Mini split nitrogen test???

[MushCreek]

I'm doing a high pressure nitrogen test on a new mini split I'm installing, and discovered something weird. The high pressure fitting was leaking, so I drained the system to re-do it. I let the pressure off of the port, which is on the low pressure line, but the high pressure line remained pressurized. I loosened the flare fitting, and it let the pressure off, but it was under a lot of pressure. The only thing I can figure is that there's a check valve in the indoor unit. Fine. BUT- How can you evacuate the system then? After I do a successful nitrogen test, the high pressure line is still going to be full of nitrogen. If there's a check valve, the vacuum won't be able to pull it down. The low pressure line will be evacuated, but not the high pressure line. How does that work?

 

[PoorUB]

There shouldn't be anything preventing nitrogen to flow through the system.

Did you braze or solder any fitting? Perhaps you plugged up a line with solder.

 

[MushCreek]

The nitrogen flows through, but apparently only one way. How can I remove the hose from the service port and still have pressure in the high pressure line? I removed the valve core, so it's wide open. There are no soldered fittings- everything is a flare fitting.

 

[Terry D]

That should be straight through. The valves are out in the condensor. You had to do something wrong. Was the vavle core out or in. If it was left in, and you removed the hose from the valve, what was depressing the core in

 

[Jim greengo]

I'm doing a high pressure nitrogen test on a new mini split I'm installing, and discovered something weird. The high pressure fitting was leaking, so I drained the system to re-do it. I let the pressure off of the port, which is on the low pressure line, but the high pressure line remained pressurized. I loosened the flare fitting, and it let the pressure off, but it was under a lot of pressure. The only thing I can figure is that there's a check valve in the indoor unit. Fine. BUT- How can you evacuate the system then? After I do a successful nitrogen test, the high pressure line is still going to be full of nitrogen. If there's a check valve, the vacuum won't be able to pull it down. The low pressure line will be evacuated, but not the high pressure line. How does that work?

Is there a txv in the system?

 

[Terry D]

Is there a txv in the system?

Isn't the TXV's out in the condenser on a minisplit

 

[Jim greengo]

Not sure,most of my experiance is with package units and regular split systems.
Just throwing ideas out there.

 

[Terry D]

OP, while you have the high side line disconnected from the flare on the service valve, hook your nitrogen tank back up on the low side Schrader and verify you have a flow of nitrogen from there, through the evaporator and out the line outside. Then take out the core on the low side and hold the hose on the high side line, you should have flow both ways. There are no one way valves in the inside unit. Your service valves are still closed correct? Is refrigerant is still contained in the condenser? Is this the same unit you posted about a couple of weeks ago where you pulled oil from your vacuum pump possibly into the system?

 

[MushCreek]

OK; mystery solved. The adapter I used to fit the hose to the port also has a Schrader valve! I just never looked, to be honest. The pressure of the nitrogen was enough to pressurize the line, but the Schrader kept it from draining down after I disconnected the hose. D'oh!
Yes, it's the same system I was working on before. No oil got into the system. It didn't even get into the hose between the manifold and the system, so I'm good there. I had ordered more tools to do the job right, and it took a while to get them. Then, it rained all of last week, and I didn't feel like working on it in the rain. The good news is that it held 400 psi for 24 hours, so at least I know that there are no leaks. I'm pressure testing it again, because the torque setting in the manual destroys the flare on the small 1/4" line. It just mashes it into foil. I don't know if it's my cheap torque wrench, the **** refrigerant lines, or if the information in the manual is simply wrong. In looking it up online, the torque called for is only 8-10 ft/lbs. I'm using a flare crow foot, set at 90 degrees to keep the torque accurate.

 

[Terry D]

OK; mystery solved. The adapter I used to fit the hose to the port also has a Schrader valve! I just never looked, to be honest. The pressure of the nitrogen was enough to pressurize the line, but the Schrader kept it from draining down after I disconnected the hose. D'oh!
Yes, it's the same system I was working on before. No oil got into the system. It didn't even get into the hose between the manifold and the system, so I'm good there. I had ordered more tools to do the job right, and it took a while to get them. Then, it rained all of last week, and I didn't feel like working on it in the rain. The good news is that it held 400 psi for 24 hours, so at least I know that there are no leaks. I'm pressure testing it again, because the torque setting in the manual destroys the flare on the small 1/4" line. It just mashes it into foil. I don't know if it's my cheap torque wrench, the **** refrigerant lines, or if the information in the manual is simply wrong. In looking it up online, the torque called for is only 8-10 ft/lbs. I'm using a flare crow foot, set at 90 degrees to keep the torque accurate.

Good that you got it figured out. I had the same problem on my 1/4" line. Had the same set up. Regular torque wrench with a crows foot at 90 degrees. Ended up just tightening with wrenches