Is this what I think it is?

ratio

This is tied in to the liquid line on a new microchannel rooftop unit. Is it really an expansion tank‽ I knew that microchannel coils didn't hold much juice, but this seems excessive…

(Yes, only the one ¼ line is connected to it.)

EBEBRATT-Ed

I was thinking receiver suction accumulator but with only one connection it's an expansion tank

HVACNUT

Take the strap off man!!
What's it say??
They do that on capacitors too. Put the strap right where the label is.

ratio

I'll look at it the next time I'm out there.

It's inside the condenser section, which means the air over it will be warmer than the air over the condenser, which means it'll be warmer than the condenser, which means that it won't hold much juice when the system's working?

unclejohn

It would be nice to see where the pipe is connected. Is it a heat pump?

ratio

4-5 ton RTU, not a heat pump, single stage compressor (unit was ordered with an economizer). ¼" line goes from the bottom of the tank to the liquid line a foot or so after it leaves the condenser, roughly on the same level as the tank IIRC. No fancy controls, hot gas bypass, or anything like that. Just an expansion tank on the refrigeration circuit.

HVACNUT

Electric expansion valve?
Ambient sensor for 2 speed condenser fan motor?
Condenser fan circuit control opens on liquid line pressure drop?
What make and model RTU?

JUGHNE

Some indoor heat pump coils, in the 80's, had a "liquid reservoir" consisting of about 1" x 12" copper tubing with single port attached to liquid line. This came as part of the coil.

ratio

Brand new Lennox (new install), don't have the model number off hand. Nothing extraordinary about the unit other than the micro channel condenser.

It's obviously a reservoir/expansion tank of some kind, presumably due to the (lack of) internal volume of the condenser coil. So, Lennox either wanted more refrigerant in the system than could safely fit, or certain operating conditions would result in a nosefull of juice that needed a place to hang out in. Or, I suppose, maybe somebody's brother-in-law makes 'em & needed someplace to sell 'em to.

I shore do wonder.

mikeg2015

What model? I have two newer mid range 2 stage Lennox unit. I don’t recall seeing that. Is it a inverter unit?

Lennox and Carrier are notorious for “we know a better way”. While Rheem, Goodman, York, ICP generally have more conventional setups.

mikeg2015

Maybe it’s a muffler of some sort. My 3 ton 16 SEER heat pump is almost as loud as builder grade 13 SEER junk from the 90’s. I added a cheap sound blanket and it’s still loud. Might need a better thicker one. Fan is loud too.

Ironman

Rheem has used those for years to accept refrigerant that the coil won't hold when switching from one mode to the other. They called it a "charge balancer".

ratio

Straight gas heat 1 AC compressor unit. It's certainly an expansion tank, but I can't figure out why (other than the microchannel coil won't hold as much juice as Lennox wants). I'm having a hard time picturing exactly how it's going to effect operation. In warmer weather, it can't possibly be entirely full of liquid when the system is operating because it's in the discharge side of the condenser airflow so it'll be slightly warmer than the subcooling circuit, so more juice is circulating. In cooler weather, I can see the coil gaining enough subcooling for the tank to be full of liquid, so less juice circulating. Maybe it's to do something during the off cycle. IDK.

ChrisJ

> @ratio said:
> Straight gas heat 1 AC compressor unit. It's certainly an expansion tank, but I can't figure out why (other than the microchannel coil won't hold as much juice as Lennox wants). I'm having a hard time picturing exactly how it's going to effect operation. In warmer weather, it can't possibly be entirely full of liquid when the system is operating because it's in the discharge side of the condenser airflow so it'll be slightly warmer than the subcooling circuit, so more juice is circulating. In cooler weather, I can see the coil gaining enough subcooling for the tank to be full of liquid, so less juice circulating. Maybe it's to do something during the off cycle. IDK.

Wouldn't it just act like a receiver?

ratio

Possibly, but a receiver has an in & an out, & temperature could be in play as well. I would imagine that the total cost of a receiver would be cheaper than engineering a different method & giving a new part to the corporate purchasing agent, plus this size & type of unit hasn't traditionally had a receiver in the past.

It's fun to operate the system in my mind & try to find out what's going on. I haven't found out why it exists yet. I'm working backwards from what it does, but I don't have time to just sit and think about it.

HVACNUT

@ratio
First thing tomorrow you get back on that roof and open the manual. There should be an exploded diagram of all replacement parts and their description. Why are you putting us through this anguish?