What does A9-02 mean?
Whenever working on any Daikin VRV system, there is always a possibility of generating an A9-02 error code. This code indicates that an indoor fan coil is experiencing refrigerant bleed-by. In this instance liquid refrigerant is passing through the indoor unit and returning back to the compressor, which can lead to potential damage if not addressed.
Why is an A9-02 error code bad for a system?
Why is liquid bad for a compressor? There are multiple reasons why liquid is bad for a compressor. Here are some reasons
- Liquid refrigerant is bad for a scroll compressor mainly because scroll compressors are designed to compress vapor not liquid. When liquid enters the compressor, it can cause several issues
- Liquid Slugging: A scroll compressor orbiting motion between two scroll plates needs to be precise. Liquid refrigerant cannot be compressed if it enters the compression chamber It creates extremely high pressure instantly. This can break scrolls, damage bearings, or even snap internal components.
- Oil dilution ( Mechanical seized): Liquid refrigerant will mix with and carry away compressor oil which will reduce lubrication inside the compressor. This will tend to increase wear, overheating, and eventual failure
How do you detect if an indoor EEV is bleeding by?
To determine if an indoor unit EEV is bleeding by, you need to verify whether refrigerant is flowing through the fan coil when the EEV should be closed.
Under normal operation:
- In Fan Mode, the EEV should be 100% closed.
- In Cooling Mode, when the unit is thermally off, the EEV should be 100% closed.
If refrigerant continues to flow through the fan coil while the EEV is commanded closed, the valve may be bleeding by.
The procedure below uses Service Checker data to verify proper EEV operation.
- If you have an ITM that has BMS controlling the fan coils disconnect them as you don’t want them to be interfering with your bleed by test
- Turn off auto changeover on the ITM. The system should only operate in cooling mode and fan mode. Do not allow any units to switch into heating mode.
- Connect your Service Checker to the system and confirm it is updated with the latest software version.
- Go to the main outdoor unit if there is more than one module that makes up for a system and activate mode 2-06 ( Forced Thermostat Operation)
- Depending on the amount of fan coils connected to your system, put 50% of them in fan mode and put the other 50% in cooling mode.
- Wait 20 minutes as this will allow compressor RPS to increase allowing the refringent to flow throughout the system.
- After the 20 minutes have passed look closely at the ones that are in cooling, verifying EEVs are responding and opening and allowing refrigerant to flow through each individual fan coil. In cooling mode fan coils will maintain 9 degrees of subcooling.
- Then look at the ones that are in fan mode. Your EEVs pluses should at 0, liquid, gas and suction thermistors should be +/- within 3 degrees of each other. Anything more you need to verify thermistors with actual pipe temperature clamps.
- Then you switch operations, meaning the ones that were in fan mode you will now put them in cooling, the ones that were in cooling you will put them in fan mode. Then wait 20 minutes again.
- If the liquid pipe temperature decreases after running in FAN mode for 20 minutes, the EEV is bleeding by.
Picture below shows a fan coil in fan mode. Look close to lines 163 through 165. This shows that this EEV is good and not bleeding by.
