2 evaporators with single LLSV

[BobFrost]

When we have 2 evaporators in a WI cooler where each evaporator has it's own TXV, why is it a bad idea to put a single liquid line solenoid valve?

[pecmsg]

Who says it’s bad.

You will have to control the frost downstream but that’s easy.

[ammoniadog]

I've never heard that it was bad either. I've put them on top of the box before, and then bull-head teed to both evaps while trying to keep the pipe distances as close to equal as possible. I thought this was the way they were supposed to be done.

I've also installed 2 evaps on one system where both of the evaps came with the solenoids already pre-installed, and also 2 thermostats. I think in that case I left the 2 solenoids in there and rigged up the thermostats so that only one of them worked (one stat controlled both solenoids).

By the way, what's this frost thing you speak of pecmsg? Are you saying the liquid line on the outlet of the solenoid will get cold during pump-down? That's not something I've ever considered before. If that's what you're saying, would you insulate those sections?

[rickl]

It is best to have one pump down solenoid and one cold control. I have freeze up problems otherwise

[TechmanTerry]

I have lots of that set up. I used to do a Beverage Barn kinda place that had 5 evaps on 1 LLSV.

[rider77]

No issues at all doing one LLSV, as long as the one valve is rated to flow enough refrigerant for both coils.
But otherwise it’s very common.

[pecmsg]

I've never heard that it was bad either. I've put them on top of the box before, and then bull-head teed to both evaps while trying to keep the pipe distances as close to equal as possible. I thought this was the way they were supposed to be done.

I've also installed 2 evaps on one system where both of the evaps came with the solenoids already pre-installed, and also 2 thermostats. I think in that case I left the 2 solenoids in there and rigged up the thermostats so that only one of them worked (one stat controlled both solenoids).

By the way, what's this frost thing you speak of pecmsg? Are you saying the liquid line on the outlet of the solenoid will get cold during pump-down? That's not something I've ever considered before. If that's what you're saying, would you insulate those sections?

On rear occasions I’ve seen it happen. Armorflex takes care of it!

[2sac]

I was taught the length of the liquid line should be equal from the solenoid to either metering device.

[Chev5372]

As mentioned should not be a problem as long as the solenoid is sized right for the flow of both TEVs and the liquid line after the solenoid are equal in length , as well as the suction lines.
Try to run the liquid line into the tee on the bullhead , if on the run one valve may not get the same amount of gas. After the TEV that’s on the run starts to pinch off then the valve on the bullhead can get enough gas the pinch back as well. That’s when they start to screw with each other especially if low on charge. Also need to have enough room in the CDU for pump down. Long suction lines and long line after the solenoid may cause high trip during pump down.


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[stanbyyourword]

depends how far apart really, for medium temp I dont see an issure , for low temp you would need to stage the defrosts I think

[icy78]

Last heatcraft class I attended, the equal pipe length thing was scoffed at.
As long as there is not a huge amount of piping friction difference, it really doesnt matter.


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[BobFrost]

Hi guys, thanks for a lot of useful replies.

Who says it’s bad.

I've never heard that it was bad either.

I've been told this on couple of occasions without explanation why it would be bad.
Luckily, there is hvac-talk to clear thing out.


By reading these posts here, I come to conclusion that it's easier to put 2 solenoids (for 2 evaporators) instead of watching out for equal pipe lengths.

[BobFrost]

It is best to have one pump down solenoid and one cold control. I have freeze up problems otherwise

Can you explain it a bit? What causes this freeze up?

[VanMan812]

When each coil has its own LLSV and stat, the first stat could call for cooling and keep the temp low enough to prevent the second stat from closing. With only one coil cooling it will have a very long run time in order to satisfy that stat and will freeze up.

I have units that are setup both ways. One specific unit, a 2 system/
4 evap coil at a C-store isn’t stocked very well and the air doesn’t turn over very well on one end. The coil on the far would freeze up simply because it was so much colder on that side. In that situation I added a second stat so essentially each CU had its own control.

Depending on the type of system and how it’s used both ways can work. More commonly the single stat and LLSV is the way to go.

[ehsx]

Two or more solenoids with single condensing unit can cause oil management issues if suction piping is not self draining/returning from both evaps. Typically I prefer seeing a single llsv.