AIR CONDITIONING SYSTEM OVERVIEW / TROUBLESHOOTING TIPS
There are 4 basic descriptors of moisture contamination.
Contaminated Oil = Contaminated oil is determined by looking at its color.
Clear/yellow oil – new or used oil.
Light gray oil – Common in the first few hours of use. Light green/yellow oil – oil contains leak detection additive.
Silver/grey oil – indicates the presence of large metal particles in the oil.
Black oil – small particles are present in the oil. Brown oil (carbonized oil) – air conditioning system overheated due to capacitor failure, condenser clogged or airflow obstruction, defective pressure switch, or missing oil/refrigerant.
Orange oil (this only applies to Sanden oil) – oil contaminated by moisture.
Rust = Moisture over a long period of time
Rust can form on exposed internal steel compressor components.
Clogged valve = A clogged valve is a valve that has been permanently deformed due to fluid deceleration.
Copper Plating = Copper plating usually occurs when there is a high moisture content in the air conditioning system.
TROUBLESHOOTING TIPS
Undercharging – not enough gas in the system
Medium to high compressor discharge temperature.
This is because the liquid coming into the compressor is hot.
One of the functions of the suction gas is to cool the compressor. If the gas enters hotter than normal, it will also be hotter than normal when exiting.
High absorption superheating
The high overheating is due to the lack of liquid of the expansion device due to undercharging. When there is no liquid left in the expansion device, it will pass both liquid and vapor and will not be able to control excessive heat. Because there is not enough refrigerant in the system, all refrigerants reaching the evaporator will evaporate at an early stage and continue to absorb heat through the evaporator, resulting in high overheating.
Low capacitor supercooling
Subcooling is the key factor for detecting the correct refrigerant charge. As the refrigerant charge increases, supercooling increases. If there is no subcooling, there will be liquid and gas refrigerant at the inlet of the expansion device.
Low suction pressure
The suction pressure will be less due to the demand required by the compressor. The compressor will act as a vacuum pulling gas from the evaporator causing the low suction pressure.
Overcharging – too much gas in the system
High compressor discharge temperature
High discharge temperature is caused by increased discharge pressure.
High discharge pressure
The supercooled liquid will rise back up in the condenser, reducing the amount of surface area for the gas to cool. This will cause higher pressure.
High capacitor supercooling
This will cause the liquid to reach high supercooling temperatures due to the back-up liquid at the bottom of the condenser.
Normal extreme heat
The TXV will control overheating. There may be a slight difference during the first boot, but it will correct itself and control the excess heat.
Cannot be condensed – liquid in system
High compressor discharge temperature
High discharge temperature is caused by increased discharge pressure.
High discharge pressure
The supercooled liquid will rise back up in the condenser, reducing the amount of surface area for the gas to cool. This will cause higher pressure.
High capacitor supercooling
This will cause the liquid to reach high supercooling temperatures due to the back-up liquid at the bottom of the condenser.
Normal extreme heat
The TXV will control overheating. There may be a slight difference during the first boot, but it will correct itself and control the excess heat.
Restricted expansion device – clogging in TXV
Low suction pressure
The suction pressure will be less due to the refrigerant demand required by the compressor. The compressor will act as a vacuum pulling gas from the evaporator causing the low suction pressure. If the TXV is off, the pressure drop will be greater and thus the evaporation pressure will be lower due to the higher pressure drop.
High extreme heat
The temperature of the refrigerant remains constant during evaporation. When all the refrigerants have evaporated, the temperature begins to rise as a result of the heat exchange, thus increasing the excess heat.
High discharge temperatures
Discharge temperatures will be higher due to high excess heat.
Dirty or restricted airflow over the condenser – not enough heat transfer
High compressor discharge pressure
The discharge pressure will be higher due to the ideal gas law: P.V = n.r.T. If the gas temperature increases due to the restricted airflow and the volume remains the same, the pressure will increase.
High compressor discharge temperature
As the pressure increases, the temperature will increase, this is due to the higher compression ratio.
Dirty or restricted airflow over the evaporator – not enough heat transfer
Low compressor discharge pressure
Restricted airflow over the evaporator reduces the heat load to the evaporator and less energy is left to evaporate the refrigerant. The expansion valve must provide the correct temperature extremes. This means that the refrigerant must evaporate and overheat at the evaporator outlet. If the airflow is less, it means less refrigerant can evaporate.
r and so the expansion valve will close to prevent refrigerant from reaching the evaporator. If the TXV is off, the pressure drop will be greater and thus the evaporation pressure will be lower. If less refrigerant enters the expansion valve, the condenser pressure decreases due to the lack of refrigerant reaching the condenser.
Low excess heat
In an air conditioning system with a calibrated orifice, the excess heat will be lower due to less heat transfer through the evaporator. There is no excess heat when there is no heat load.
cold compressor crankcase
Since there is no heat transfer, the suction cooler will still be cold. This causes the crankcase to become cold.
Clutch does not engage – Compressor does not turn on
There is no voltage in the coil
Relay switch broken
Coil thermal fuse active
short circuit diode
Poor electrical connection at the compressor terminal