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Here is a PDF on the issue from Carrier.

Yes, this scroll was certainly pissed off by all the liquid. It scared the crap out of me, I left the system off until the solenoid was installed. Now it works like a charm

Originally Posted by BURL-REF

I agree with a liquid line solenoid. Not pumping the unit down, just closing when the call is satisfied. Install it in the liquid line close to the evaporator. That will keep liquid from migrating on the off cycle.

Originally Posted by Snapperhead

I've seen them at the indoor coil and at the OD unit .... i guess it doesnt really matter

For a long line set application, with the liquid line and evaporator above the condenser, it is best to have a LL solenoid at the outdoor unit to prevent liquid draining back into the condenser and displacing the vapor in the condenser coil.
If the condenser coil and discharge line are full of liquid when the compressor starts, there will be a huge spike in the head pressure for a short time, sometimes even rather violent vibrations. I've seen trip discharge line mounted high pressure switches, and cause cracks in the discharge line due to the vibration.
Scroll compressors sound especially angry starting under those conditions.

A non bleed TXV will take care of things at the evaporator coil end of the lines.

I've seen them at the indoor coil and at the OD unit .... i guess it doesnt really matter

Both should have a yellow wire close by ...

I agree with a liquid line solenoid. Not pumping the unit down, just closing when the call is satisfied. Install it in the liquid line close to the evaporator. That will keep liquid from migrating on the off cycle.

Originally Posted by mark beiser

Since it is a heat pump, make sure you get a bi-flow LL solenoid.

With your lineset length, you won't be able to pump the entire charge down, as there is more refrigerant in the system than can be stored in the condenser.
Use the system to push some out into a recovery cylinder, then pump the system down.

Also, if the system does not have a TXV at the indoor coil, I'd highly recommend installing one, preferably a non bleed type.

A non bleed TXV will help prevent migration to the low side, as well as increase cyclical efficiency in the cooling mode.
LL solenoid at the outdoor unit prevents liquid migration/drain back to the outdoor coil.
Crankcase heater prevents migration to the compressor.
Inverted trap at the indoor coil prevents liquid refrigerant, that condenses in the indoor coil, from running out all at once and slugging the compressor when it starts.

These are the things that will help a system with long lines live a long and happy life.

Holy cow thats alot of work. Just put the OD unit on a pair of stilts

Originally Posted by saintmichael36

The liquid line solenoid would pump down the unit and trap all of the liquid refrigerant before it hits the low side of the system.

Your brain is stuck in Commercial Refrigeration mode .... come back to Residential

In comm refrig , yes LLS pumps the unit down and shuts off with assistance of LPS , but when used in Resi , LLS is generally used as a road block to keep things where they need to stay , and is energized same time as contactor. Its all shut down at once.

Cool. Glad how everything turned out. Isn't it amzing how things work when they are properly installed?

So now the system has a crankcase heater, TXV, inverted trap, and a bi-flow LL solenoid. The solenoid made a big difference, its no longer making that godaweful sound after sitting for a few hours and starting up. Thanks again for the help!

Since it is a heat pump, make sure you get a bi-flow LL solenoid.

With your lineset length, you won't be able to pump the entire charge down, as there is more refrigerant in the system than can be stored in the condenser.
Use the system to push some out into a recovery cylinder, then pump the system down.

Also, if the system does not have a TXV at the indoor coil, I'd highly recommend installing one, preferably a non bleed type.

A non bleed TXV will help prevent migration to the low side, as well as increase cyclical efficiency in the cooling mode.
LL solenoid at the outdoor unit prevents liquid migration/drain back to the outdoor coil.
Crankcase heater prevents migration to the compressor.
Inverted trap at the indoor coil prevents liquid refrigerant, that condenses in the indoor coil, from running out all at once and slugging the compressor when it starts.

These are the things that will help a system with long lines live a long and happy life.

Cool thanks guys (especially Mark Beiser) for the information and explanations. I will throw a LL solenoid in tomorrow. One last quick question, I am going to pump the system down and I'm wondering how many pounds of refrigerant you can jam into a 5 ton compressor. The reason I ask is because I added several pounds to the system to get the charge dialed in, the factory charge is about 15 if my memory serves me. Are these things built to hold 18-20 pounds of refrigerant in a pump down? Also, I'm not 100% sure how much is in the system, I think there was a loss of charge somewhere while it sat in the warehouse for years. I did not hear a refrigerant rush when I cracked the valves and it was way undercharged after adding refrigerant for the lineset length.

Originally Posted by bunny

Bi directional solenoid valve would do the trick.

What is a bi directional solenoid valve?

Never heard of such a thing?

Bi directional solenoid valve would do the trick.

And no need for a p-trap if the evaporator is HIGHER than the condensing unit.

And compressor was "trying to slug liquid"....what on earth does that mean???

Now that makes TOTAL sense. That is exactly what I was thinking, for some reason just could not get it formulated into words.

Thanks Mark, at least I know I was going in the right direction.

Originally Posted by saintmichael36

The liquid line solenoid would pump down the unit and trap all of the liquid refrigerant before it hits the low side of the system.

No, it would be energized and de-energized by calls to Y to the outdoor unit, so it will close when the system cycles off, and open when the system cycles on.
It simply stops the flow of refrigerant when the compressor stops running, no pump down.

Originally Posted by SouthTex

You said this was a heat pump outdoor, would not use a solenoid with a heat pump with out some specical consideration for the heating cycle.

There is no consideration needed, other than making sure the LL solenoid is a bi-flow type.

In a long line set application, with the majority of the liquid line above the condenser, the LL solenoid should be installed within a couple of feet of the outdoor unit.
In addition to reducing refrigerant migration to the low side, it prevents the refrigerant in the liquid line from draining back to, and filling the condenser coil.
When the condenser is filled with liquid there can be some really nasty spikes in discharge pressure, and extreme vibration and compressor noise when a compressor starts up, especially with scroll compressors.

Originally Posted by SouthTex

You said this was a heat pump outdoor, would not use a solenoid with a heat pump with out some specical consideration for the heating cycle. Is there a suction acculator installed between the reversing valve and the compressor? May be an option

I have systems I maintain that are heat pumps with long line sets with a LL solenoid that have run for years with no problem.

I think Mark B. nailed it on what is needed.

You said this was a heat pump outdoor, would not use a solenoid with a heat pump with out some specical consideration for the heating cycle. Is there a suction acculator installed between the reversing valve and the compressor? May be an option

The liquid line solenoid would pump down the unit and trap all of the liquid refrigerant before it hits the low side of the system.


The Day You Think You Know Everything Is The Day You Stop Learning.

The unit has a factory crankcase heater and I have an inverted trap already. How does the liquid line solenoid work? Closes up the LL when the unit is not running I would assume. How would this prevent liquid migrating through the suction line? Thanks

Thanks for the replies fellas. Isnt the suction side supposed to be pulling in vapor not liquid? I have always thought that liquid in the suction line was hard on the compressor, which is why you cant dump a bunch of liquid refrigerant in on the suction side of the system while charging. The lineset does go up about 3" before going horizontally to the ODU location but the compressor is still getting inundated. Could it be because of the long length of the large 1 1/8 lineset holding a few pounds of refrigerant? Maybe there's enough liquid in their to give the compressor a hard start?