Head scratcher

[Dylan2980]

Good evening all. Just did a Emerson digital scroll compressor change out on a 16 ton Daikin after a burn out. Change out went well until vacuum pull down. Before vacuum a nitrogen charge and leak check was done and no leaks found. Vacuum pull down began to get erratic at about 700micron. Check all Schrader caps and valves, everything is tight and no apparent leaks. Figure maybe there was moisture in the system so continue to pull and finally after about four hours finally reach about 590 micron. Obviously something is still not right so I go to the air handler and check to see if a vacuum is actually being pulled through the entire line set. So here we go, after about 17 feet on the liquid line there is a one way check valve in line, from there it goes to the filter dryer cores then to a solenoid valve (I opened the valve with a solenoid magnet), from there the line continues to evaporator. This section has no vacuum at all. In fact it's still at atmosphere. Okay so for some reason the vacuum will not pull through the txv...but when charged with nitrogen, nitrogen will flow through the entire system. How the hell is this possible that I can pull a vacuum through both high and low side and this section of pipe stays at atmosphere but nitrogen will flow freely through the system? By the way, the reason for the compressor burn out is still not determined yet I am still investigating to rule out everything prior to starting the new compressor up.

[Special-K]

Moved to Tech to Tech

[RLJN]

After a burn out you still have the old filter dryer in the system?

This sounds like a major investment of someone's dollars.
I would probably even change the TXV and any filter driers.

Many TXV's have a reverse flow valve set up that may be adding to the confusion, especially if junk from a burn out is in it.

[Dylan2980]

No, I replaced the filter dryers. Should have said that. We did think of the reverse flow valve set up but then the reverse flow should have the same effect on the nitrogen as well as the vacuum wouldn't it? That's where the confusion is.

[TechmanTerry]

RTU? VRV?

[Dylan2980]

RTU . Daikin RCS unit

[TechmanTerry]

You replaced Factory FD or Field Installed FD's?

[71CHOPS]

Which part of the line was at atmospheric?

The section between the check valve and the LLSV?

Or

The section from the LLSV to the TXV?

Also, is there a relief in the section between the check valve and LLSV? Should have one that is piped back to another section of line open the rest of the system.

[heatingman]

How do you know nitrogen will flow through the entire system?

Where are you pulling vacuum?

Where are you measuring vacuum?


Sent from my iPhone using Tapatalk

[joemach]

Just a thought...

I am not familiar with this system but, is it possible that the valve will open with pressure and close down if it does not see pressure? that is about the only way that I could see this happening.

Or maybe with enough nitrogen pressure it forced the valve open and the vacuum can't do that.

Sorry if I am way off base here but found this thread interesting and jut posted what seems logical to me.