Refrigerant migration

Hey guys,

There's something I'm not quite grasping and am hoping someone out there knows the answer.
When a split system using a scroll compressor is installed with the evaporator up in an attic and the condensing unit outside on the ground 20 feet down wouldn't the use of a crank case heater be 100% necessary regardless of lineset length?

I'm asking because it appears most if not all manufacturers say it's not required unless the lineset length is 80' or longer.


On a cooler day where the system has been off and the attic is good and hot from sun loading wouldn't the refrigerant have to migrate to the cooler compressor even with a short lineset?

Why does everyone all of a sudden require a CCH when the lineset hits 80' or longer? Why that magic number? What stops migration in this situation if the lineset is say, 60 feet long?

I think the refrigerant will migrate with either line set length, maybe the thinking behind the crank case heater recommendation (other than cost cutting) is that with a shorter line set there will be less charge to migrate to the compressor and cause problems.

If it were my system I'd fit a crank case heater no matter how long or short the lines.

Refrigerant will migrate because of pressure equalizing when compressor stops. CCH is always good thing to use.
Most manufacturers of small ac units will not use it to cut costs.

Most of the newer a/c units with scroll compressors run a small current through the windings when the unit is off to prevent refrigerant logging in the sump. This does away with a CCH.

Quote:

---

Originally Posted by frank

Most of the newer a/c units with scroll compressors run a small current through the windings when the unit is off to prevent refrigerant logging in the sump. This does away with a CCH.

---

Thank you all for commenting.

It sounds like what I thought is correct, I want some heat on the compressor regardless of what the manufacturers claim.

Frank,
I haven't seen the scenario you describe, at least not yet. All of the wiring diagrams show a contactor that totally disconnects the compressor.

Quote:

---

Originally Posted by MrTube

Frank,
I haven't seen the scenario you describe, at least not yet. All of the wiring diagrams show a contactor that totally disconnects the compressor.

---

As I say, it is the newer models, i.e. inverter driven, that have this
Does your unit have an accumulator?

Quote:

---

Originally Posted by frank

As I say, it is the newer models, i.e. inverter driven, that have this
Does your unit have an accumulator?

---

Ah I see.
No, no accumulator.