Problem with a Daikin Compressor - Please help!

[Brandon3131]

I posted this in another thread, but I think it belongs here. I'm posting from the US, and I hope you experienced guys in the UK can help us out with this problem.
We've got a Daikin VRV_II condenser that seems to be getting hot gas back to the compressor somehow. We've replaced the 4-way valve twice. The guy that replaced it the first time didn't use a heat sync and totally melted the plastic actuator inside. We've done a proper replacement on the 4-way valve but we have to run the unit on the standard compressor only. For some reason the inverter compressor is getting a tremendous amount of hot gas back in and it gets dangerously hot very very fast. I forgot to add in my last post that both compressors have been replaced. The inverter burned out first, then the standard. This job has been a nightmare for us.
I must add that the guys who did the original install were crap and the machine has never really worked right. Can anyone offer input for the cause of this?? PLEASE HELP. Cheers.

[Brian_UK]

Sounds like the reversing valve may be stuck again.

[regcooldude]

brandon, is it 407c ??

[cool#9]

Hi Brandon
I could help with the whole reference of your VRV 2.
If it's heat recovery model like REYQ "XX" M we had the same problems in France.
awaiting to your reply
rgds
cool#9

[Bullwinkle1]

There is a hot gas bypass valve on that unit that will open to increase the low side pressure during certain demands. If you have a service manual it will show you refrigerant flow in the manual and you can follow the flow to see if the valve is open for some reason. If it is open it is feeding hot gas to the low side. If this is a heat recovery system, 3 pipes off of the condenser then in full cooling, all indoor units calling for cooling, then there will be to 2 suction lines going to the indoor units. That is the suction and hot gas line off of the condensor will both be used as suction lines to feed the indoor coils. When 1 fan coil calls for heat then the hot gas line will start to feed hot gas inside to the branch selector box so that fan coil will recieve hot gas.

Go to Daikin's US website daikinac.com and you can download any service manual you need. Look at the refrigerant flows in the service manual and you will see where the bypass valve is located and you could do a touch test at the valve to see if it is flowing thru the valve. If it is then you have the valve powered up for some reason or possibly the valve has something in it blocking it and not allowing it to close.

If the install is as bad as you say then there could be some trash in the system. Did they use any leak lock on the flare joints in the system?Daikin does not want anything used on the flare joints.

Best thing you can do is familiarize yourself with the refrigerant flow of the system then you will be able to go thru the system and see where you have hot gas bleeding over to the low side.

[Brandon3131]

Thanks for the reply. It is an RXYQ96MTJU, 8-ton heat pump.

[Brandon3131]

Thanks for the reply - no, it is a R-410a system.

[desA]

Thanks for the reply. It is an RXYQ96MTJU, 8-ton heat pump.

You may want to refer to the following thread:
http://www.refrigeration-engineer.com/forums/showthread.php?p=157542#post157542

I wonder if your evaporator saturation temp (at low pressure) is running up beyond 13-15'C? If so, then order a few spare compressors - you may need them.

:)

[Brandon3131]

I believe a few evaporators are. We just discovered that the installer may have (I cannot imagine how...) piped the fan coils in reverse. I believe they piped the liquid line to the suction connection, and vice versa. If that were the case, what would the resulting pressures/ temperatures be on the low side of the system? Not many people I have spoken to have ever seen this happen, so people can only speculate. Thanks for your response. Cheers.

[kev99]

right....

your compressor bypass valve (dumping valve) is jammed open. possibly a piece of inline filter cage has broken away and caught under the seat.

i had one similar, but by the time i returned with the equipment to do it, it had moved into the system and was back to normal... BUT its still in there :eek:

[Brandon3131]

Thanks for the reply Kev99. That is a possibility as well. Thing is we have noticed that only 2 of the 5 fan coils (when operating alone) work beautifully (pressures are perfect/ temperatures are great...etc) BUT - as soon as we put any of the other 3 fan coils on, the low side pressure raises up by about 40 to 50 psi. To me, it points to the fan coils being piped backwards... What do you think? Cheers.