more flow.
	Expansion valve power element dead or weak	Replace expansion valve power element.
Compressor short cycles on low- pressure control.	Low refrigerant charge.	Locate and repair leaks. Charge refrigerant.
	Thermal expansion valve not feeding properly. Dirty strainers. Moisture frozen in orifice or orifice plugged with dirt. Power element dead or weak	Adjust, repair or replace thermal expansion valve. Clean strainers. Remove moisture or dirt (use system dehydrator). Replace power element.
	Water flow through evaporators restricted or stopped. Evaporator coils plugged, dirty, or clogged with frost.	Remove restriction. Check water flow. Clean coils or tubes.
	Defective low-pressure control switch.	Repair or replace low-pressure control switch.
Compressor runs continuously.	Shortage of refrigerant.	Repair leak and recharge system.
	Leaking discharge valves.	Replace discharge valves.
Compressor short cycles on high- pressure control switch.	Insufficient water flowing through condenser, clogged condenser.	Determine if water has been turned off. Check for scaled or fouled condenser.
	Defective high-pressure control switch.	Repair or replace high-pressure control switch.
Compressor will not run.	Seized compressor.	Repair or replace compressor.
	Cut-in point of low-pressure control switch too high.	Set L. P. control switch to cut-in at correct pressure.
	High-pressure control switch does not cut-in. 1 .Defective switch. 2. Electric power cut off. 3. Service or disconnect switch open. 4. Fuses blown. 5. Over-load relays tripped. 6. Low voltage. 7. Electrical motor in trouble. 8. Trouble in starting switch or control circuit. 9. Compressor motor stopped by oil pressure differential switch.	Check discharge pressure and reset P. H. control switch. 1. Repair or replace switch. 2. Check power supply. 3.Close switches. 4. Test fuses and renew if necessary. 5. Re-set relays and find cause of overload. 6. Check voltage (should be within 10 percent of nameplate rating). 7. Repair or replace motor. 8. Close switch manually to test power supply. If OK, check control circuit including temperature and pressure controls. 9. Check oil level in crankcase. Check oil pump pressure.
Decreased capacity of the compressor.	High vapor superheat.	Adjust or replace expansion valve.
Sudden loss of oil from crankcase.	Liquid refrigerant slugging back to compressor crank case.	Adjust or replace expansion valve.
Capacity reduction system falls to unload cylinders.	Hand operating stem of capacity control valve not turned to automatic position.	Set hand operating stem to automatic position.
Compressor continues to  operate at full or partial load.	Pressure regulating valve not opening.	Adjust or repair pressure regulating valve.
Capacity reduction system fails to load cylinders.	Broken or leaking oil tube between pump and power element.	Repair leak.
Low discharge pressure with high suction pressure.	Discharge relief valve leaking back to the suction side.	Replace relief valve.
Compressor continues to  operate unloaded.	Pressure regulating valve not closing.	Adjust or repair pressure regulating valve.
Compressor oil brownish in color	Copper plating caused by moisture in the system.	Change filter drier, or dehydrator.
Compressor oil gray or metallic.	Compressor bearing wear or piston scoring.	Replace or overhaul compressor.
Compressor oil black	Carbonization resulting from air in the system.	Remove air from system.