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Havnt checked. Will surely take a look monday.

Is there a pressure drop between the evap and the compressor?

I know TXV's are not pressure regulators, But I have seen coils running proper superheat but overloading the suction line and raising the SST. had to increase superheats in order to reduce the load on the suction line to achive desired SST.

It's rare, but I've seen it

Originally Posted by icemeister

The superheat could still stand to be bit lower to around 4-6°F. You'd be amazed at how much difference it can make. But be sure you're measuring the suction pressure at the coil and not at the compressor when you figure the SH because that couple of pounds of pressure drop in the suction line will throw you way off in a hurry at these temperatures.

Your subcooling usually won't get much higher than what you've got simply because it's got a receiver in the system. There's no adjusting that with charge...or anything else. And yes, by definition at 3°F SC you'll have a clear glass.

Get it out of your head about altering the suction pressure by messing around with the expansion valve. It's not a pressure regulator...it's a superheat regulator.

As for the nozzle question, we've already made a fix of sorts by upsizing the TXV capacity. This did one of two things. Either the nozzle was actually OK sizewise and the TXV was undersized...or the other way 'round. So at this point, unless you find you can't get the SH down to where you need it, I wouldn't be concerned about the nozzle sizing. The superheat is a major factor in telling you whether the coil is performing or not.

The one thing which stands out here is the relatively high TD on the evaporator. You say the box is at 0°F and the coil is at -20°F SST, which gives a 20°F TD. At design conditions it should be a 10°F...but what are the design conditions for this job?

By the numbers we have, the coil has a specific capacity of 9400 Btuh at a 10°F TD and the condensing unit has a capacity of about 9400 Btuh at -20°F SST and 90°F ambient, so I'm assuming the system was selected for a -10°F box temperature...correct?

I think a lower superheat will help lower the TD and subsequently raise the suction pressure & lower the box temperature...but another 10°F lower may be a push. Of course there may be other factors in play here.

Yes im measuring pressure and temp at the evap. Ill drop the SH a few degrees. I know it is achievable. After the box got down to temp I adjusted the valve and went a little to far so can get it to 4 no problem.

Good deal on the SC then.

Yea I know the tev controls SH. With the smaller cartridge pressure was more of where I wanted it at around 8 or 10 psi but as already discussed, I couldnt get SH below 25 at the evap. I did have a colder box though..

Glad I wont have to unbraze the valve and pull the nozzle.

The box is in ambient conditions. That was accounted for when they sized it. They set it up for 115 degree ambient and a -15 degree box.

Ill swing by monday and get the sh to 4 and see how it goes. Just seems like its struggling to maintain 0 and sub 0 temps and is running 24/7, except for three defrost cycles.

Would just like to point out the amount of knowledge in this thread. I don't post as often as I should, but read this forum multiple times a week and for any tech that wants to be better this is the place to be. AR...happy you fixed the problem!

Originally Posted by crackertech

Just a thought I once had coil we ordered fore R-22 but it was shipped with a 404 orifice in it drove us crazy.

That's what I was thinking too. But should see some movement with the adjustment. Wouldn't waste alot of time here. Pull it, verify orifice, and replace valve. Assuming you are confident the charge is correct.

Originally Posted by ar_hvac_man

Me again Margaret....

Had a free minute to go check how the freezer is doing. Everything checks out good except my pressure and coil temp. SH 8deg at the bulb. Pressure 15 psi....-20 degree coil. Box hovers at 0 and wont get colder obviously because my suction is too high. My SC is also low at 3 deg but I have a clear sight glass?

Good SH but I want lower suction so the box will pull down. To get lower suction pressure Id have to squeeze down the TXV which will raise my SH and my evap wont be flooded.

The distributor nozzle subject keeps scratching at my brain. Can someone explain how going to a bigger nozzle would help?

The superheat could still stand to be bit lower to around 4-6°F. You'd be amazed at how much difference it can make. But be sure you're measuring the suction pressure at the coil and not at the compressor when you figure the SH because that couple of pounds of pressure drop in the suction line will throw you way off in a hurry at these temperatures.

Your subcooling usually won't get much higher than what you've got simply because it's got a receiver in the system. There's no adjusting that with charge...or anything else. And yes, by definition at 3°F SC you'll have a clear glass.

Get it out of your head about altering the suction pressure by messing around with the expansion valve. It's not a pressure regulator...it's a superheat regulator.

As for the nozzle question, we've already made a fix of sorts by upsizing the TXV capacity. This did one of two things. Either the nozzle was actually OK sizewise and the TXV was undersized...or the other way 'round. So at this point, unless you find you can't get the SH down to where you need it, I wouldn't be concerned about the nozzle sizing. The superheat is a major factor in telling you whether the coil is performing or not.

The one thing which stands out here is the relatively high TD on the evaporator. You say the box is at 0°F and the coil is at -20°F SST, which gives a 20°F TD. At design conditions it should be a 10°F...but what are the design conditions for this job?

By the numbers we have, the coil has a specific capacity of 9400 Btuh at a 10°F TD and the condensing unit has a capacity of about 9400 Btuh at -20°F SST and 90°F ambient, so I'm assuming the system was selected for a -10°F box temperature...correct?

I think a lower superheat will help lower the TD and subsequently raise the suction pressure & lower the box temperature...but another 10°F lower may be a push. Of course there may be other factors in play here.

Granted, it could have been the wrong one in the bag i guess. Ive only installed around 12 complete new cooler or freezer systems. This is the first Ive had any problem with. Ill know in the future to verify correct nozzle sizing. How would a bigger nozzle help is what im asking.

I installed the low temp 404A nozzle that came with the evap

Originally Posted by ar_hvac_man

Me again Margaret....

Had a free minute to go check how the freezer is doing. Everything checks out good except my pressure and coil temp. SH 8deg at the bulb. Pressure 15 psi....-20 degree coil. Box hovers at 0 and wont get colder obviously because my suction is too high. My SC is also low at 3 deg but I have a clear sight glass?

Good SH but I want lower suction so the box will pull down. To get lower suction pressure Id have to squeeze down the TXV which will raise my SH and my evap wont be flooded.

The distributor nozzle subject keeps scratching at my brain. Can someone explain how going to a bigger nozzle would help?

First do you know if the right nozzle was installed???

Me again Margaret....

Had a free minute to go check how the freezer is doing. Everything checks out good except my pressure and coil temp. SH 8deg at the bulb. Pressure 15 psi....-20 degree coil. Box hovers at 0 and wont get colder obviously because my suction is too high. My SC is also low at 3 deg but I have a clear sight glass?

Good SH but I want lower suction so the box will pull down. To get lower suction pressure Id have to squeeze down the TXV which will raise my SH and my evap wont be flooded.

The distributor nozzle subject keeps scratching at my brain. Can someone explain how going to a bigger nozzle would help?

Is the box sealed? Are there any air gaps on the door?

Originally Posted by ar_hvac_man

Changed powerhead, no change. Put in the number 4 and shes rockin and rollin

Thanks guys!

Great news!!!

You mean I got it right???

I've had this happen enough times to make me wonder about the distributor nozzle sizing for Heatcraft (and possibly others). The reasoning is if the nozzle is undersized, there will be a lower available pressure drop across the expansion valve and therefore prevent it's operation at full flow capacity. By upsizing the expansion valve (or its orifice size in this case) you may well correct the flow problem, but not the actual cause.

So...It would have been helpful to know the distributor nozzle size.

In the meantime, I tend to lean toward simply going up one size on the TXV from what's called for. Unless you have a system with floating head pressure or unloading, I doubt you'll ever have a TXV control problem from its being oversized.

Good... Glad that is put to bed.

I really wish Icemeister knew what he was doing... I mean, really? Come on....

Changed powerhead, no change. Put in the number 4 and shes rockin and rollin

Thanks guys!

Originally Posted by ar_hvac_man

LOL! Thats wrong TB.

I know, I know. Sometimes, the morning DJ comes back out....

Originally Posted by timebuilder

Let me see if I following this.

We have refrigerant that is no longer a virgin, some bad head, and an orifice that is too small.

I have the answer.


The unit is 12.

LOL! Thats wrong TB.

Originally Posted by timebuilder

Let me see if I following this.

We have refrigerant that is no longer a virgin, some bad head, and an orifice that is too small.

I have the answer.


The unit is 12.

Witty comment with held.

Originally Posted by Dad

I think I know what the issue is.

Your incoming voltage is running backwards and the refrigerant isn't a virgin anymore.

What ya think? .... go fix that thang so we know what's going on.

Let me see if I following this.

We have refrigerant that is no longer a virgin, some bad head, and an orifice that is too small.

I have the answer.


The unit is 12.