TXV or something else?

[sdumper]

I have a first stage with a TXV on a cascade and the TXV is acting really strange. The pressure is the same as it was when I tuned it and the adjustment bolt was not moved but the TXV is no longer cooling down at the initial screw adjustment. I initially assumed that orifice must have gotten clogged so I replaced the orifice and recharged and still no change. I'm not using a sight glass (tried to save money and never had much use for them before ... lesson learned ) so I thought maybe somehow the receiver on.off adjustment NUT must have somehow twisted itself into a closed position (I know unlikely) anyway that's not the issue. Whats weird is that if I turn the TXV to almost full closed it frosts up (just wont hold load) but when its moved to the midpoint or full open nothing.... Low side Full open -30psi and full closed -10psi. High side 220psi either way...

Static is what I always use for r404 175psi.

I am about to order a new TXV and stick a sight glass on ...also change the filter drier but have any of you had this happen before? I am really short on money and buying a TXV, sight glass and filter drier replacement is close to 150.00...

[Gray Mole]

Well a -30psi with a charge is almost always a blockage.

Sounds like you have fullopen/full closed backwards considering the low pressure.

I've run into bad TXV's, but it just doesn't taste like it. System sounds like a pumpdown at the -30psi level.

Sightglass is so much easier, hardly have to think about tuning. You can check if it's got the charge with subcooling measurement though. Get the temps of it running, pressure vs pipe temp before the TXV at the most likely point of liquid head (usually the filter location if it's set up like a reciever) and that will tell you if it's got enough gas to provide liquid head.

Without liquid head the TXV just won't work right.

Could also explain the behaviour, having to close the TXV to create a liquid head and start the cooling process.

Static pressure is a good start, sure, but you can have the pressure and still not have enough gas to condense enough to get liquid at the TXV.

Get pics, and temp readings at the usual points of testing and label them if you can.

Also, if it's cold where you're testing, lower or shut down the airflow of the condensor to 'spike' the pressure. Sometimes if it's cool enough, the gas won't condense the way you think it should. PT behaviour is just like that.

More info on temps and might be able to help more. Wouldn't order up that stuff until you can get a real diagnostic.

Gray

[sdumper]

The TXV set at factory default was frosting and pulling down as normal. Then with no changes at all it suddenly stopped working.
I'm leaning towards blockage but with no cap the blockage is limited to TXV or orifice and the orifice has been replaced.

Just ordered the replacement TXV and will pick up a filter drier and sit glass at united. Ill keep you guys updated.

Ill check the orientation again to make sure im not mixing up the open closed because it would be a cheap fix

[closeracing]

The TXV set at factory default was frosting and pulling down as normal. Then with no changes at all it suddenly stopped working.
I'm leaning towards blockage but with no cap the blockage is limited to TXV or orifice and the orifice has been replaced.

Just ordered the replacement TXV and will pick up a filter drier and sit glass at united. Ill keep you guys updated.

Ill check the orientation again to make sure im not mixing up the open closed because it would be a cheap fix

Wow what an ordeal. I hope it is something simple like that.
I appreciate you going the extra mile to get this resolved

[sdumper]

Wow what an ordeal. I hope it is something simple like that.
I appreciate you going the extra mile to get this resolved

Derek its the least I could do.
Worst case scenario I will rebuild the first stage with a new compressor, receiver, sight glass, TXV and filter drier.
It wont take me that long to do so but I want to try and isolate the issue before I take drastic steps like that.

Regardless, Im picking up a sight glass tomorrow and will add it so I can visual see the refrigerant flowing.

[Gray Mole]

Sightglass is definitely the easiest way to see if you have liquid, but if you're unsure...

Run the system, try to ensure you've got a minimum of 30c condensing temp, measure the temp 5 or 6 inches before the TXV on the supply, and compare pressure vs temp.

If you have a discharge pressure of 220psi, and lower than 35c where you want the liquid, should be cool.

4-5 degrees below HP is ideal.

That's where it get's a little iffy though.

If you can increase the condensing temp to 40c but don't see a HP increase, and still have a relatively high vac/unsuitably low LP then you're either pumping down due to a blockage, or have too little refrigerant.

On full pumpdown, you'll see a HP equal to the amount of refrigerant in the system vs HP volume.

Hope adding the glass makes this one easier for you, but there's a couple details to keep in mind.

Using a rotary, with no load even at max charge, -10psig is pretty much with what you'd expect, and 220psig high not really far off either (hypothetical).

Just talking to myself really, temp readings, pressure readings system details, etc would all be needed to know anything for sure. I just enjoy the diagnostic end of it. When I do it at work, it's just work. Here, it get's fun

Gray

[ultralo1]

So if i am reading this right, no matter which way you adjust the TXV you do not get any significant frost formation and you suction stays in the vacuum range? Sounds like a restriction.

Some TXVs have a filter screen in the "input" side. Also I have noticed with cap tubes and POE that has become hot, a wax like substance will form in the cap tube. It may be worth pulling the TX and checking it.

[sdumper]

Just received my replacement txv today and will replace tomorrow.

[closeracing]

Just received my replacement txv today and will replace tomorrow.

WOOHOO!!! Hope that solves it

[sdumper]

WOOHOO!!! Hope that solves it

Im sure it will. Its either the TXV, the orifice (which was changed), a clog in the reciever (highly unlikely) or the filter Drier. Not too many things can go wrong with the first stage. Should be able to wrap it up and send out Monday.

[Slayer68]

Sounds like a restricted capilary to me. Several times I've had misdiagnosed TXV failures and it's always been a restriction. If you opened up that TXV and nothing happened odds are that downstream of the expansion valve is restricted. Could also be overcharged with oil or you could have air in the system because it didn't get evacuated properly. The smaller the system the more critical the little things become.

[sdumper]

Sounds like a restricted capilary to me. Several times I've had misdiagnosed TXV failures and it's always been a restriction. If you opened up that TXV and nothing happened odds are that downstream of the expansion valve is restricted. Could also be overcharged with oil or you could have air in the system because it didn't get evacuated properly. The smaller the system the more critical the little things become.

• Not overcharge with oil
• No air in the system vacuumed and recharged 3 times while trouble shooting
• This is first stage of a cascade with NO cap tube

[sdumper]

Removed the TXV and the powerhead line to the bulb was sheered.
No clue how that happened but will attach the new TXV, vacuum over night and then recharge.

Still might not be the issue but I have parts to build a complete stage 1 replacement if it came down to that.

[sdumper]

Replaced the TXV and works like a charm....
This is where flare nuts are worth there weight in gold.

[closeracing]

Replaced the TXV and works like a charm....
This is where flare nuts are worth there weight in gold.

Awesome Scott great work!
I'll be getting the cart ready this weekend to mount the PID's and switches. How much longer did you make the wires? I'll need an idea so I know where to cut the holes.

[sdumper]

Awesome Scott great work!
I'll be getting the cart ready this weekend to mount the PID's and switches. How much longer did you make the wires? I'll need an idea so I know where to cut the holes.

I added a new 4 foot pid wire to the hx and 3 feet of per switch wires. Not sure about the suction line because it may be shorter ill have to measure.

[closeracing]

I added a new 4 foot pid wire to the hx

is this for the 1st stage

Not sure about the suction line because it may be shorter ill have to measure.

And this the 2nd?

[closeracing]

I guess I'll find out when it arrives.